/venv/lib/python2.7/site-packages/sqlalchemy/sql/compiler.py

# sql/compiler.py
# Copyright (C) 2005-2016 the SQLAlchemy authors and contributors
# <see AUTHORS file>
#
# This module is part of SQLAlchemy and is released under
# the MIT License: http://www.opensource.org/licenses/mit-license.php

"""Base SQL and DDL compiler implementations.

Classes provided include:

:class:`.compiler.SQLCompiler` - renders SQL
strings

:class:`.compiler.DDLCompiler` - renders DDL
(data definition language) strings

:class:`.compiler.GenericTypeCompiler` - renders
type specification strings.

To generate user-defined SQL strings, see
:doc:`/ext/compiler`.

"""

import contextlib
import re
from . import schema, sqltypes, operators, functions, visitors, \
    elements, selectable, crud
from .. import util, exc
import itertools

RESERVED_WORDS = set([
    'all', 'analyse', 'analyze', 'and', 'any', 'array',
    'as', 'asc', 'asymmetric', 'authorization', 'between',
    'binary', 'both', 'case', 'cast', 'check', 'collate',
    'column', 'constraint', 'create', 'cross', 'current_date',
    'current_role', 'current_time', 'current_timestamp',
    'current_user', 'default', 'deferrable', 'desc',
    'distinct', 'do', 'else', 'end', 'except', 'false',
    'for', 'foreign', 'freeze', 'from', 'full', 'grant',
    'group', 'having', 'ilike', 'in', 'initially', 'inner',
    'intersect', 'into', 'is', 'isnull', 'join', 'leading',
    'left', 'like', 'limit', 'localtime', 'localtimestamp',
    'natural', 'new', 'not', 'notnull', 'null', 'off', 'offset',
    'old', 'on', 'only', 'or', 'order', 'outer', 'overlaps',
    'placing', 'primary', 'references', 'right', 'select',
    'session_user', 'set', 'similar', 'some', 'symmetric', 'table',
    'then', 'to', 'trailing', 'true', 'union', 'unique', 'user',
    'using', 'verbose', 'when', 'where'])

LEGAL_CHARACTERS = re.compile(r'^[A-Z0-9_$]+$', re.I)
ILLEGAL_INITIAL_CHARACTERS = set([str(x) for x in range(0, 10)]).union(['$'])

BIND_PARAMS = re.compile(r'(?<![:\w\$\x5c]):([\w\$]+)(?![:\w\$])', re.UNICODE)
BIND_PARAMS_ESC = re.compile(r'\x5c(:[\w\$]*)(?![:\w\$])', re.UNICODE)

BIND_TEMPLATES = {
    'pyformat': "%%(%(name)s)s",
    'qmark': "?",
    'format': "%%s",
    'numeric': ":[_POSITION]",
    'named': ":%(name)s"
}


OPERATORS = {
    # binary
    operators.and_: ' AND ',
    operators.or_: ' OR ',
    operators.add: ' + ',
    operators.mul: ' * ',
    operators.sub: ' - ',
    operators.div: ' / ',
    operators.mod: ' % ',
    operators.truediv: ' / ',
    operators.neg: '-',
    operators.lt: ' < ',
    operators.le: ' <= ',
    operators.ne: ' != ',
    operators.gt: ' > ',
    operators.ge: ' >= ',
    operators.eq: ' = ',
    operators.concat_op: ' || ',
    operators.match_op: ' MATCH ',
    operators.notmatch_op: ' NOT MATCH ',
    operators.in_op: ' IN ',
    operators.notin_op: ' NOT IN ',
    operators.comma_op: ', ',
    operators.from_: ' FROM ',
    operators.as_: ' AS ',
    operators.is_: ' IS ',
    operators.isnot: ' IS NOT ',
    operators.collate: ' COLLATE ',

    # unary
    operators.exists: 'EXISTS ',
    operators.distinct_op: 'DISTINCT ',
    operators.inv: 'NOT ',

    # modifiers
    operators.desc_op: ' DESC',
    operators.asc_op: ' ASC',
    operators.nullsfirst_op: ' NULLS FIRST',
    operators.nullslast_op: ' NULLS LAST',

}

FUNCTIONS = {
    functions.coalesce: 'coalesce%(expr)s',
    functions.current_date: 'CURRENT_DATE',
    functions.current_time: 'CURRENT_TIME',
    functions.current_timestamp: 'CURRENT_TIMESTAMP',
    functions.current_user: 'CURRENT_USER',
    functions.localtime: 'LOCALTIME',
    functions.localtimestamp: 'LOCALTIMESTAMP',
    functions.random: 'random%(expr)s',
    functions.sysdate: 'sysdate',
    functions.session_user: 'SESSION_USER',
    functions.user: 'USER'
}

EXTRACT_MAP = {
    'month': 'month',
    'day': 'day',
    'year': 'year',
    'second': 'second',
    'hour': 'hour',
    'doy': 'doy',
    'minute': 'minute',
    'quarter': 'quarter',
    'dow': 'dow',
    'week': 'week',
    'epoch': 'epoch',
    'milliseconds': 'milliseconds',
    'microseconds': 'microseconds',
    'timezone_hour': 'timezone_hour',
    'timezone_minute': 'timezone_minute'
}

COMPOUND_KEYWORDS = {
    selectable.CompoundSelect.UNION: 'UNION',
    selectable.CompoundSelect.UNION_ALL: 'UNION ALL',
    selectable.CompoundSelect.EXCEPT: 'EXCEPT',
    selectable.CompoundSelect.EXCEPT_ALL: 'EXCEPT ALL',
    selectable.CompoundSelect.INTERSECT: 'INTERSECT',
    selectable.CompoundSelect.INTERSECT_ALL: 'INTERSECT ALL'
}


class Compiled(object):

    """Represent a compiled SQL or DDL expression.

    The ``__str__`` method of the ``Compiled`` object should produce
    the actual text of the statement.  ``Compiled`` objects are
    specific to their underlying database dialect, and also may
    or may not be specific to the columns referenced within a
    particular set of bind parameters.  In no case should the
    ``Compiled`` object be dependent on the actual values of those
    bind parameters, even though it may reference those values as
    defaults.
    """

    _cached_metadata = None

    def __init__(self, dialect, statement, bind=None,
                 compile_kwargs=util.immutabledict()):
        """Construct a new ``Compiled`` object.

        :param dialect: ``Dialect`` to compile against.

        :param statement: ``ClauseElement`` to be compiled.

        :param bind: Optional Engine or Connection to compile this
          statement against.

        :param compile_kwargs: additional kwargs that will be
         passed to the initial call to :meth:`.Compiled.process`.

         .. versionadded:: 0.8

        """

        self.dialect = dialect
        self.bind = bind
        if statement is not None:
            self.statement = statement
            self.can_execute = statement.supports_execution
            self.string = self.process(self.statement, **compile_kwargs)

    @util.deprecated("0.7", ":class:`.Compiled` objects now compile "
                     "within the constructor.")
    def compile(self):
        """Produce the internal string representation of this element.
        """
        pass

    def _execute_on_connection(self, connection, multiparams, params):
        return connection._execute_compiled(self, multiparams, params)

    @property
    def sql_compiler(self):
        """Return a Compiled that is capable of processing SQL expressions.

        If this compiler is one, it would likely just return 'self'.

        """

        raise NotImplementedError()

    def process(self, obj, **kwargs):
        return obj._compiler_dispatch(self, **kwargs)

    def __str__(self):
        """Return the string text of the generated SQL or DDL."""

        return self.string or ''

    def construct_params(self, params=None):
        """Return the bind params for this compiled object.

        :param params: a dict of string/object pairs whose values will
                       override bind values compiled in to the
                       statement.
        """

        raise NotImplementedError()

    @property
    def params(self):
        """Return the bind params for this compiled object."""
        return self.construct_params()

    def execute(self, *multiparams, **params):
        """Execute this compiled object."""

        e = self.bind
        if e is None:
            raise exc.UnboundExecutionError(
                "This Compiled object is not bound to any Engine "
                "or Connection.")
        return e._execute_compiled(self, multiparams, params)

    def scalar(self, *multiparams, **params):
        """Execute this compiled object and return the result's
        scalar value."""

        return self.execute(*multiparams, **params).scalar()


class TypeCompiler(util.with_metaclass(util.EnsureKWArgType, object)):
    """Produces DDL specification for TypeEngine objects."""

    ensure_kwarg = 'visit_\w+'

    def __init__(self, dialect):
        self.dialect = dialect

    def process(self, type_, **kw):
        return type_._compiler_dispatch(self, **kw)


class _CompileLabel(visitors.Visitable):

    """lightweight label object which acts as an expression.Label."""

    __visit_name__ = 'label'
    __slots__ = 'element', 'name'

    def __init__(self, col, name, alt_names=()):
        self.element = col
        self.name = name
        self._alt_names = (col,) + alt_names

    @property
    def proxy_set(self):
        return self.element.proxy_set

    @property
    def type(self):
        return self.element.type



class SQLCompiler(Compiled):

    """Default implementation of Compiled.

    Compiles ClauseElements into SQL strings.   Uses a similar visit
    paradigm as visitors.ClauseVisitor but implements its own traversal.

    """

    extract_map = EXTRACT_MAP

    compound_keywords = COMPOUND_KEYWORDS

    isdelete = isinsert = isupdate = False
    """class-level defaults which can be set at the instance
    level to define if this Compiled instance represents
    INSERT/UPDATE/DELETE
    """

    isplaintext = False

    returning = None
    """holds the "returning" collection of columns if
    the statement is CRUD and defines returning columns
    either implicitly or explicitly
    """

    returning_precedes_values = False
    """set to True classwide to generate RETURNING
    clauses before the VALUES or WHERE clause (i.e. MSSQL)
    """

    render_table_with_column_in_update_from = False
    """set to True classwide to indicate the SET clause
    in a multi-table UPDATE statement should qualify
    columns with the table name (i.e. MySQL only)
    """

    ansi_bind_rules = False
    """SQL 92 doesn't allow bind parameters to be used
    in the columns clause of a SELECT, nor does it allow
    ambiguous expressions like "? = ?".  A compiler
    subclass can set this flag to False if the target
    driver/DB enforces this
    """

    def __init__(self, dialect, statement, column_keys=None,
                 inline=False, **kwargs):
        """Construct a new ``DefaultCompiler`` object.

        dialect
          Dialect to be used

        statement
          ClauseElement to be compiled

        column_keys
          a list of column names to be compiled into an INSERT or UPDATE
          statement.

        """
        self.column_keys = column_keys

        # compile INSERT/UPDATE defaults/sequences inlined (no pre-
        # execute)
        self.inline = inline or getattr(statement, 'inline', False)

        # a dictionary of bind parameter keys to BindParameter
        # instances.
        self.binds = {}

        # a dictionary of BindParameter instances to "compiled" names
        # that are actually present in the generated SQL
        self.bind_names = util.column_dict()

        # stack which keeps track of nested SELECT statements
        self.stack = []

        # relates label names in the final SQL to a tuple of local
        # column/label name, ColumnElement object (if any) and
        # TypeEngine. ResultProxy uses this for type processing and
        # column targeting
        self._result_columns = []

        # if False, means we can't be sure the list of entries
        # in _result_columns is actually the rendered order.   This
        # gets flipped when we use TextAsFrom, for example.
        self._ordered_columns = True

        # true if the paramstyle is positional
        self.positional = dialect.positional
        if self.positional:
            self.positiontup = []
        self.bindtemplate = BIND_TEMPLATES[dialect.paramstyle]

        self.ctes = None

        # an IdentifierPreparer that formats the quoting of identifiers
        self.preparer = dialect.identifier_preparer
        self.label_length = dialect.label_length \
            or dialect.max_identifier_length

        # a map which tracks "anonymous" identifiers that are created on
        # the fly here
        self.anon_map = util.PopulateDict(self._process_anon)

        # a map which tracks "truncated" names based on
        # dialect.label_length or dialect.max_identifier_length
        self.truncated_names = {}
        Compiled.__init__(self, dialect, statement, **kwargs)

        if self.positional and dialect.paramstyle == 'numeric':
            self._apply_numbered_params()

    @util.memoized_instancemethod
    def _init_cte_state(self):
        """Initialize collections related to CTEs only if
        a CTE is located, to save on the overhead of
        these collections otherwise.

        """
        # collect CTEs to tack on top of a SELECT
        self.ctes = util.OrderedDict()
        self.ctes_by_name = {}
        self.ctes_recursive = False
        if self.positional:
            self.cte_positional = {}

    @contextlib.contextmanager
    def _nested_result(self):
        """special API to support the use case of 'nested result sets'"""
        result_columns, ordered_columns = (
            self._result_columns, self._ordered_columns)
        self._result_columns, self._ordered_columns = [], False

        try:
            if self.stack:
                entry = self.stack[-1]
                entry['need_result_map_for_nested'] = True
            else:
                entry = None
            yield self._result_columns, self._ordered_columns
        finally:
            if entry:
                entry.pop('need_result_map_for_nested')
            self._result_columns, self._ordered_columns = (
                result_columns, ordered_columns)

    def _apply_numbered_params(self):
        poscount = itertools.count(1)
        self.string = re.sub(
            r'\[_POSITION\]',
            lambda m: str(util.next(poscount)),
            self.string)

    @util.memoized_property
    def _bind_processors(self):
        return dict(
            (key, value) for key, value in
            ((self.bind_names[bindparam],
              bindparam.type._cached_bind_processor(self.dialect))
             for bindparam in self.bind_names)
            if value is not None
        )

    def is_subquery(self):
        return len(self.stack) > 1

    @property
    def sql_compiler(self):
        return self

    def construct_params(self, params=None, _group_number=None, _check=True):
        """return a dictionary of bind parameter keys and values"""

        if params:
            pd = {}
            for bindparam in self.bind_names:
                name = self.bind_names[bindparam]
                if bindparam.key in params:
                    pd[name] = params[bindparam.key]
                elif name in params:
                    pd[name] = params[name]

                elif _check and bindparam.required:
                    if _group_number:
                        raise exc.InvalidRequestError(
                            "A value is required for bind parameter %r, "
                            "in parameter group %d" %
                            (bindparam.key, _group_number))
                    else:
                        raise exc.InvalidRequestError(
                            "A value is required for bind parameter %r"
                            % bindparam.key)

                elif bindparam.callable:
                    pd[name] = bindparam.effective_value
                else:
                    pd[name] = bindparam.value
            return pd
        else:
            pd = {}
            for bindparam in self.bind_names:
                if _check and bindparam.required:
                    if _group_number:
                        raise exc.InvalidRequestError(
                            "A value is required for bind parameter %r, "
                            "in parameter group %d" %
                            (bindparam.key, _group_number))
                    else:
                        raise exc.InvalidRequestError(
                            "A value is required for bind parameter %r"
                            % bindparam.key)

                if bindparam.callable:
                    pd[self.bind_names[bindparam]] = bindparam.effective_value
                else:
                    pd[self.bind_names[bindparam]] = bindparam.value
            return pd

    @property
    def params(self):
        """Return the bind param dictionary embedded into this
        compiled object, for those values that are present."""
        return self.construct_params(_check=False)

    @util.dependencies("sqlalchemy.engine.result")
    def _create_result_map(self, result):
        """utility method used for unit tests only."""
        return result.ResultMetaData._create_result_map(self._result_columns)

    def default_from(self):
        """Called when a SELECT statement has no froms, and no FROM clause is
        to be appended.

        Gives Oracle a chance to tack on a ``FROM DUAL`` to the string output.

        """
        return ""

    def visit_grouping(self, grouping, asfrom=False, **kwargs):
        return "(" + grouping.element._compiler_dispatch(self, **kwargs) + ")"

    def visit_label_reference(
            self, element, within_columns_clause=False, **kwargs):
        if self.stack and self.dialect.supports_simple_order_by_label:
            selectable = self.stack[-1]['selectable']

            with_cols, only_froms = selectable._label_resolve_dict
            if within_columns_clause:
                resolve_dict = only_froms
            else:
                resolve_dict = with_cols

            # this can be None in the case that a _label_reference()
            # were subject to a replacement operation, in which case
            # the replacement of the Label element may have changed
            # to something else like a ColumnClause expression.
            order_by_elem = element.element._order_by_label_element

            if order_by_elem is not None and order_by_elem.name in \
                    resolve_dict:

                kwargs['render_label_as_label'] = \
                    element.element._order_by_label_element

        return self.process(
            element.element, within_columns_clause=within_columns_clause,
            **kwargs)

    def visit_textual_label_reference(
            self, element, within_columns_clause=False, **kwargs):
        if not self.stack:
            # compiling the element outside of the context of a SELECT
            return self.process(
                element._text_clause
            )

        selectable = self.stack[-1]['selectable']
        with_cols, only_froms = selectable._label_resolve_dict
        try:
            if within_columns_clause:
                col = only_froms[element.element]
            else:
                col = with_cols[element.element]
        except KeyError:
            # treat it like text()
            util.warn_limited(
                "Can't resolve label reference %r; converting to text()",
                util.ellipses_string(element.element))
            return self.process(
                element._text_clause
            )
        else:
            kwargs['render_label_as_label'] = col
            return self.process(
                col, within_columns_clause=within_columns_clause, **kwargs)

    def visit_label(self, label,
                    add_to_result_map=None,
                    within_label_clause=False,
                    within_columns_clause=False,
                    render_label_as_label=None,
                    **kw):
        # only render labels within the columns clause
        # or ORDER BY clause of a select.  dialect-specific compilers
        # can modify this behavior.
        render_label_with_as = (within_columns_clause and not
                                within_label_clause)
        render_label_only = render_label_as_label is label

        if render_label_only or render_label_with_as:
            if isinstance(label.name, elements._truncated_label):
                labelname = self._truncated_identifier("colident", label.name)
            else:
                labelname = label.name

        if render_label_with_as:
            if add_to_result_map is not None:
                add_to_result_map(
                    labelname,
                    label.name,
                    (label, labelname, ) + label._alt_names,
                    label.type
                )

            return label.element._compiler_dispatch(
                self, within_columns_clause=True,
                within_label_clause=True, **kw) + \
                OPERATORS[operators.as_] + \
                self.preparer.format_label(label, labelname)
        elif render_label_only:
            return self.preparer.format_label(label, labelname)
        else:
            return label.element._compiler_dispatch(
                self, within_columns_clause=False, **kw)

    def visit_column(self, column, add_to_result_map=None,
                     include_table=True, **kwargs):
        name = orig_name = column.name
        if name is None:
            raise exc.CompileError("Cannot compile Column object until "
                                   "its 'name' is assigned.")

        is_literal = column.is_literal
        if not is_literal and isinstance(name, elements._truncated_label):
            name = self._truncated_identifier("colident", name)

        if add_to_result_map is not None:
            add_to_result_map(
                name,
                orig_name,
                (column, name, column.key),
                column.type
            )

        if is_literal:
            name = self.escape_literal_column(name)
        else:
            name = self.preparer.quote(name)

        table = column.table
        if table is None or not include_table or not table.named_with_column:
            return name
        else:
            if table.schema:
                schema_prefix = self.preparer.quote_schema(table.schema) + '.'
            else:
                schema_prefix = ''
            tablename = table.name
            if isinstance(tablename, elements._truncated_label):
                tablename = self._truncated_identifier("alias", tablename)

            return schema_prefix + \
                self.preparer.quote(tablename) + \
                "." + name

    def escape_literal_column(self, text):
        """provide escaping for the literal_column() construct."""

        # TODO: some dialects might need different behavior here
        return text.replace('%', '%%')

    def visit_fromclause(self, fromclause, **kwargs):
        return fromclause.name

    def visit_index(self, index, **kwargs):
        return index.name

    def visit_typeclause(self, typeclause, **kw):
        kw['type_expression'] = typeclause
        return self.dialect.type_compiler.process(typeclause.type, **kw)

    def post_process_text(self, text):
        return text

    def visit_textclause(self, textclause, **kw):
        def do_bindparam(m):
            name = m.group(1)
            if name in textclause._bindparams:
                return self.process(textclause._bindparams[name], **kw)
            else:
                return self.bindparam_string(name, **kw)

        if not self.stack:
            self.isplaintext = True

        # un-escape any \:params
        return BIND_PARAMS_ESC.sub(
            lambda m: m.group(1),
            BIND_PARAMS.sub(
                do_bindparam,
                self.post_process_text(textclause.text))
        )

    def visit_text_as_from(self, taf,
                           compound_index=None,
                           asfrom=False,
                           parens=True, **kw):

        toplevel = not self.stack
        entry = self._default_stack_entry if toplevel else self.stack[-1]

        populate_result_map = toplevel or \
            (
                compound_index == 0 and entry.get(
                    'need_result_map_for_compound', False)
            ) or entry.get('need_result_map_for_nested', False)

        if populate_result_map:
            self._ordered_columns = False
            for c in taf.column_args:
                self.process(c, within_columns_clause=True,
                             add_to_result_map=self._add_to_result_map)

        text = self.process(taf.element, **kw)
        if asfrom and parens:
            text = "(%s)" % text
        return text

    def visit_null(self, expr, **kw):
        return 'NULL'

    def visit_true(self, expr, **kw):
        if self.dialect.supports_native_boolean:
            return 'true'
        else:
            return "1"

    def visit_false(self, expr, **kw):
        if self.dialect.supports_native_boolean:
            return 'false'
        else:
            return "0"

    def visit_clauselist(self, clauselist, **kw):
        sep = clauselist.operator
        if sep is None:
            sep = " "
        else:
            sep = OPERATORS[clauselist.operator]
        return sep.join(
            s for s in
            (
                c._compiler_dispatch(self, **kw)
                for c in clauselist.clauses)
            if s)

    def visit_case(self, clause, **kwargs):
        x = "CASE "
        if clause.value is not None:
            x += clause.value._compiler_dispatch(self, **kwargs) + " "
        for cond, result in clause.whens:
            x += "WHEN " + cond._compiler_dispatch(
                self, **kwargs
            ) + " THEN " + result._compiler_dispatch(
                self, **kwargs) + " "
        if clause.else_ is not None:
            x += "ELSE " + clause.else_._compiler_dispatch(
                self, **kwargs
            ) + " "
        x += "END"
        return x

    def visit_cast(self, cast, **kwargs):
        return "CAST(%s AS %s)" % \
            (cast.clause._compiler_dispatch(self, **kwargs),
             cast.typeclause._compiler_dispatch(self, **kwargs))

    def visit_over(self, over, **kwargs):
        return "%s OVER (%s)" % (
            over.func._compiler_dispatch(self, **kwargs),
            ' '.join(
                '%s BY %s' % (word, clause._compiler_dispatch(self, **kwargs))
                for word, clause in (
                    ('PARTITION', over.partition_by),
                    ('ORDER', over.order_by)
                )
                if clause is not None and len(clause)
            )
        )

    def visit_funcfilter(self, funcfilter, **kwargs):
        return "%s FILTER (WHERE %s)" % (
            funcfilter.func._compiler_dispatch(self, **kwargs),
            funcfilter.criterion._compiler_dispatch(self, **kwargs)
        )

    def visit_extract(self, extract, **kwargs):
        field = self.extract_map.get(extract.field, extract.field)
        return "EXTRACT(%s FROM %s)" % (
            field, extract.expr._compiler_dispatch(self, **kwargs))

    def visit_function(self, func, add_to_result_map=None, **kwargs):
        if add_to_result_map is not None:
            add_to_result_map(
                func.name, func.name, (), func.type
            )

        disp = getattr(self, "visit_%s_func" % func.name.lower(), None)
        if disp:
            return disp(func, **kwargs)
        else:
            name = FUNCTIONS.get(func.__class__, func.name + "%(expr)s")
            return ".".join(list(func.packagenames) + [name]) % \
                {'expr': self.function_argspec(func, **kwargs)}

    def visit_next_value_func(self, next_value, **kw):
        return self.visit_sequence(next_value.sequence)

    def visit_sequence(self, sequence):
        raise NotImplementedError(
            "Dialect '%s' does not support sequence increments." %
            self.dialect.name
        )

    def function_argspec(self, func, **kwargs):
        return func.clause_expr._compiler_dispatch(self, **kwargs)

    def visit_compound_select(self, cs, asfrom=False,
                              parens=True, compound_index=0, **kwargs):
        toplevel = not self.stack
        entry = self._default_stack_entry if toplevel else self.stack[-1]
        need_result_map = toplevel or \
            (compound_index == 0
                and entry.get('need_result_map_for_compound', False))

        self.stack.append(
            {
                'correlate_froms': entry['correlate_froms'],
                'asfrom_froms': entry['asfrom_froms'],
                'selectable': cs,
                'need_result_map_for_compound': need_result_map
            })

        keyword = self.compound_keywords.get(cs.keyword)

        text = (" " + keyword + " ").join(
            (c._compiler_dispatch(self,
                                  asfrom=asfrom, parens=False,
                                  compound_index=i, **kwargs)
             for i, c in enumerate(cs.selects))
        )

        group_by = cs._group_by_clause._compiler_dispatch(
            self, asfrom=asfrom, **kwargs)
        if group_by:
            text += " GROUP BY " + group_by

        text += self.order_by_clause(cs, **kwargs)
        text += (cs._limit_clause is not None
                 or cs._offset_clause is not None) and \
            self.limit_clause(cs, **kwargs) or ""

        if self.ctes and toplevel:
            text = self._render_cte_clause() + text

        self.stack.pop(-1)
        if asfrom and parens:
            return "(" + text + ")"
        else:
            return text

    def visit_unary(self, unary, **kw):
        if unary.operator:
            if unary.modifier:
                raise exc.CompileError(
                    "Unary expression does not support operator "
                    "and modifier simultaneously")
            disp = getattr(self, "visit_%s_unary_operator" %
                           unary.operator.__name__, None)
            if disp:
                return disp(unary, unary.operator, **kw)
            else:
                return self._generate_generic_unary_operator(
                    unary, OPERATORS[unary.operator], **kw)
        elif unary.modifier:
            disp = getattr(self, "visit_%s_unary_modifier" %
                           unary.modifier.__name__, None)
            if disp:
                return disp(unary, unary.modifier, **kw)
            else:
                return self._generate_generic_unary_modifier(
                    unary, OPERATORS[unary.modifier], **kw)
        else:
            raise exc.CompileError(
                "Unary expression has no operator or modifier")

    def visit_istrue_unary_operator(self, element, operator, **kw):
        if self.dialect.supports_native_boolean:
            return self.process(element.element, **kw)
        else:
            return "%s = 1" % self.process(element.element, **kw)

    def visit_isfalse_unary_operator(self, element, operator, **kw):
        if self.dialect.supports_native_boolean:
            return "NOT %s" % self.process(element.element, **kw)
        else:
            return "%s = 0" % self.process(element.element, **kw)

    def visit_notmatch_op_binary(self, binary, operator, **kw):
        return "NOT %s" % self.visit_binary(
            binary, override_operator=operators.match_op)

    def visit_binary(self, binary, override_operator=None, **kw):
        # don't allow "? = ?" to render
        if self.ansi_bind_rules and \
                isinstance(binary.left, elements.BindParameter) and \
                isinstance(binary.right, elements.BindParameter):
            kw['literal_binds'] = True

        operator_ = override_operator or binary.operator
        disp = getattr(self, "visit_%s_binary" % operator_.__name__, None)
        if disp:
            return disp(binary, operator_, **kw)
        else:
            try:
                opstring = OPERATORS[operator_]
            except KeyError:
                raise exc.UnsupportedCompilationError(self, operator_)
            else:
                return self._generate_generic_binary(binary, opstring, **kw)

    def visit_custom_op_binary(self, element, operator, **kw):
        return self._generate_generic_binary(
            element, " " + operator.opstring + " ", **kw)

    def visit_custom_op_unary_operator(self, element, operator, **kw):
        return self._generate_generic_unary_operator(
            element, operator.opstring + " ", **kw)

    def visit_custom_op_unary_modifier(self, element, operator, **kw):
        return self._generate_generic_unary_modifier(
            element, " " + operator.opstring, **kw)

    def _generate_generic_binary(self, binary, opstring, **kw):
        return binary.left._compiler_dispatch(self, **kw) + \
            opstring + \
            binary.right._compiler_dispatch(self, **kw)

    def _generate_generic_unary_operator(self, unary, opstring, **kw):
        return opstring + unary.element._compiler_dispatch(self, **kw)

    def _generate_generic_unary_modifier(self, unary, opstring, **kw):
        return unary.element._compiler_dispatch(self, **kw) + opstring

    @util.memoized_property
    def _like_percent_literal(self):
        return elements.literal_column("'%'", type_=sqltypes.STRINGTYPE)

    def visit_contains_op_binary(self, binary, operator, **kw):
        binary = binary._clone()
        percent = self._like_percent_literal
        binary.right = percent.__add__(binary.right).__add__(percent)
        return self.visit_like_op_binary(binary, operator, **kw)

    def visit_notcontains_op_binary(self, binary, operator, **kw):
        binary = binary._clone()
        percent = self._like_percent_literal
        binary.right = percent.__add__(binary.right).__add__(percent)
        return self.visit_notlike_op_binary(binary, operator, **kw)

    def visit_startswith_op_binary(self, binary, operator, **kw):
        binary = binary._clone()
        percent = self._like_percent_literal
        binary.right = percent.__radd__(
            binary.right
        )
        return self.visit_like_op_binary(binary, operator, **kw)

    def visit_notstartswith_op_binary(self, binary, operator, **kw):
        binary = binary._clone()
        percent = self._like_percent_literal
        binary.right = percent.__radd__(
            binary.right
        )
        return self.visit_notlike_op_binary(binary, operator, **kw)

    def visit_endswith_op_binary(self, binary, operator, **kw):
        binary = binary._clone()
        percent = self._like_percent_literal
        binary.right = percent.__add__(binary.right)
        return self.visit_like_op_binary(binary, operator, **kw)

    def visit_notendswith_op_binary(self, binary, operator, **kw):
        binary = binary._clone()
        percent = self._like_percent_literal
        binary.right = percent.__add__(binary.right)
        return self.visit_notlike_op_binary(binary, operator, **kw)

    def visit_like_op_binary(self, binary, operator, **kw):
        escape = binary.modifiers.get("escape", None)

        # TODO: use ternary here, not "and"/ "or"
        return '%s LIKE %s' % (
            binary.left._compiler_dispatch(self, **kw),
            binary.right._compiler_dispatch(self, **kw)) \
            + (
                ' ESCAPE ' +
                self.render_literal_value(escape, sqltypes.STRINGTYPE)
                if escape else ''
            )

    def visit_notlike_op_binary(self, binary, operator, **kw):
        escape = binary.modifiers.get("escape", None)
        return '%s NOT LIKE %s' % (
            binary.left._compiler_dispatch(self, **kw),
            binary.right._compiler_dispatch(self, **kw)) \
            + (
                ' ESCAPE ' +
                self.render_literal_value(escape, sqltypes.STRINGTYPE)
                if escape else ''
            )

    def visit_ilike_op_binary(self, binary, operator, **kw):
        escape = binary.modifiers.get("escape", None)
        return 'lower(%s) LIKE lower(%s)' % (
            binary.left._compiler_dispatch(self, **kw),
            binary.right._compiler_dispatch(self, **kw)) \
            + (
                ' ESCAPE ' +
                self.render_literal_value(escape, sqltypes.STRINGTYPE)
                if escape else ''
            )

    def visit_notilike_op_binary(self, binary, operator, **kw):
        escape = binary.modifiers.get("escape", None)
        return 'lower(%s) NOT LIKE lower(%s)' % (
            binary.left._compiler_dispatch(self, **kw),
            binary.right._compiler_dispatch(self, **kw)) \
            + (
                ' ESCAPE ' +
                self.render_literal_value(escape, sqltypes.STRINGTYPE)
                if escape else ''
            )

    def visit_between_op_binary(self, binary, operator, **kw):
        symmetric = binary.modifiers.get("symmetric", False)
        return self._generate_generic_binary(
            binary, " BETWEEN SYMMETRIC "
            if symmetric else " BETWEEN ", **kw)

    def visit_notbetween_op_binary(self, binary, operator, **kw):
        symmetric = binary.modifiers.get("symmetric", False)
        return self._generate_generic_binary(
            binary, " NOT BETWEEN SYMMETRIC "
            if symmetric else " NOT BETWEEN ", **kw)

    def visit_bindparam(self, bindparam, within_columns_clause=False,
                        literal_binds=False,
                        skip_bind_expression=False,
                        **kwargs):
        if not skip_bind_expression and bindparam.type._has_bind_expression:
            bind_expression = bindparam.type.bind_expression(bindparam)
            return self.process(bind_expression,
                                skip_bind_expression=True)

        if literal_binds or \
            (within_columns_clause and
                self.ansi_bind_rules):
            if bindparam.value is None and bindparam.callable is None:
                raise exc.CompileError("Bind parameter '%s' without a "
                                       "renderable value not allowed here."
                                       % bindparam.key)
            return self.render_literal_bindparam(
                bindparam, within_columns_clause=True, **kwargs)

        name = self._truncate_bindparam(bindparam)

        if name in self.binds:
            existing = self.binds[name]
            if existing is not bindparam:
                if (existing.unique or bindparam.unique) and \
                    not existing.proxy_set.intersection(
                        bindparam.proxy_set):
                    raise exc.CompileError(
                        "Bind parameter '%s' conflicts with "
                        "unique bind parameter of the same name" %
                        bindparam.key
                    )
                elif existing._is_crud or bindparam._is_crud:
                    raise exc.CompileError(
                        "bindparam() name '%s' is reserved "
                        "for automatic usage in the VALUES or SET "
                        "clause of this "
                        "insert/update statement.   Please use a "
                        "name other than column name when using bindparam() "
                        "with insert() or update() (for example, 'b_%s')." %
                        (bindparam.key, bindparam.key)
                    )

        self.binds[bindparam.key] = self.binds[name] = bindparam

        return self.bindparam_string(name, **kwargs)

    def render_literal_bindparam(self, bindparam, **kw):
        value = bindparam.effective_value
        return self.render_literal_value(value, bindparam.type)

    def render_literal_value(self, value, type_):
        """Render the value of a bind parameter as a quoted literal.

        This is used for statement sections that do not accept bind parameters
        on the target driver/database.

        This should be implemented by subclasses using the quoting services
        of the DBAPI.

        """

        processor = type_._cached_literal_processor(self.dialect)
        if processor:
            return processor(value)
        else:
            raise NotImplementedError(
                "Don't know how to literal-quote value %r" % value)

    def _truncate_bindparam(self, bindparam):
        if bindparam in self.bind_names:
            return self.bind_names[bindparam]

        bind_name = bindparam.key
        if isinstance(bind_name, elements._truncated_label):
            bind_name = self._truncated_identifier("bindparam", bind_name)

        # add to bind_names for translation
        self.bind_names[bindparam] = bind_name

        return bind_name

    def _truncated_identifier(self, ident_class, name):
        if (ident_class, name) in self.truncated_names:
            return self.truncated_names[(ident_class, name)]

        anonname = name.apply_map(self.anon_map)

        if len(anonname) > self.label_length - 6:
            counter = self.truncated_names.get(ident_class, 1)
            truncname = anonname[0:max(self.label_length - 6, 0)] + \
                "_" + hex(counter)[2:]
            self.truncated_names[ident_class] = counter + 1
        else:
            truncname = anonname
        self.truncated_names[(ident_class, name)] = truncname
        return truncname

    def _anonymize(self, name):
        return name % self.anon_map

    def _process_anon(self, key):
        (ident, derived) = key.split(' ', 1)
        anonymous_counter = self.anon_map.get(derived, 1)
        self.anon_map[derived] = anonymous_counter + 1
        return derived + "_" + str(anonymous_counter)

    def bindparam_string(self, name, positional_names=None, **kw):
        if self.positional:
            if positional_names is not None:
                positional_names.append(name)
            else:
                self.positiontup.append(name)
        return self.bindtemplate % {'name': name}

    def visit_cte(self, cte, asfrom=False, ashint=False,
                  fromhints=None,
                  **kwargs):
        self._init_cte_state()

        if isinstance(cte.name, elements._truncated_label):
            cte_name = self._truncated_identifier("alias", cte.name)
        else:
            cte_name = cte.name

        if cte_name in self.ctes_by_name:
            existing_cte = self.ctes_by_name[cte_name]
            # we've generated a same-named CTE that we are enclosed in,
            # or this is the same CTE.  just return the name.
            if cte in existing_cte._restates or cte is existing_cte:
                return self.preparer.format_alias(cte, cte_name)
            elif existing_cte in cte._restates:
                # we've generated a same-named CTE that is
                # enclosed in us - we take precedence, so
                # discard the text for the "inner".
                del self.ctes[existing_cte]
            else:
                raise exc.CompileError(
                    "Multiple, unrelated CTEs found with "
                    "the same name: %r" %
                    cte_name)

        self.ctes_by_name[cte_name] = cte

        if cte._cte_alias is not None:
            orig_cte = cte._cte_alias
            if orig_cte not in self.ctes:
                self.visit_cte(orig_cte, **kwargs)
            cte_alias_name = cte._cte_alias.name
            if isinstance(cte_alias_name, elements._truncated_label):
                cte_alias_name = self._truncated_identifier(
                    "alias", cte_alias_name)
        else:
            orig_cte = cte
            cte_alias_name = None
        if not cte_alias_name and cte not in self.ctes:
            if cte.recursive:
                self.ctes_recursive = True
            text = self.preparer.format_alias(cte, cte_name)
            if cte.recursive:
                if isinstance(cte.original, selectable.Select):
                    col_source = cte.original
                elif isinstance(cte.original, selectable.CompoundSelect):
                    col_source = cte.original.selects[0]
                else:
                    assert False
                recur_cols = [c for c in
                              util.unique_list(col_source.inner_columns)
                              if c is not None]

                text += "(%s)" % (", ".join(
                    self.preparer.format_column(ident)
                    for ident in recur_cols))

            if self.positional:
                kwargs['positional_names'] = self.cte_positional[cte] = []

            text += " AS \n" + \
                cte.original._compiler_dispatch(
                    self, asfrom=True, **kwargs
                )

            if cte._suffixes:
                text += " " + self._generate_prefixes(
                    cte, cte._suffixes, **kwargs)

            self.ctes[cte] = text

        if asfrom:
            if cte_alias_name:
                text = self.preparer.format_alias(cte, cte_alias_name)
                text += self.get_render_as_alias_suffix(cte_name)
            else:
                return self.preparer.format_alias(cte, cte_name)
            return text

    def visit_alias(self, alias, asfrom=False, ashint=False,
                    iscrud=False,
                    fromhints=None, **kwargs):
        if asfrom or ashint:
            if isinstance(alias.name, elements._truncated_label):
                alias_name = self._truncated_identifier("alias", alias.name)
            else:
                alias_name = alias.name

        if ashint:
            return self.preparer.format_alias(alias, alias_name)
        elif asfrom:
            ret = alias.original._compiler_dispatch(self,
                                                    asfrom=True, **kwargs) + \
                self.get_render_as_alias_suffix(
                    self.preparer.format_alias(alias, alias_name))

            if fromhints and alias in fromhints:
                ret = self.format_from_hint_text(ret, alias,
                                                 fromhints[alias], iscrud)

            return ret
        else:
            return alias.original._compiler_dispatch(self, **kwargs)

    def get_render_as_alias_suffix(self, alias_name_text):
        return " AS " + alias_name_text

    def _add_to_result_map(self, keyname, name, objects, type_):
        self._result_columns.append((keyname, name, objects, type_))

    def _label_select_column(self, select, column,
                             populate_result_map,
                             asfrom, column_clause_args,
                             name=None,
                             within_columns_clause=True):
        """produce labeled columns present in a select()."""

        if column.type._has_column_expression and \
                populate_result_map:
            col_expr = column.type.column_expression(column)
            add_to_result_map = lambda keyname, name, objects, type_: \
                self._add_to_result_map(
                    keyname, name,
                    objects + (column,), type_)
        else:
            col_expr = column
            if populate_result_map:
                add_to_result_map = self._add_to_result_map
            else:
                add_to_result_map = None

        if not within_columns_clause:
            result_expr = col_expr
        elif isinstance(column, elements.Label):
            if col_expr is not column:
                result_expr = _CompileLabel(
                    col_expr,
                    column.name,
                    alt_names=(column.element,)
                )
            else:
                result_expr = col_expr

        elif select is not None and name:
            result_expr = _CompileLabel(
                col_expr,
                name,
                alt_names=(column._key_label,)
            )

        elif \
            asfrom and \
            isinstance(column, elements.ColumnClause) and \
            not column.is_literal and \
            column.table is not None and \
                not isinstance(column.table, selectable.Select):
            result_expr = _CompileLabel(col_expr,
                                        elements._as_truncated(column.name),
                                        alt_names=(column.key,))
        elif (
            not isinstance(column, elements.TextClause) and
            (
                not isinstance(column, elements.UnaryExpression) or
                column.wraps_column_expression
            ) and
            (
                not hasattr(column, 'name') or
                isinstance(column, functions.Function)
            )
        ):
            result_expr = _CompileLabel(col_expr, column.anon_label)
        elif col_expr is not column:
            # TODO: are we sure "column" has a .name and .key here ?
            # assert isinstance(column, elements.ColumnClause)
            result_expr = _CompileLabel(col_expr,
                                        elements._as_truncated(column.name),
                                        alt_names=(column.key,))
        else:
            result_expr = col_expr

        column_clause_args.update(
            within_columns_clause=within_columns_clause,
            add_to_result_map=add_to_result_map
        )
        return result_expr._compiler_dispatch(
            self,
            **column_clause_args
        )

    def format_from_hint_text(self, sqltext, table, hint, iscrud):
        hinttext = self.get_from_hint_text(table, hint)
        if hinttext:
            sqltext += " " + hinttext
        return sqltext

    def get_select_hint_text(self, byfroms):
        return None

    def get_from_hint_text(self, table, text):
        return None

    def get_crud_hint_text(self, table, text):
        return None

    def get_statement_hint_text(self, hint_texts):
        return " ".join(hint_texts)

    def _transform_select_for_nested_joins(self, select):
        """Rewrite any "a JOIN (b JOIN c)" expression as
        "a JOIN (select * from b JOIN c) AS anon", to support
        databases that can't parse a parenthesized join correctly
        (i.e. sqlite the main one).

        """
        cloned = {}
        column_translate = [{}]

        def visit(element, **kw):
            if element