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-rw-r--r--lib/sqlalchemy/sql/compiler.py24
1 files changed, 24 insertions, 0 deletions
diff --git a/lib/sqlalchemy/sql/compiler.py b/lib/sqlalchemy/sql/compiler.py
index bfa22c206..a1d5a879d 100644
--- a/lib/sqlalchemy/sql/compiler.py
+++ b/lib/sqlalchemy/sql/compiler.py
@@ -1003,6 +1003,30 @@ class SQLCompiler(Compiled):
return "NOT %s" % self.visit_binary(
binary, override_operator=operators.match_op)
+ def _emit_empty_in_warning(self):
+ util.warn(
+ 'The IN-predicate was invoked with an '
+ 'empty sequence. This results in a '
+ 'contradiction, which nonetheless can be '
+ 'expensive to evaluate. Consider alternative '
+ 'strategies for improved performance.')
+
+ def visit_empty_in_op_binary(self, binary, operator, **kw):
+ if self.dialect._use_static_in:
+ return "1 != 1"
+ else:
+ if self.dialect._warn_on_empty_in:
+ self._emit_empty_in_warning()
+ return self.process(binary.left != binary.left)
+
+ def visit_empty_notin_op_binary(self, binary, operator, **kw):
+ if self.dialect._use_static_in:
+ return "1 = 1"
+ else:
+ if self.dialect._warn_on_empty_in:
+ self._emit_empty_in_warning()
+ return self.process(binary.left == binary.left)
+
def visit_binary(self, binary, override_operator=None,
eager_grouping=False, **kw):