diff options
Diffstat (limited to 'lib/sqlalchemy/sql/expression.py')
| -rw-r--r-- | lib/sqlalchemy/sql/expression.py | 10 |
1 files changed, 9 insertions, 1 deletions
diff --git a/lib/sqlalchemy/sql/expression.py b/lib/sqlalchemy/sql/expression.py index 2f0ac90af..acfb3d7c4 100644 --- a/lib/sqlalchemy/sql/expression.py +++ b/lib/sqlalchemy/sql/expression.py @@ -1498,7 +1498,15 @@ class _CompareMixin(ColumnOperators): args.append(o) if len(args) == 0: - # Special case handling for empty IN's, behave like comparison against zero row selectable + # Special case handling for empty IN's, behave like comparison + # against zero row selectable. We use != to build the + # contradiction as it handles NULL values appropriately, i.e. + # "not (x IN ())" should not return NULL values for x. + util.warn("The IN-predicate on \"%s\" was invoked with an empty sequence. " + "This results in a contradiction, which nonetheless can be " + "expensive to evaluate. Consider alternative strategies for " + "improved performance." % self) + return self != self return self.__compare(op, ClauseList(*args).self_group(against=op), negate=negate_op) |