- The INSERT...FROM SELECT construct now implies ``inline=True``

on :class:`.Insert`.  This helps to fix a bug where an
INSERT...FROM SELECT construct would inadvertently be compiled
as "implicit returning" on supporting backends, which would
cause breakage in the case of an INSERT that inserts zero rows
(as implicit returning expects a row), as well as arbitrary
return data in the case of an INSERT that inserts multiple
rows (e.g. only the first row of many).
A similar change is also applied to an INSERT..VALUES
with multiple parameter sets; implicit RETURNING will no longer emit
for this statement either.  As both of these constructs deal
with varible numbers of rows, the
:attr:`.ResultProxy.inserted_primary_key` accessor does not
apply.   Previously, there was a documentation note that one
may prefer ``inline=True`` with INSERT..FROM SELECT as some databases
don't support returning and therefore can't do "implicit" returning,
but there's no reason an INSERT...FROM SELECT needs implicit returning
in any case.   Regular explicit :meth:`.Insert.returning` should
be used to return variable numbers of result rows if inserted
data is needed.
fixes #3169

1 files changed, 3 insertions, 1 deletions

diff --git a/lib/sqlalchemy/sql/compiler.py b/lib/sqlalchemy/sql/compiler.py
index e45510aa4..fac4980b0 100644
--- a/lib/sqlalchemy/sql/compiler.py
+++ b/lib/sqlalchemy/sql/compiler.py
@@ -1981,11 +1981,13 @@ class SQLCompiler(Compiled):
 
         need_pks = self.isinsert and \
             not self.inline and \
-            not stmt._returning
+            not stmt._returning and \
+            not stmt._has_multi_parameters
 
         implicit_returning = need_pks and \
             self.dialect.implicit_returning and \
             stmt.table.implicit_returning
+
         if self.isinsert:
             implicit_return_defaults = (implicit_returning and
                                         stmt._return_defaults)