Rucha Deodhar 6a7a44aba0 MDEV-5092: Implement UPDATE with result set (UPDATE ... RETURNING) ...

The patch introduces the OLD_VALUE() expression to reference the value
of a column before it was updated. The parser is extended to support
RETURNING and OLD_VALUE(), and RETURNING expressions are stored in a
separate returning_list in SELECT_LEX with independent wildcard tracking.
RETURNING is rejected for multi-table UPDATE.

During setup of RETURNING fields, THD::is_setting_returning is used
when resolving fields, particularly for updates through views.
When resolving view fields, Item_direct_view_ref may point to the
view's item_list, losing the information about whether the value
should be old or new. The original item in returning_list still
contains the correct is_old_value_reference flag, which is copied
back to the resolved item.

OLD_VALUE() is implemented by extending Item_field with a new
Item_old_field class. Item_field::set_field() initializes
Field::ptr_old to the corresponding location in record[1],
which stores the old row during UPDATE execution.

When sending result rows, Item_old_field::send() temporarily switches
the field pointer from record[0] (current row) to ptr_old so
OLD_VALUE() returns the value before the update.

The UPDATE execution path is modified to send a result set when
RETURNING is present instead of an OK packet.

2026-04-30 09:41:26 -04:00

67 KiB

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