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MDEV-26145: Incorrect metadata is sent on running query with union in PS mode

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Test cases like the following one produce different result sets if it's run
with and without th option --ps-protocol.

CREATE TABLE t1(a INT);
--enable_metadata
(SELECT MAX(a) FROM t1) UNION (SELECT MAX(a) FROM t1);
--disable_metadata
DROP TABLE t1;

Result sets differ in metadata for the query
  (SELECT MAX(a) FROM t1) UNION (SELECT MAX(a) FROM t1);

The reason for different content of query metadata is that for queries
with union the items being created on JOIN preparing phase is placed into
item_list from SELECT_LEX_UNIT whereas for queries without union item_list
from SELECT_LEX is used instead.
This commit is contained in:
Dmitry Shulga
2021-07-19 19:25:11 +07:00
parent c47e4aab62
commit bab989ab38
4 changed files with 81 additions and 1 deletions
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7
sql/sql_prepare.cc
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@ -1674,7 +1674,12 @@ static int mysql_test_select(Prepared_statement *stmt,
if (!lex->describe && !thd->lex->analyze_stmt && !stmt->is_sql_prepare())
{
/* Make copy of item list, as change_columns may change it */
List<Item> fields(lex->select_lex.item_list);
SELECT_LEX_UNIT* master_unit= unit->first_select()->master_unit();
bool is_union_op=
master_unit->is_union() || master_unit->fake_select_lex;
List<Item> fields(is_union_op ? unit->item_list :
lex->select_lex.item_list);
/* Change columns if a procedure like analyse() */
if (unit->last_procedure && unit->last_procedure->change_columns(thd, fields))