Bug#23345: Wrongly allowed INTO in a non-last select of a UNION.

INTO clause can be specified only for the last select of a UNION and it
receives the result of the whole query. But it was wrongly allowed in
non-last selects of a UNION which leads to a confusing query result.

Now INTO allowed only in the last select of a UNION.

mysql-test/r/union.result

@@ -1381,4 +1381,12 @@ a
 SELECT a FROM (SELECT a FROM t1 UNION SELECT a FROM t1 ORDER BY c) AS test;
 ERROR 42S22: Unknown column 'c' in 'order clause'
 DROP TABLE t1;
+(select 1 into @var) union (select 1);
+ERROR HY000: Incorrect usage of UNION and INTO
+(select 1) union (select 1 into @var);
+select @var;
+@var
+1
+(select 2) union (select 1 into @var);
+ERROR 42000: Result consisted of more than one row
 End of 5.0 tests

mysql-test/t/union.test

@@ -868,4 +868,13 @@ SELECT a FROM (SELECT a FROM t1 UNION SELECT a FROM t1 ORDER BY c) AS test;
 
 DROP TABLE t1;
 
+#
+# Bug#23345: Wrongly allowed INTO in a non-last select of a UNION.
+#
+--error 1221
+(select 1 into @var) union (select 1);
+(select 1) union (select 1 into @var);
+select @var;
+--error 1172
+(select 2) union (select 1 into @var);
 --echo End of 5.0 tests

sql/sql_yacc.yy

@@ -9307,7 +9307,7 @@ union_list:
 	UNION_SYM union_option
 	{
 	  LEX *lex=Lex;
-	  if (lex->exchange)
+	  if (lex->result)
 	  {
 	    /* Only the last SELECT can have  INTO...... */
 	    my_error(ER_WRONG_USAGE, MYF(0), "UNION", "INTO");