CREATE TABLE t1 (

  a INT,

  b INT,

  PRIMARY KEY (a),

  KEY ab(a, b)

);

INSERT INTO t1 VALUES (1,1),(2,2),(3,3),(4,4);

INSERT INTO t1 SELECT a + 4, b + 4 FROM t1;

--disable_query_log

--let $q = `show status like 'Created_tmp_tables';`

eval set @tmp_tables_before = 

  CAST(REPLACE('$q', 'Created_tmp_tables', '') AS UNSIGNED);

--enable_query_log

SELECT a FROM t1 IGNORE INDEX FOR GROUP BY (a, ab) GROUP BY a;

--disable_query_log

--let $q = `show status like 'Created_tmp_tables';`

eval set @tmp_tables_after = 

  CAST(REPLACE('$q', 'Created_tmp_tables', '') AS UNSIGNED);

--enable_query_log

SELECT @tmp_tables_after;

SELECT @tmp_tables_before ;

SELECT @tmp_tables_after = @tmp_tables_before ;

DROP TABLE t1;

SELECT @tmp_tables_after;

@tmp_tables_after

1

SELECT @tmp_tables_before ;

@tmp_tables_before

1

SELECT @tmp_tables_after = @tmp_tables_before ;

@tmp_tables_after = @tmp_tables_before

1

SELECT @tmp_tables_after;

@tmp_tables_after

2

SELECT @tmp_tables_before ;

@tmp_tables_before

1

SELECT @tmp_tables_after = @tmp_tables_before ;

@tmp_tables_after = @tmp_tables_before

0