select * from (select * from t1 union all select * from t1 limit 2) a;
a b
1 a
2 b
explain select * from (select * from t1 union select * from t1) a;
explain select * from (select * from t1 union select * from t1) a;
id select_type table type possible_keys key key_len ref rows Extra
id select_type table type possible_keys key key_len ref rows Extra
1 PRIMARY <derived2> ALL NULL NULL NULL NULL 3
1 PRIMARY <derived2> ALL NULL NULL NULL NULL 3
...
@@ -258,17 +262,13 @@ ID int(11) default NULL,
...
@@ -258,17 +262,13 @@ ID int(11) default NULL,
PARID int(11) default NULL,
PARID int(11) default NULL,
UNIQUE KEY t2_ID_IDX (ID),
UNIQUE KEY t2_ID_IDX (ID),
KEY t2_PARID_IDX (PARID)
KEY t2_PARID_IDX (PARID)
) TYPE=MyISAM DEFAULT CHARSET=latin1;
) engine=MyISAM DEFAULT CHARSET=latin1;
Warnings:
Warning 1286 'TYPE=database_engine' is deprecated. Use 'ENGINE=database_engine' instead.
INSERT INTO t2 VALUES (1000,0),(1001,0),(1002,0),(1003,0),(1008,1),(1009,1),(1010,1),(1011,1),(1016,2);
INSERT INTO t2 VALUES (1000,0),(1001,0),(1002,0),(1003,0),(1008,1),(1009,1),(1010,1),(1011,1),(1016,2);
CREATE TABLE t3 (
CREATE TABLE t3 (
ID int(11) default NULL,
ID int(11) default NULL,
DATA decimal(10,2) default NULL,
DATA decimal(10,2) default NULL,
UNIQUE KEY t3_ID_IDX (ID)
UNIQUE KEY t3_ID_IDX (ID)
) TYPE=MyISAM DEFAULT CHARSET=latin1;
) engine=MyISAM DEFAULT CHARSET=latin1;
Warnings:
Warning 1286 'TYPE=database_engine' is deprecated. Use 'ENGINE=database_engine' instead.
INSERT INTO t3 VALUES (1000,0.00),(1001,0.25),(1002,0.50),(1003,0.75),(1008,1.00),(1009,1.25),(1010,1.50),(1011,1.75);
INSERT INTO t3 VALUES (1000,0.00),(1001,0.25),(1002,0.50),(1003,0.75),(1008,1.00),(1009,1.25),(1010,1.50),(1011,1.75);
select 497, TMP.ID, NULL from (select 497 as ID, MAX(t3.DATA) as DATA from t1 join t2 on (t1.ObjectID = t2.ID) join t3 on (t1.ObjectID = t3.ID) group by t2.ParID order by DATA DESC) as TMP;
select 497, TMP.ID, NULL from (select 497 as ID, MAX(t3.DATA) as DATA from t1 join t2 on (t1.ObjectID = t2.ID) join t3 on (t1.ObjectID = t3.ID) group by t2.ParID order by DATA DESC) as TMP;