drop table if exists t1;
select CASE "b" when "a" then 1 when "b" then 2 END;
CASE "b" when "a" then 1 when "b" then 2 END
2
select CASE "c" when "a" then 1 when "b" then 2 END;
CASE "c" when "a" then 1 when "b" then 2 END
NULL
select CASE "c" when "a" then 1 when "b" then 2 ELSE 3 END;
CASE "c" when "a" then 1 when "b" then 2 ELSE 3 END
3
select CASE BINARY "b" when "a" then 1 when "B" then 2 WHEN "b" then "ok" END;
CASE BINARY "b" when "a" then 1 when "B" then 2 WHEN "b" then "ok" END
ok
select CASE "b" when "a" then 1 when binary "B" then 2 WHEN "b" then "ok" END;
CASE "b" when "a" then 1 when binary "B" then 2 WHEN "b" then "ok" END
ok
select CASE concat("a","b") when concat("ab","") then "a" when "b" then "b" end;
CASE concat("a","b") when concat("ab","") then "a" when "b" then "b" end
a
select CASE when 1=0 then "true" else "false" END;
CASE when 1=0 then "true" else "false" END
false
select CASE 1 when 1 then "one" WHEN 2 then "two" ELSE "more" END;
CASE 1 when 1 then "one" WHEN 2 then "two" ELSE "more" END
one
explain extended select CASE 1 when 1 then "one" WHEN 2 then "two" ELSE "more" END;
id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
1	SIMPLE	NULL	NULL	NULL	NULL	NULL	NULL	NULL	No tables used
Warnings:
Note	1003	select (case 1 when 1 then _latin1'one' when 2 then _latin1'two' else _latin1'more' end) AS `CASE 1 when 1 then "one" WHEN 2 then "two" ELSE "more" END`
select CASE 2.0 when 1 then "one" WHEN 2.0 then "two" ELSE "more" END;
CASE 2.0 when 1 then "one" WHEN 2.0 then "two" ELSE "more" END
two
select (CASE "two" when "one" then "1" WHEN "two" then "2" END) | 0;
(CASE "two" when "one" then "1" WHEN "two" then "2" END) | 0
2
select (CASE "two" when "one" then 1.00 WHEN "two" then 2.00 END) +0.0;
(CASE "two" when "one" then 1.00 WHEN "two" then 2.00 END) +0.0
2.00
select case 1/0 when "a" then "true" else "false" END;
case 1/0 when "a" then "true" else "false" END
false
select case 1/0 when "a" then "true" END;
case 1/0 when "a" then "true" END
NULL
select (case 1/0 when "a" then "true" END) | 0;
(case 1/0 when "a" then "true" END) | 0
NULL
select (case 1/0 when "a" then "true" END) + 0.0;
(case 1/0 when "a" then "true" END) + 0.0
NULL
select case when 1>0 then "TRUE" else "FALSE" END;
case when 1>0 then "TRUE" else "FALSE" END
TRUE
select case when 1<0 then "TRUE" else "FALSE" END;
case when 1<0 then "TRUE" else "FALSE" END
FALSE
create table t1 (a int);
insert into t1 values(1),(2),(3),(4);
select case a when 1 then 2 when 2 then 3 else 0 end as fcase, count(*) from t1 group by fcase;
fcase	count(*)
0	2
2	1
3	1
explain extended select case a when 1 then 2 when 2 then 3 else 0 end as fcase, count(*) from t1 group by fcase;
id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
1	SIMPLE	t1	ALL	NULL	NULL	NULL	NULL	4	Using temporary; Using filesort
Warnings:
Note	1003	select (case `test`.`t1`.`a` when 1 then 2 when 2 then 3 else 0 end) AS `fcase`,count(0) AS `count(*)` from `test`.`t1` group by (case `test`.`t1`.`a` when 1 then 2 when 2 then 3 else 0 end)
select case a when 1 then "one" when 2 then "two" else "nothing" end as fcase, count(*) from t1 group by fcase;
fcase	count(*)
nothing	2
one	1
two	1
drop table t1;
create table t1 (row int not null, col int not null, val varchar(255) not null);
insert into t1 values (1,1,'orange'),(1,2,'large'),(2,1,'yellow'),(2,2,'medium'),(3,1,'green'),(3,2,'small');
select max(case col when 1 then val else null end) as color from t1 group by row;
color
orange
yellow
green
drop table t1;
SET NAMES latin1;
CREATE TABLE t1 SELECT 
CASE WHEN 1 THEN _latin1'a' COLLATE latin1_danish_ci ELSE _latin1'a' END AS c1,
CASE WHEN 1 THEN _latin1'a' ELSE _latin1'a' COLLATE latin1_danish_ci END AS c2,
CASE WHEN 1 THEN 'a' ELSE  1  END AS c3,
CASE WHEN 1 THEN  1  ELSE 'a' END AS c4,
CASE WHEN 1 THEN 'a' ELSE 1.0 END AS c5,
CASE WHEN 1 THEN 1.0 ELSE 'a' END AS c6,
CASE WHEN 1 THEN  1  ELSE 1.0 END AS c7,
CASE WHEN 1 THEN 1.0 ELSE  1  END AS c8,
CASE WHEN 1 THEN 1.0 END AS c9,
CASE WHEN 1 THEN 0.1e1 else 0.1 END AS c10,
CASE WHEN 1 THEN 0.1e1 else 1 END AS c11,
CASE WHEN 1 THEN 0.1e1 else '1' END AS c12
;
SHOW CREATE TABLE t1;
Table	Create Table
t1	CREATE TABLE `t1` (
  `c1` varchar(1) character set latin1 collate latin1_danish_ci NOT NULL default '',
  `c2` varchar(1) character set latin1 collate latin1_danish_ci NOT NULL default '',
  `c3` varbinary(1) NOT NULL default '',
  `c4` varbinary(1) NOT NULL default '',
  `c5` varbinary(4) NOT NULL default '',
  `c6` varbinary(4) NOT NULL default '',
  `c7` decimal(2,1) NOT NULL default '0.0',
  `c8` decimal(2,1) NOT NULL default '0.0',
  `c9` decimal(2,1) default NULL,
  `c10` double NOT NULL default '0',
  `c11` double NOT NULL default '0',
  `c12` varbinary(5) NOT NULL default ''
) ENGINE=MyISAM DEFAULT CHARSET=latin1
DROP TABLE t1;
SELECT CASE 
WHEN 1 
THEN _latin1'a' COLLATE latin1_danish_ci 
ELSE _latin1'a' COLLATE latin1_swedish_ci
END;
ERROR HY000: Illegal mix of collations (latin1_danish_ci,EXPLICIT) and (latin1_swedish_ci,EXPLICIT) for operation 'case'
SELECT CASE _latin1'a' COLLATE latin1_general_ci
WHEN _latin1'a' COLLATE latin1_danish_ci  THEN 1
WHEN _latin1'a' COLLATE latin1_swedish_ci THEN 2
END;
ERROR HY000: Illegal mix of collations (latin1_general_ci,EXPLICIT), (latin1_danish_ci,EXPLICIT), (latin1_swedish_ci,EXPLICIT) for operation 'case'
SELECT 
CASE _latin1'a' COLLATE latin1_general_ci  WHEN _latin1'A' THEN '1' ELSE 2 END,
CASE _latin1'a' COLLATE latin1_bin         WHEN _latin1'A' THEN '1' ELSE 2 END,
CASE _latin1'a' WHEN _latin1'A' COLLATE latin1_swedish_ci THEN '1' ELSE 2 END,
CASE _latin1'a' WHEN _latin1'A' COLLATE latin1_bin        THEN '1' ELSE 2 END
;
CASE _latin1'a' COLLATE latin1_general_ci  WHEN _latin1'A' THEN '1' ELSE 2 END	CASE _latin1'a' COLLATE latin1_bin         WHEN _latin1'A' THEN '1' ELSE 2 END	CASE _latin1'a' WHEN _latin1'A' COLLATE latin1_swedish_ci THEN '1' ELSE 2 END	CASE _latin1'a' WHEN _latin1'A' COLLATE latin1_bin        THEN '1' ELSE 2 END
1	2	1	2
CREATE TABLE t1 SELECT COALESCE(_latin1'a',_latin2'a');
ERROR HY000: Illegal mix of collations (latin1_swedish_ci,COERCIBLE) and (latin2_general_ci,COERCIBLE) for operation 'coalesce'
CREATE TABLE t1 SELECT COALESCE('a' COLLATE latin1_swedish_ci,'b' COLLATE latin1_bin);
ERROR HY000: Illegal mix of collations (latin1_swedish_ci,EXPLICIT) and (latin1_bin,EXPLICIT) for operation 'coalesce'
CREATE TABLE t1 SELECT 
COALESCE(1), COALESCE(1.0),COALESCE('a'),
COALESCE(1,1.0), COALESCE(1,'1'),COALESCE(1.1,'1'),
COALESCE('a' COLLATE latin1_bin,'b');
explain extended SELECT 
COALESCE(1), COALESCE(1.0),COALESCE('a'),
COALESCE(1,1.0), COALESCE(1,'1'),COALESCE(1.1,'1'),
COALESCE('a' COLLATE latin1_bin,'b');
id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
1	SIMPLE	NULL	NULL	NULL	NULL	NULL	NULL	NULL	No tables used
Warnings:
Note	1003	select coalesce(1) AS `COALESCE(1)`,coalesce(1.0) AS `COALESCE(1.0)`,coalesce(_latin1'a') AS `COALESCE('a')`,coalesce(1,1.0) AS `COALESCE(1,1.0)`,coalesce(1,_latin1'1') AS `COALESCE(1,'1')`,coalesce(1.1,_latin1'1') AS `COALESCE(1.1,'1')`,coalesce((_latin1'a' collate latin1_bin),_latin1'b') AS `COALESCE('a' COLLATE latin1_bin,'b')`
SHOW CREATE TABLE t1;
Table	Create Table
t1	CREATE TABLE `t1` (
  `COALESCE(1)` int(1) NOT NULL default '0',
  `COALESCE(1.0)` decimal(2,1) NOT NULL default '0.0',
  `COALESCE('a')` varchar(1) NOT NULL default '',
  `COALESCE(1,1.0)` decimal(2,1) NOT NULL default '0.0',
  `COALESCE(1,'1')` varbinary(1) NOT NULL default '',
  `COALESCE(1.1,'1')` varbinary(4) NOT NULL default '',
  `COALESCE('a' COLLATE latin1_bin,'b')` varchar(1) character set latin1 collate latin1_bin NOT NULL default ''
) ENGINE=MyISAM DEFAULT CHARSET=latin1
DROP TABLE t1;
SELECT 'case+union+test'
UNION 
SELECT CASE LOWER('1') WHEN LOWER('2') THEN 'BUG' ELSE 'nobug' END;
case+union+test
case+union+test
nobug
SELECT CASE LOWER('1') WHEN LOWER('2') THEN 'BUG' ELSE 'nobug' END;
CASE LOWER('1') WHEN LOWER('2') THEN 'BUG' ELSE 'nobug' END
nobug
SELECT 'case+union+test'
UNION 
SELECT CASE '1' WHEN '2' THEN 'BUG' ELSE 'nobug' END;
case+union+test
case+union+test
nobug
create table t1(a float, b int default 3);
insert into t1 (a) values (2), (11), (8);
select min(a), min(case when 1=1 then a else NULL end),
min(case when 1!=1 then NULL else a end) 
from t1 where b=3 group by b;
min(a)	min(case when 1=1 then a else NULL end)	min(case when 1!=1 then NULL else a end)
2	2	2
drop table t1;
CREATE TABLE t1 (EMPNUM INT);
INSERT INTO t1 VALUES (0), (2);
CREATE TABLE t2 (EMPNUM DECIMAL (4, 2));
INSERT INTO t2 VALUES (0.0), (9.0);
SELECT COALESCE(t2.EMPNUM,t1.EMPNUM) AS CEMPNUM,
t1.EMPNUM AS EMPMUM1, t2.EMPNUM AS EMPNUM2
FROM t1 LEFT JOIN t2 ON t1.EMPNUM=t2.EMPNUM;
CEMPNUM	EMPMUM1	EMPNUM2
0.00	0	0.00
2.00	2	NULL
SELECT IFNULL(t2.EMPNUM,t1.EMPNUM) AS CEMPNUM,
t1.EMPNUM AS EMPMUM1, t2.EMPNUM AS EMPNUM2
FROM t1 LEFT JOIN t2 ON t1.EMPNUM=t2.EMPNUM;
CEMPNUM	EMPMUM1	EMPNUM2
0.00	0	0.00
2.00	2	NULL
DROP TABLE t1,t2;
