CASE
mysql> SELECT CASE 1 WHEN 1 THEN 'one'
-> WHEN 2 THEN 'two' ELSE 'more' END;
-> 'one'
mysql> SELECT CASE WHEN 1>0 THEN 'true' ELSE 'false' END;
-> 'true'
mysql> SELECT CASE BINARY 'B'
-> WHEN 'a' THEN 1 WHEN 'b' THEN 2 END;
-> NULL
IFNULL
mysql> SELECT IFNULL("TEST", 'OK');
+----------------------+
| IFNULL("TEST", 'OK') |
+----------------------+
| TEST |
+----------------------+
1 row in set (0.00 sec)
mysql> SELECT IFNULL(NULL, 'OK');
+--------------------+
| IFNULL(NULL, 'OK') |
+--------------------+
| OK |
+--------------------+
1 row in set (0.00 sec)
NULLIF()
IF
mysql> SELECT IFNULL("TEST", 'OK');
+----------------------+
| IFNULL("TEST", 'OK') |
+----------------------+
| TEST |
+----------------------+
1 row in set (0.00 sec)
mysql> SELECT IFNULL(NULL, 'OK');
+--------------------+
| IFNULL(NULL, 'OK') |
+--------------------+
| OK |
+--------------------+
1 row in set (0.00 sec)
原文出处：Netkiller 系列 手札
本文作者：陈景峯
转载请与作者联系，同时请务必标明文章原始出处和作者信息及本声明。
