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--流程函数。if ，ifnull ，case 语句！mysql> create table sal (id int,sal decimal (9,2));
Query OK, 0 rows affected (0.06 sec) mysql> insert into sal values (1,1000),(2,2000),(3,3000),(4,4000),(5,null); Query OK, 5 rows affected (0.01 sec) Records: 5 Duplicates: 0 Warnings: 0--if(EXP,T,F) EXP 为真则返回T,EXP为假，则返回Fmysql> select * from sal; +------+---------+ | id | sal | +------+---------+ | 1 | 1000.00 | | 2 | 2000.00 | | 3 | 3000.00 | | 4 | 4000.00 | | 5 | NULL | +------+---------+ 5 rows in set (0.00 sec)mysql> select id, if(sal > 3000,'high','low') from sal;
+------+-----------------------------+ | id | if(sal > 3000,'high','low') | +------+-----------------------------+ | 1 | low | | 2 | low | | 3 | low | | 4 | high | | 5 | low |--这里null >3000 为假！+------+-----------------------------+ 5 rows in set (0.01 sec)--IFNULL(VAL,N)如果val 为null 则返回Nmysql> select id, ifnull(sal,0) from sal; +------+---------------+ | id | ifnull(sal,0) | +------+---------------+ | 1 | 1000.00 | | 2 | 2000.00 | | 3 | 3000.00 | | 4 | 4000.00 | | 5 | 0.00 | +------+---------------+ 5 rows in set (0.01 sec)--case 语句和oracle的一样了！mysql> select case when sal<=3000 then 'low' else 'high' end from sal; +------------------------------------------------+ | case when sal<=3000 then 'low' else 'high' end | +------------------------------------------------+ | low | | low | | low | | high | | high | +------------------------------------------------+ 5 rows in set (0.00 sec) mysql> select id, case sal when 2000 then 'low' when 3000 then 'mid' else 'high' end from sal; +------+--------------------------------------------------------------------+ | id | case sal when 2000 then 'low' when 3000 then 'mid' else 'high' end | +------+--------------------------------------------------------------------+ | 1 | high | | 2 | low | | 3 | mid | | 4 | high | | 5 | high | +------+--------------------------------------------------------------------+ 5 rows in set (0.01 sec)这里只是简单介绍，跟多的需要在实践中学习！抛砖引玉了，呵呵
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