mysql数据库条件判断查询语句的常见写法说明

大家都知道只有的了mysql 5后才出现了存储过程，这些用法，那么我们要在sql 中用if else while这些，就得用存过程或函数来实例了。 mysql DELIMITER // mysql CREATE FUNCTION myFunction (quantity INT(10)) RETURNS INT(10) - BEGIN - - WHILE quantity MO

大家都知道只有的了mysql 5后才出现了存储过程，，这些用法，那么我们要在sql 中用if else while这些，就得用存过程或函数来实例了。

mysql> DELIMITER //
mysql> CREATE FUNCTION myFunction (quantity INT(10)) RETURNS INT(10)
-> BEGIN
->
-> WHILE quantity MOD 12 > 0 DO
-> SET quantity = quantity + 1;
-> END WHILE;
->
-> RETURN quantity;
->
-> END
-> //
Query OK, 0 rows affected (0.00 sec)

mysql> DELIMITER ;
mysql>
mysql> select myFunction(10);
+----------------+
| myFunction(10) |
+----------------+
| 12 |
+----------------+
1 row in set (0.00 sec)

mysql>
mysql> select myFunction(24);
+----------------+
| myFunction(24) |
+----------------+
| 24 |
+----------------+
1 row in set (0.00 sec)

实例二

mysql> delimiter //
mysql> create procedure test_while (IN in_count INT)
-> BEGIN
-> declare count INT default 0;
->
-> while count -> set count = count + 1;
-> end while;
->
-> select count;
-> END
-> //
Query OK, 0 rows affected (0.00 sec)

mysql>
mysql> delimiter ;
mysql>
mysql> call test_while(10);
+-------+
| count |
+-------+
| 10 |
+-------+
1 row in set (0.00 sec)

Query OK, 0 rows affected (0.00 sec)

带有条件判断的

mysql> delimiter $$
mysql>
mysql> CREATE PROCEDURE myProc()
-> BEGIN
->
-> DECLARE i int;
-> SET i=1;
-> loop1: WHILE i -> IF MOD(i,2)0 THEN /*Even number - try again*/
-> SELECT CONCAT(i," is an odd number");
-> END IF;
-> SET i=i+1;
-> END WHILE loop1;
-> END$$
Query OK, 0 rows affected (0.00 sec)

mysql>
mysql> delimiter ;
mysql> call myProc();
+-------------------------------+
| CONCAT(i," is an odd number") |
+-------------------------------+
| 1 is an odd number |
+-------------------------------+
1 row in set (0.02 sec)

+-------------------------------+
| CONCAT(i," is an odd number") |
+-------------------------------+
| 3 is an odd number |
+-------------------------------+
1 row in set (0.02 sec)

+-------------------------------+
| CONCAT(i," is an odd number") |
+-------------------------------+
| 5 is an odd number |
+-------------------------------+
1 row in set (0.02 sec)

+-------------------------------+
| CONCAT(i," is an odd number") |
+-------------------------------+
| 7 is an odd number |
+-------------------------------+
1 row in set (0.02 sec)

+-------------------------------+
| CONCAT(i," is an odd number") |
+-------------------------------+
| 9 is an odd number |
+-------------------------------+
1 row in set (0.02 sec)

Query OK, 0 rows affected (0.38 sec)