變量定義:
DECLARE variable_name [,variable_name...] datatype [DEFAULT value];
其中,datatype爲mysql的數據類型,如:INT, FLOAT, DATE, VARCHAR(length)
例:
DECLARE l_int INT unsigned default 4000000;
DECLARE l_numeric NUMERIC(8,2) DEFAULT 9.95;
DECLARE l_date DATE DEFAULT '1999-12-31';
DECLARE l_datetime DATETIME DEFAULT '1999-12-31 23:59:59';
DECLARE l_varchar VARCHAR(255) DEFAULT 'This will not be padded';
變量賦值
SET 變量名 = 表達式值 [,variable_name = expression ...]
參數
mysql存儲過程的參數用在存儲過程的定義,共有三種參數類型,IN,OUT,INOUT
Create procedure|function([[IN |OUT |INOUT ] 參數名 數據類形...])
IN 輸入參數
表示該參數的值必須在調用存儲過程時指定,在存儲過程中修改該參數的值不能被返回,爲默認值
OUT 輸出參數
該值可在存儲過程內部被改變,並可返回
INOUT 輸入輸出參數
調用時指定,並且可被改變和返回
IN參數例子:
創建
mysql> CREATE PROCEDURE sp_demo_in_parameter(IN p_in INT)
mysql> BEGIN SELECT p_in; /*查詢輸入參數*/
mysql> SET p_in=2; /*修改*/
mysq> select p_in; /*查看修改後的值*/
mysql> END;
執行結果:
mysql> set @p_in=1;
mysql> call sp_demo_in_parameter(@p_in);
+------+
| p_in |
+------+
| 1 |
+------+
+------+
| p_in |
+------+
| 2 |
+------+
mysql> select @p_in;
+-------+
| @p_in |
+-------+
| 1 |
+-------+
以上可以看出,p_in雖然在存儲過程中被修改,但並不影響@p_id的值
OUT參數例子
創建:
mysql> CREATE PROCEDURE sp_demo_out_parameter(OUT p_out INT)
mysql> BEGIN SELECT p_out;/*查看輸出參數*/
mysql> SET p_out=2;/*修改參數值*/
mysql> SELECT p_out;/*看看有否變化*/
mysql> END;
執行結果:
mysql> SET @p_out=1;
mysql> CALL sp_demo_out_parameter(@p_out);
+-------+
| p_out |
+-------+
| NULL |
+-------+
/*未被定義,返回NULL*/
+-------+
| p_out |
+-------+
| 2 |
+-------+
mysql> SELECT @p_out;
+-------+
| p_out |
+-------+
| 2 |
+----------+
INOUT參數例子:
mysql> CREATE PROCEDURE sp_demo_inout_parameter(INOUT p_inout INT)
mysql> BEGIN SELECT p_inout;
mysql> SET p_inout=2;
mysql> SELECT p_inout; END;
執行結果:
set @p_inout=1
call sp_demo_inout_parameter(@p_inout) //
+---------+
| p_inout |
+---------+
| 1 |
+---------+
+---------+
| p_inout |
+---------+
| 2 |
+---------+
select @p_inout;
+----------+
| @p_inout |
+----------+
| 2 |
+----------+
用戶變量
1、 在mysql客戶端使用用戶變量
mysql> SELECT 'Hello World' into @x;
mysql> SELECT @x;
+-------------+
| @x |
+-------------+
| Hello World |
+-------------+
mysql> SET @y='Goodbye Cruel World';
mysql> select @y;
+---------------------+
| @y |
+---------------------+
| Goodbye Cruel World |
+---------------------+
mysql> SET @z=1+2+3;
mysql> select @z;
+------+
| @z |
+------+
| 6 |
+------+
2、 在存儲過程中使用用戶變量
mysql> CREATE PROCEDURE GreetWorld( ) SELECT CONCAT(@greeting,' World');
mysql> SET @greeting='Hello';
mysql> CALL GreetWorld( );
+----------------------------+
| CONCAT(@greeting,' World') |
+----------------------------+
| Hello World |
+----------------------------+
3、 在存儲過程間傳遞全局範圍的用戶變量
mysql> CREATE PROCEDURE p1( ) SET @last_procedure='p1';
mysql> CREATE PROCEDURE p2( ) SELECT CONCAT('Last procedure was ',@last_procedure);
mysql> CALL p1( );
mysql> CALL p2( );
+-----------------------------------------------+
| CONCAT('Last procedure was ',@last_procedure) |
+-----------------------------------------------+
| Last procedure was p1 |
+-----------------------------------------------+
注意:
①用戶變量名一般以@開頭
②濫用用戶變量會導致程序難以理解及管理
註釋
mysql存儲過程可使用兩種風格的註釋
雙模槓:--
該風格一般用於單行註釋
c風格:/* 註釋內容 */ 一般用於多行註釋