通用合并表存储过程 循环变量与字符连接

存储过程循环变量与字符连接

mysql> DELIMITER $$
mysql> drop PROCEDURE sp_test_switch$$
Query OK, 0 rows affected (0.01 sec)

mysql> CREATE PROCEDURE sp_test_switch()
    -> BEGIN
    ->  declare a int;
    ->  declare b varchar(5000);
    ->  set a=1;
    ->  set b='';
    ->  while a<10 do
    ->          set b = concat(b,',',a);
    ->          set a=a+1;
    ->  end while;
    ->  select b;
    -> END
    -> $$
Query OK, 0 rows affected (0.00 sec)

mysql> DELIMITER ;
mysql>
mysql> call sp_test_switch();
+--------------------+
| b                  |
+--------------------+
| ,1,2,3,4,5,6,7,8,9 |
+--------------------+
1 row in set (0.00 sec)
Query OK, 0 rows affected (0.00 sec)
mysql>

mysql存储过程的变量定义：declare和直接set @var什么区别？

我的理解是, declare定义的是局部变量, 只能用在存储过程或函数中, 其有效区间就是存储过程或函数中声明该变量的begin end区间.而@var属于用户变量(自己声明的), 其有效区间就是该session, 你既可以在存储过程或函数中使用, 也可以在自己写的SQL语句中使用.还有@不需要声明类型，declare必须指定类型

CREATE PROCEDURE sp_starnight_cbj() 
BEGIN
DECLARE A INT DEFAULT 1;
DECLARE B VARCHAR(5000) DEFAULT '';
WHILE A<10 DO
	SET B = CONCAT(B,',',A);
	SET A=A+1;
END WHILE;
SELECT B;
END; 

 应用：所有分表 

DROP PROCEDURE IF EXISTS `merage_branch_table`;
CREATE PROCEDURE `merage_branch_table`(
    IN     p_table_name   VARCHAR(200),    
    IN     p_branch_size  INT,
    in     p_lpad         INT
)
BEGIN
    DECLARE m_begin_row INT DEFAULT 0;
    SET @m_merage_sql = '';
    WHILE m_begin_row<p_branch_size DO
        IF(m_begin_row=p_branch_size-1)
            THEN SET @m_merage_sql = CONCAT(@m_merage_sql, 'SELECT * FROM ', p_table_name, '_', LPAD(m_begin_row, p_lpad, 0));
            ELSE SET @m_merage_sql = CONCAT(@m_merage_sql, 'SELECT * FROM ', p_table_name, '_', LPAD(m_begin_row, p_lpad, 0),' UNION ALL ');
        END IF;

        SET m_begin_row = m_begin_row+1;
    END WHILE;

    PREPARE main_stmt FROM @m_merage_sql;  
    EXECUTE main_stmt;             
END;