如何在不使用存储过程的情况下编写在MySql中运行n次的循环.
这是我使用存储过程的方式:
DELIMITER $$
DROP PROCEDURE IF EXISTS test$$
CREATE PROCEDURE test()
BEGIN
DECLARE count INT DEFAULT 0;
WHILE count < 10 DO
/**Sql statement**/
SET count = count + 1;
END WHILE;
END$$
DELIMITER ;
然后我以这种方式执行我的程序:
call test();
如果我删除存储过程并运行正常查询,则失败并显示以下错误:
1064 - 您的SQL语法出错; 检查与MySQL服务器版本对应的手册,以便在'DECLARE count INT DEFAULT 0附近使用正确的语法; 在第2行计数<10 DO
我已经通过互联网查找了没有运气的解决方案.
根据评论编辑:
上面的存储过程完全符合我的要求:它循环10次并执行我的sql语句.现在我想在不使用存储过程的情况下完成同样的事情.就像是:
DECLARE count INT DEFAULT 0;
WHILE count < 10 DO
/**Sql statement**/
SET count = count + 1;
END WHILE;
Vla*_*nov 15
关于流控制语句的 MySQL文档说:
MySQL支持IF,CASE,ITERATE,LEAVE LOOP,WHILE和REPEAT结构,用于存储程序中的流控制.
存储程序和视图的文档说:
存储的程序定义包括可以使用复合语句,循环,条件和声明变量的主体.
本节介绍BEGIN ... END复合语句的语法以及可在存储程序体中使用的其他语句:存储过程和函数,触发器和事件.
复合语句是一个可以包含其他块的块; 变量,条件处理程序和游标的声明; 和流控制结构,如循环和条件测试.
因此,看起来您只能在存储过程,函数或触发器中运行显式循环.
根据您在SQL语句中的操作,可以使用数字表(或视图)(在mysql中创建"数字表",MYSQL:顺序数表).
如果您的查询是a SELECT并且可以将SELECT10次结果作为一个长结果集(而不是10个单独的结果集)返回,则可以执行以下操作:
SELECT MainQuery.*
FROM
(
SELECT 1 AS Number
UNION ALL SELECT 2
UNION ALL SELECT 3
UNION ALL SELECT 4
UNION ALL SELECT 5
UNION ALL SELECT 6
UNION ALL SELECT 7
UNION ALL SELECT 8
UNION ALL SELECT 9
UNION ALL SELECT 10
) AS Numbers
CROSS JOIN
(
SELECT 'some data' AS Result
) AS MainQuery
INSERT的示例
我建议在数据库中有一个永久的数字表.在许多情况下它很有用.请参阅上面的链接如何生成它.
所以,如果你有一个表Numbers的int列Number,其值为1到100K(就像我一样),并且在这一列上有主键,那么代替这个循环:
DECLARE count INT DEFAULT 0;
WHILE count < 10 DO
INSERT INTO table_name(col1,col2,col3)
VALUES("val1","val2",count);
SET count = count + 1;
END WHILE;
你可以写:
INSERT INTO table_name(col1,col2,col3)
SELECT ("val1", "val2", Numbers.Number-1)
FROM Numbers
WHERE Numbers.Number <= 10;
它的工作速度也快了近10倍.
您可以使用MariaDB Sequence Engine直接执行此操作.MariaDB是MySQL的二进制替代品.
"序列引擎允许使用给定的起始值,结束值和增量创建升序或降序数字序列(正整数)."
[手动序列引擎]
以下是一些示例:
mysql -uroot -p
Enter password: xxxxxxx
Welcome to the MariaDB monitor. Commands end with ; or \g.
Your MariaDB connection id is 5
Server version: 10.0.20-MariaDB-log Homebrew
Copyright (c) 2000, 2015, Oracle, MariaDB Corporation Ab and others.
Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.
MariaDB [(none)]> use tmp
Database changed
MariaDB [tmp]> select version();
+---------------------+
| version() |
+---------------------+
| 10.0.20-MariaDB-log |
+---------------------+
1 row in set (0.00 sec)
MariaDB [tmp]> select * from seq_1_to_10;
+-----+
| seq |
+-----+
| 1 |
| 2 |
| 3 |
| 4 |
| 5 |
| 6 |
| 7 |
| 8 |
| 9 |
| 10 |
+-----+
10 rows in set (0.00 sec)
MariaDB [tmp]> select * from seq_1_to_10_step_2;
+-----+
| seq |
+-----+
| 1 |
| 3 |
| 5 |
| 7 |
| 9 |
+-----+
5 rows in set (0.00 sec)
MariaDB [tmp]> SELECT DAYNAME('1980-12-05' + INTERVAL (seq) YEAR) day,
-> '1980-12-05' + INTERVAL (seq) YEAR date FROM seq_0_to_40;
+-----------+------------+
| day | date |
+-----------+------------+
| Friday | 1980-12-05 |
| Saturday | 1981-12-05 |
| Sunday | 1982-12-05 |
| Monday | 1983-12-05 |
| Wednesday | 1984-12-05 |
| Thursday | 1985-12-05 |
| Friday | 1986-12-05 |
| Saturday | 1987-12-05 |
| Monday | 1988-12-05 |
| Tuesday | 1989-12-05 |
| Wednesday | 1990-12-05 |
| Thursday | 1991-12-05 |
| Saturday | 1992-12-05 |
| Sunday | 1993-12-05 |
| Monday | 1994-12-05 |
| Tuesday | 1995-12-05 |
| Thursday | 1996-12-05 |
| Friday | 1997-12-05 |
| Saturday | 1998-12-05 |
| Sunday | 1999-12-05 |
| Tuesday | 2000-12-05 |
| Wednesday | 2001-12-05 |
| Thursday | 2002-12-05 |
| Friday | 2003-12-05 |
| Sunday | 2004-12-05 |
| Monday | 2005-12-05 |
| Tuesday | 2006-12-05 |
| Wednesday | 2007-12-05 |
| Friday | 2008-12-05 |
| Saturday | 2009-12-05 |
| Sunday | 2010-12-05 |
| Monday | 2011-12-05 |
| Wednesday | 2012-12-05 |
| Thursday | 2013-12-05 |
| Friday | 2014-12-05 |
| Saturday | 2015-12-05 |
| Monday | 2016-12-05 |
| Tuesday | 2017-12-05 |
| Wednesday | 2018-12-05 |
| Thursday | 2019-12-05 |
| Saturday | 2020-12-05 |
+-----------+------------+
41 rows in set (0.00 sec)
MariaDB [tmp]>
这里有一个示例:
MariaDB [(none)]> use tmp
Database changed
MariaDB [tmp]> SELECT * FROM seq_1_to_5,
-> (SELECT * FROM animals) AS x
-> ORDER BY seq;
+-----+------+-----------+-----------------+
| seq | id | name | specie |
+-----+------+-----------+-----------------+
| 1 | 1 | dougie | dog-poodle |
| 1 | 6 | tweety | bird-canary |
| 1 | 5 | spotty | turtle-spotted |
| 1 | 4 | mr.turtle | turtle-snapping |
| 1 | 3 | cadi | cat-persian |
| 1 | 2 | bonzo | dog-pitbull |
| 2 | 4 | mr.turtle | turtle-snapping |
| 2 | 3 | cadi | cat-persian |
| 2 | 2 | bonzo | dog-pitbull |
| 2 | 1 | dougie | dog-poodle |
| 2 | 6 | tweety | bird-canary |
| 2 | 5 | spotty | turtle-spotted |
| 3 | 6 | tweety | bird-canary |
| 3 | 5 | spotty | turtle-spotted |
| 3 | 4 | mr.turtle | turtle-snapping |
| 3 | 3 | cadi | cat-persian |
| 3 | 2 | bonzo | dog-pitbull |
| 3 | 1 | dougie | dog-poodle |
| 4 | 2 | bonzo | dog-pitbull |
| 4 | 1 | dougie | dog-poodle |
| 4 | 6 | tweety | bird-canary |
| 4 | 5 | spotty | turtle-spotted |
| 4 | 4 | mr.turtle | turtle-snapping |
| 4 | 3 | cadi | cat-persian |
| 5 | 5 | spotty | turtle-spotted |
| 5 | 4 | mr.turtle | turtle-snapping |
| 5 | 3 | cadi | cat-persian |
| 5 | 2 | bonzo | dog-pitbull |
| 5 | 1 | dougie | dog-poodle |
| 5 | 6 | tweety | bird-canary |
+-----+------+-----------+-----------------+
30 rows in set (0.00 sec)
MariaDB [tmp]>
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