在 MYSQL 中编写 WHILE 循环的正确语法

Question

使用 mysql-5.7.30 似乎以下循环语法无效。

mysql> SET @r = 6
    -> SET @i = 3
    -> WHILE @i <= @r DO
    -> BEGIN
    ->    PRINT @i
    -> END WHILE;
ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'SET @i = 3
WHILE @i <= @r DO
BEGIN
   PRINT @i
END WHILE' at line 2
mysql>

我看到了各种格式，例如WHILE i <= r DO 似乎不同的版本，在语法上有细微的差别。我该如何解决？

更新：

我什至根据下面的答案创建了一个程序，但如您所见，它失败了。

mysql> CREATE PROCEDURE dowhile()
    -> BEGIN
    -> DECLARE r INT DEFAULT 4
    -> DECLARE i INT DEFAULT 3
    -> WHILE i <= r DO
    -> SELECT * FROM mdl_user WHERE id=i
    -> END WHILE
    -> END;
ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'DECLARE i INT DEFAULT 3
WHILE i <= r DO
SELECT * FROM mdl_user WHERE id=i
mysql>

更新：

关于分隔符的example，我写了下面的代码，最后却报错

mysql> DELIMITER //
mysql> CREATE PROCEDURE dowhile()
    -> BEGIN
    -> DECLARE r INT DEFAULT 4;
    -> DECLARE i INT DEFAULT 3;
    -> WHILE i <= r DO
    -> SELECT * FROM mdl_user WHERE id=i;
    -> END WHILE;
    -> END //
ERROR 1044 (42000): Access denied for user 'moodleuser'@'localhost' to database 'moodle'

更新：

下面的代码也是错误的

$ mysql -u moodleuser -p moodle
Enter password:
Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

mysql> CREATE PROCEDURE dowhile()
    -> BEGIN
    -> DECLARE r INT DEFAULT 4;
ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near '' at line 3

Answer 1

像WHILE这样的流程控制语句可以在存储程序中使用。另外 WHILE 中的 BEGIN 和 PRINT 用于 SQL Server / Sybase，而不是 MySQL.

请参阅 WHILE

的文档

Answer 2

您在每个语句的末尾缺少分号。此外，您需要在每次迭代之间递增 i（否则它是一个无限循环）。

考虑：

DELIMITER //

CREATE PROCEDURE dowhile()
BEGIN
    DECLARE r INT DEFAULT 4;
    DECLARE i INT DEFAULT 3;
    WHILE i <= r DO
        SELECT * FROM mdl_user WHERE id = i;
        SET i = i + 1;
    END WHILE;
END//

DELIMITER ;

在 MYSQL 中编写 WHILE 循环的正确语法

Correct syntax for writing WHILE loop in MYSQL

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loops

stored-procedures