如何使用动态 SQL (MySQL) 将查询结果存储到局部变量中？

Question

在我编写的过程中，我需要将动态 SQL 查询的结果存储到局部变量中。像这样：

DELIMITER //
CREATE PROCEDURE test_maxsum(uid varchar(25))
BEGIN

    DECLARE maxsum int;
    SET @SQL = CONCAT('SELECT MAX(sum_val) FROM ', uid);
            PREPARE stmt FROM @SQL;
            EXECUTE stmt INTO maxsum;
            DEALLOCATE PREPARE stmt;
    SELECT maxsum;
END//

DELIMITER ;

Answer 1

局部变量不能在预处理语句中赋值。不过，您可以使用 user-defined 变量：

DELIMITER //
CREATE PROCEDURE test_maxsum(uid varchar(25))
BEGIN
    SET @SQL = CONCAT('SELECT MAX(sum_val) INTO @maxsum FROM ', uid);
    PREPARE stmt FROM @SQL;
    EXECUTE stmt;
    DEALLOCATE PREPARE stmt;

    SELECT @maxsum;
END//

DELIMITER ;

如何使用动态 SQL (MySQL) 将查询结果存储到局部变量中？

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