mysql在存储过程中判断某一数据是否存在

DELIMITER //
 
CREATE PROCEDURE CheckAndInsert()
BEGIN
    DECLARE exists INT DEFAULT 0;
    
    -- 检查数据是否存在
    SELECT COUNT(*) INTO exists FROM your_table WHERE some_column = 'some_value';
    
    IF exists = 0 THEN
        INSERT INTO your_table (column1, column2) VALUES ('value1', 'value2');
    ELSE
        -- 数据已存在时的操作，例如更新或提示信息
        UPDATE your_table SET column2 = 'new_value' WHERE some_column = 'some_value';
    END IF;
END //
 
DELIMITER ;

方法二

DELIMITER //
 
CREATE PROCEDURE CheckAndDelete()
BEGIN
    DECLARE exists INT DEFAULT 0;
    
    -- 检查数据是否存在
    SELECT COUNT(*) INTO exists FROM your_table WHERE some_column = 'some_value';
    
    IF exists > 0 THEN
        DELETE FROM your_table WHERE some_column = 'some_value';
    ELSE
        -- 数据不存在的操作，例如提示信息
        SELECT 'Data does not exist' AS message;
    END IF;
END //
 
DELIMITER ;

方法三

DELIMITER //
 
CREATE PROCEDURE CheckAndDelete()
BEGIN
    DELETE FROM your_table WHERE some_column = 'some_value' AND NOT EXISTS (
        SELECT 1 FROM your_table WHERE some_column = 'some_value' AND another_column = 'another_value'
    );
END //
 
DELIMITER ;

标签：mysql