Question

如果我提供的名称值不存在，我想在我的客户表中的行中插入值，经过一些搜索，我使用这个SQL查询来做它并且它不起作用：（

IF NOT EXISTS (SELECT Name FROM customer WHERE Name = 'Riyafa') 
INSERT INTO customer (`Name`, `Address`, `ContactNo`,`Total_amout`)
                      VALUES ('Riyafa', 'ABC', '555','1000');

请告诉我为什么这不正确。

Answer 1

if语句仅在存储过程，函数和触发器中允许。一种方法是：

INSERT INTO customer (`Name`, `Address`, `ContactNo`,`Total_amout`)
    SELECT name, address, contactno, total_amount
    FROM (SELECT 'Riyafa' as name, 'ABC' as address, '555' as contact no, '1000' as total_amount) t
    WHERE NOT EXISTS (SELECT 1 FROM customer c WHERE c.name = t.name);

然而，更好的方法是让数据库对名称强制执行唯一性。首先创建一个唯一的索引或名称：

CREATE UNIQUE INDEX idx_customer_name ON customer(name);

然后使用on duplicate key update：

等构造

INSERT INTO customer (`Name`, `Address`, `ContactNo`,`Total_amout`)
    SELECT 'Riyafa' as name, 'ABC' as address, '555' as contact no, '1000' as total_amount
    ON DUPLICATE KEY UPDATE Name = VALUES(Name);

表达式ON DUPLICATE KEY UPDATE Name = VALUES(Name)实际上没有做任何事情，但它会阻止INSERT返回错误。

如果字段值尚不存在，请插入表中

1 个答案: