sql如果不存在（）插入不起作用

Question

This is my query:

IF NOT EXISTS (SELECT * 
               FROM   teovecerdi 
               WHERE  LocationName = 'Frankfurt' 
               AND    StartDate = '14/02/2015' 
               AND    EndDate = '17/02/2015' 
               AND    Price = '2700') 
INSERT INTO teovecerdi(LocationName, StartDate, EndDate, Price)
VALUES(?,?,?,?)

Can you tell me what's wrong with it? I've also tried with BEGIN and END and it still gives me an error.

EDIT: I handle the parameters correctly.

Answer 1

You can't use an IF statement in a query, it can only be used in a stored procedure.

If you want to do a conditional INSERT , you can use a SELECT query that only returns a row when the condition is met.

INSERT INTO teovecerdi(LocationName, StartDate, EndDate, Price)
SELECT ?, ?, ?, ?
FROM DUAL
WHERE NOT EXISTS (SELECT * 
    FROM   teovecerdi 
    WHERE  LocationName = 'Frankfurt' 
    AND    StartDate = '14/02/2015' 
    AND    EndDate = '17/02/2015' 
    AND    Price = '2700')

Answer 2

您不能在查询或脚本中使用MySQL的过程语法（包括IF这样的语句，以及迭代构造等）。

Answer 3

I am going to suggest a different approach. My guess is that you want LocationName, StartDate, EndDate, Price to be unique. So, let the database do the work for you:

CREATE UNIQUE INDEX unq_teovecerdi_4 on teovecerdi(LocationName, StartDate, EndDate, Price);

Then just be careful to "ignore" errors when you do an insert. My preferred method is:

INSERT INTO teovecerdi (LocationName, StartDate, EndDate, Price)
    VALUES (?, ?, ?, ?)
    ON DUPLICATE KEY UPDATE LocationName = VALUES(LocationName);

The ON DUPLICATE KEY does nothing except absorb the error, when you attempt to insert a duplicate.