MySQL外鍵

Question

在其他兩個表上，我將d_desavanja-> id字段設置爲外鍵，但在此表上，我不能。

我該如何讓它工作？

SQL query: 

ALTER TABLE `d_des_kat` ADD FOREIGN KEY ( `desavanje_id`) REFERENCES `desavanja`.`d_desavanja` (

`id` 
) ON DELETE CASCADE ON UPDATE CASCADE ; 

MySQL said: 

#1452 - Cannot add or update a child row: a foreign key constraint fails (`desavanja/#sql-12f3_5af2e`, CONSTRAINT `#sql-12f3_5af2e_ibfk_1` FOREIGN KEY (`desavanje_id`) REFERENCES `d_desavanja` (`id`) ON DELETE CASCADE ON UPDATE CASCADE) 

Answer 1

您在d_des_kat中有一行，該約束失敗。檢查您的數據以確保所有非NULL d_des_kat.desavanje_id值與d_desavanja中的現有id相匹配。

下面的查詢應該表現出你的違規行：

SELECT * 
FROM d_des_kat 
WHERE desavanje_id NOT IN (SELECT id FROM d_desavanja)