MySQL外鍵問題

Question

我在MySQL 5.5.8上運行該錯誤

Mysql2::Error: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'WHERE 
      (SELECT id FROM products WHERE id = NEW.brand_id) IS NULL;
      EN' at line 6:  
    CREATE TRIGGER fk_brands_products_insert 
    BEFORE INSERT ON brands 
    FOR EACH ROW BEGIN
    SELECT 
      RAISE(ABORT, "constraint violation: fk_brands_products")
    WHERE 
      (SELECT id FROM products WHERE id = NEW.brand_id) IS NULL;
      END;

有什么事嗎

Answer 1

您確定可以在這樣的查詢中引發錯誤嗎？ 我在任何地方都找不到。 我認為正確的方法是選擇一個COUNT或EXISTS並將該結果返回到變量中。 然后，在查詢之后，如果結果不符合您的期望，則會引發錯誤。

像這樣：

SELECT count(id) INTO IDCOUNT FROM products WHERE id = NEW.brand_id;

僅僅添加一個真正的約束會更好嗎？ 還是使用不支持該類型的存儲類型？

Answer 2

我懷疑問題出在您的select語句中沒有FROM子句。