插入记录如果在sql中不存在,则重复列名

Question

我想要一个解决方案来插入一个记录,如果它不存在所以我在这里搜索并找到了解决方案,但我有另一个问题

INSERT INTO closed_answers (question_id, subject_id)
SELECT * FROM (SELECT 2, 2) AS tmp
WHERE NOT EXISTS (
    SELECT question_id FROM closed_answers WHERE question_id = 2 AND subject_id = 2
) LIMIT 1

输出是

#1060 - Duplicate column name '2'

如果我使用任何不相同的2个数字它将起作用,但当2个数字相同时出现问题

Answer 1

使SQL工作的最小变化是为select语句添加别名:

INSERT INTO closed_answers (question_id, subject_id)
SELECT * FROM (SELECT 2 AS question_id, 2 AS subject_id) AS tmp
WHERE NOT EXISTS (
    SELECT question_id
    FROM closed_answers
    WHERE question_id = 2 AND subject_id = 2
) LIMIT 1

但是,如果你有一个独特的约束,(question_id, subject_id)那么你可以使用INSERT IGNORE:

INSERT IGNORE INTO closed_answers (question_id, subject_id)
VALUES (2, 2)