請假需要層層審批,每次審覈存儲當前審批人id,需要關聯查出對應的名稱
方式一:(複雜且性能不佳)
ELECT
absence.id,
(
SELECT
name
FROM
users
WHERE
absence.first_user_id= users.id
) AS firstName,
(
SELECT
name
FROM
users
WHERE
absence.second_user_id= users.id
) AS secondName
FROM
absence
方式二:(關聯多次,每次關聯一個字段)
SELECT
n.id,
m.name,
q.name
FROM
absence
LEFT JOIN users m ON n.first_user_id= m.id
LEFT JOIN users q ON n.second_user_id = q.id