创建一个虚拟列以验证其他数据是否存在

Question

mt_user ：

usr_id               usr_login          usr_passwd
  1                   user1               user1
  2                   user2               user2
  3                   user3               user3
  4                   user4               user4

mt_settings ：

sttgs_id                        sttgs_description
   1                                 Setting 1
   2                                 Setting 2
   3                                 Setting 3
   4                                 Setting 4
   5                                 Setting 5

mt_user_settings ：

uss_id               usr_id                   sttgs_id
  1                    1                         1
  2                    1                         2
  3                    2                         5
  4                    3                         2
  5                    3                         3
  6                    3                         5
  7                    4                         4

我需要展示的是这样的数据：

WHERE usr_id='2'：

sttgs_id                   sttgs_description                 has it? (virtual_column)
   1                          Setting 1                              0
   2                          Setting 2                              0
   3                          Setting 3                              0
   4                          Setting 4                              0
   5                          Setting 5                              1

WHERE usr_id='3'：

sttgs_id                   sttgs_description                 has it? (virtual_column)
   1                          Setting 1                              0
   2                          Setting 2                              1
   3                          Setting 3                              1
   4                          Setting 4                              0
   5                          Setting 5                              1

我怎么能正确地做到这一点？

Answer 1

SELECT s.sttgs_id, s.sttgs_description, IF(st.uss_id,1,0) as `has it`
FROM mt_user u
JOIN mt_settings s
LEFT JOIN mt_user_settings us ON us.usr_id = u.usr_id AND us.sttgs_id = s.sttgs_id
WHERE u.usr_id = 2

您也可以在没有用户表的情况下执行此操作

SELECT s.sttgs_id, s.sttgs_description, IF(st.uss_id,1,0) as `has it`
FROM  mt_settings s
LEFT JOIN mt_user_settings us ON us.usr_id = 2 AND us.sttgs_id = s.sttgs_id