Question

我有3个表，名称分别为city，state和project

城市

id_city |  name_city         
   1    |   JED
   2    |   RYD
   3    |   DMM

状态

带有city.city_id的列city_id外键

 id_state | name_state | city_id
     1    |    JED 1   | 1(JED)
     2    |    RYD 1   | 2(RYD)
     3    |    RYD 2   | 2(RYD)

项目

状态为.city_id的列state_from_city_id_table_state外键

id_project | city_id | state_from_city_id_table_state
      1    |     1   |  1(JED)>> (JED1)     question here 
      2    |     2   |  2(RYD)>> (RYD 1 or2) question here

现在我选择的问题是city_id from project table ...像1一样，我只想在city_id from state table number 1 without number 2中看到state_id from table project

像JED > JED1 only i don't wanna see RYD1 and RYD2

Answer 1

SELECT ct.*, st.*, pr.* FROM `city` ct LEFT JOIN `state` st ON ct.`id_city` = st.`state_id` LEFT JOIN `project` pr ON ct.`id_city` = pr.`city_id`

在3个表之间选择条件

1 个答案: