mysql - 連表操作

mysql有4種表連接關係：

• 內連接：只取兩張表共同的部分(符合條件的部分)

  #語法：左表 inner join 右表 on 判斷條件
  select * from employee inner join employee on employee.id = department.id;
  

• 左連接：在內連接的基礎上保留左表的記錄

  #語法：左表 left join 右表 on 判斷條件
  select * from employee left join employee on employee.id = department.id;
  

• 右連接：在內連接的基礎上保留右表的記錄

  #語法：左表 right join 右表 on 判斷條件
  select * from employee right join employee on employee.id = department.id;
  

• 全連接：在內連接的基礎上保留左右兩表沒有對應關係的記錄

  語法：左連接語法 union 右連接語法；

  select * from employee inner join employee on employee.id = department.id
  union
  select * from employee left join employee on employee.id = department.id;