MySQL中join的7种方法

Posted 2021-03-05 阿凯

join查询的7中方法

• 手写顺序：

  SELECT DISTINCT
  	<select_list>
  FROM
  	<left_table> <join_type>
  JOIN <right_table> ON <join_condition>
  WHERE
  	<where_condition>
  GROUP BY
  	<group_by_list>
  HAVING
  	<having_condition>
  ORDER BY
  	<order_by_condition>
  LIMIT <limit_number>
  

• mysql执行顺序

  FROM <left_table>
  ON <join_condition>
  <join_type> JOIN <right_table>
  WHERE <where_condition>
  GROUP BY <group_by_list>
  HAVING <having_condition>
  DISTINCT <select_list>
  ORDER BY <order_by_condition>
  LIMIT <limit_number>
  

  

• join连接方式：

  • 内连接：

    

 SELECT <select_list> FROM TableA A INNER JOIN TableB B ON A.Key = B.Key

• 左连接：

  

 SELECT <select_list> FROM TableA A LEFT JOIN TableB B ON A.Key = B.Key

• 右连接：

  

 SELECT <select_list> FROM TableA A RIGHT JOIN TableB B ON A.Key = B.Key

• 只有A

  

  SELECT <select_list> FROM TableA A LEFT JOIN TableB B ON A.Key = B.Key WHERE B.Key IS NULL

• 只有B

  

    SELECT <select_list> FROM TableA A RIGHT JOIN TableB B ON A.Key = B.Key WHERE A.Key IS NULL

• 全连接

  

    # MySQL没有FULL OUTER语法。
    SELECT <select_list> FROM TableA A LEFT JOIN TableB B ON A.Key = B.Key
    union
    SELECT <select_list> FROM TableA A RIGHT JOIN TableB B ON A.Key = B.Key;

• A，B各自独有：

  
  ​

  # MySQL没有FULL OUTER语法。
  SELECT <select_list> FROM TableA A LEFT JOIN TableB B ON A.Key = B.Key WHERE B.Key IS NULL
  union
  SELECT <select_list> FROM TableA A RIGHT JOIN TableB B ON A.Key = B.Key WHERE A.Key IS NULL;