数据库加强

数据查询加强篇

一.多表连接

• 内连接

  
  
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• 左外连接

  
  
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• 右外连接
  

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  SELECT *
  FROM
  (
  (
  (
  students st
  JOIN scores sc
  ON st.sno = sc.sno
  )
  JOIN courses co
  ON sc.cno = co.cno
  )
  JOIN teachers te
  ON te.tno = co.tno
  );

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