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sql内联语法基础语法(inner join) SELECT * FROM 表1 inner join 表2 on 表1.userid=表2.userid sql内联语法说明:上面的语句就是查询表1和表2两个表,只要两个表中的userid字段相同的话就拼成一行显示出来。 45it.com注:以上语法同等select * from 表1,表2

   sql内联语法基础语法(inner join)

  SELECT * FROM 表1 inner join 表2 on 表1.userid=表2.userid

  sql内联语法说明:上面的语句就是查询表1和表2两个表,只要两个表中的userid字段相同的话就拼成一行显示出来。

  45it.com注:以上语法同等select * from 表1,表2 where 表1.userid=表2.userid,而使用sql内联的话,将会提高很多效率。

  sql左联语法基础语法(left outer join)

  SELECT * FROM 表1 LEFT OUTER JOIN 表2 ON 表1.userid=表2.userid

  sql左联语法说明:显示表1中所有的行,,并且把表2中所有符合条件的数据都显示到结果集中,如果表2中不符合的数据的都不会显示在结果集中,并且以null显示。

  sql右联语法基础语法(right outer join)

  SELECT * FROM 表1 RIGHT OUTER JOIN 表2 ON 表1.userid=表2.userid

  sql左联语法说明:显示表2中所有的行,并且把表1中所有符合条件的数据都显示到结果集中,如果左表1中不符合的数据的都不会显示在结果集中,并且以null显示。

  sql全联语法基础语法(full outer join)

  SELECT * FROM 表1 FULL OUTER JOIN 表2 ON 表1.userid=表2.userid

  sql左联语法说明:以上sql全联意思就是显示表1和表2所有行,简单的说吧,就是把表1和表2所有行都组合起来,之后再过滤掉重复的数据并显示到结果集中。

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