视图查询

视图查询可以实现不依赖数据库视图的多表查询，并不需要数据库支持视图，例如：

Db::view('User','id,name')
    ->view('Profile','truename,phone,email','Profile.user_id=User.id')
    ->view('Score','score','Score.user_id=Profile.id')
    ->where('score','>',80)
    ->select();

生成的sql语句类似于：

SELECT User.id,User.name,Profile.truename,Profile.phone,Profile.email,Score.score FROM think_user User INNER JOIN think_profile Profile ON Profile.user_id=User.id INNER JOIN think_socre Score ON Score.user_id=Profile.id WHERE Score.score > 80

注意，视图查询无需调用table和join方法，并且在调用where和order方法的时候只需要使用字段名而不需要加表名。

默认使用INNER join查询，如果需要更改，可以使用：

Db::view('User','id,name')
    ->view('Profile','truename,phone,email','Profile.user_id=User.id','LEFT')
    ->view('Score','score','Score.user_id=Profile.id','RIGHT')
    ->where('score','>',80)
    ->select();

生成的SQL语句类似于：

SELECT User.id,User.name,Profile.truename,Profile.phone,Profile.email,Score.score FROM think_user User LEFT JOIN think_profile Profile ON Profile.user_id=User.id RIGHT JOIN think_socre Score ON Score.user_id=Profile.id WHERE Score.score > 80

可以使用别名：

Db::view('User',['id'=>'uid','name'=>'account'])
    ->view('Profile','truename,phone,email','Profile.user_id=User.id')
    ->view('Score','score','Score.user_id=Profile.id')
    ->where('score','>',80)
    ->select();

生成的SQL语句变成：

SELECT User.id AS uid,User.name AS account,Profile.truename,Profile.phone,Profile.email,Score.score FROM think_user User INNER JOIN think_profile Profile ON Profile.user_id=User.id INNER JOIN think_socre Score ON Score.user_id=Profile.id WHERE Score.score > 80

可以使用数组的方式定义表名以及别名，例如：

Db::view(['think_user'=>'member'],['id'=>'uid','name'=>'account'])
    ->view('Profile','truename,phone,email','Profile.user_id=member.id')
    ->view('Score','score','Score.user_id=Profile.id')
    ->where('score','>',80)
    ->select();

生成的SQL语句变成：

SELECT member.id AS uid,member.name AS account,Profile.truename,Profile.phone,Profile.email,Score.score FROM think_user member INNER JOIN think_profile Profile ON Profile.user_id=member.id INNER JOIN think_socre Score ON Score.user_id=Profile.id WHERE Score.score > 80