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