的Node.js：如何使用一个查询的输出到另一个查询

Question

我是新来的node.js的投入，我想查询到另一个查询的输入输出，请帮助

pool.getConnection(function(err, connection) { 
    connection.query("select * from tbl_chat", function(err, rows) { 
     console.log(rows[0]['from_id']); 
     var fromid = rows[0]['from_id']; 
    }); 
    console.log(fromid);//throws ReferenceError: fromid is not defined 
    console.log(rows[0]['from_id']);// throws ReferenceError: rows is not defined 

    //I want to use the fromid in the following query 

    /*connection.query("select * from tbl_chat where from_id=?",[fromid], function(err, rows) { 
     console.log(rows[0]['from_id']); 
    });*/ 
}); 

Answer 1

的NodeJS数据库查询是异步的，所以你必须把你的console.log放在回调中，或者用promise来做。

试试：

pool.getConnection(function(err, connection) { 
    connection.query("select * from tbl_chat", function(err, rows) { 
     console.log(rows[0]['from_id']); 
     var fromid = rows[0]['from_id']; 
     console.log(fromid); 
     console.log(rows[0]['from_id']); 
     connection.query("select * from tbl_chat where from_id=?",[fromid], function(err, rows) { 
      console.log(rows[0]['from_id']); 
     }); 
    }); 
});