Simple query to perform joining operation

Question

I am performing MySQL functions using PHP for my webpages.

I have got a table

table name -> users

 uname     oname
  john      alex
  john      murray
  john      joseph
  john      ray

and another table

table name -> more_info

fname    lname         more
 alex     some name   some info
 murray     //           //
 joseph     //           //
 ray       //            //

What I am trying to do is to run a query

Retrieve all the oname column values which are matched with uname john

This statement successfully retrieves the oname column values if uname = john

SELECT oname FROM users WHERE uname = 'john '

Now I want a statement something like this, based on the previously retrieved oname column values

SELECT * FROM more_info WHERE fname=oname // previos ones 

I guess its Join or innerJoin but somehow I am unable to get the correct syntax of it or any other simple query to do this.

My approach

I thought to retrieve the oname column values first and then inside a for loop, based on number of rows returned run a query for each column, but this approach eats up my server.

Answer 1

You can merge your two queries into one by a simple INNER JOIN

SELECT * FROM more_info mi
INNER JOIN users u ON mi.fname = u.oname
WHERE u.uname = 'john'

If there is some chance of null values in more_info table, then you should use LEFT JOIN instead of INNER JOIN . Otherwise it is not necessary.

Answer 2

试试这个查询，

 SELECT * FROM `more_info` `i` INNER JOIN `users` `u` ON `i`.`fname`=`u`.`oname` WHERE `u`.`uname`="john"

Answer 3

我认为以下查询将对您有所帮助。

SELECT * FROM `more_info` WHERE `fname` = (SELECT `oname` FROM `users` WHERE `uname` = "john")

Answer 4

SELECT * FROM users  A
INNER JOIN more_info B
    ON A.oname = B.fname
WHERE uname = 'john'

See the MySQL documentation on the JOIN syntax for details.