where子句中的列“ u_id”不明确

Question

SELECT  `attendence`.`u_id` ,
        DATE_FORMAT(date,'%d-%m-%Y') as  `date`,
        `attendence`.`checkin`, 
        `attendence`.`checkout`,
         `users`.`firstname`,
         `users` .`lastname`
 FROM  `attendence`
 INNER JOIN  `users` ON  `attendence`.`u_id` = `users`.`u_id`
 WHERE  DATE_FORMAT( DATE,  '%Y-%m' ) =  '$combined' AND `u_id`='$u_id';

please help guys

when i removed AND u_id ='#u_id it works but returns all employee details'

Answer 1

you need to specify what table should the column u_id came from since both tables has this column.

AND `attendence`.`u_id`='$u_id';

OR

AND `users`.`u_id`='$u_id';

choose one that satifies your needs. Anyway, either of the two functions the same since they are the linking columns of both tables.

Answer 2

replace

`u_id`='$u_id';

by

`users`.`u_id`='$u_id';

Answer 3

If you have u_id in multiple tables that you are using in your query then you need to specify which u_id you want to use.

use this in your where clause:

`attendence`.`u_id` = '$u_id';