Codeigniter MySQL列where子句中的未知列

Question

I have declared the variable upload_source in SELECT but get error

Unknown column 'upload_source' in 'where clause'

   SELECT b.name as name, filename, upload_date, IF(filename LIKE '%.png%', 1, 0) as type, IF(ex_link!='', 0, 1) as upload_source, title, a.id
    FROM (`all_media` a)
    LEFT JOIN `admins` b ON `b`.`id`=`user_id`
    WHERE `a`.`approved` =  0
    AND `upload_source` =  0
    ORDER BY `filename` DESC

How do i solve?

Answer 1

You cannot use aliased expression/column in where clause. Use the same expression (which you defined in the Select clause), in the Where clause.

From MySQL Documentation :

An alias can be used in a query select list to give a column a different name. You can use the alias in GROUP BY, ORDER BY, or HAVING clauses to refer to the column.

Standard SQL disallows references to column aliases in a WHERE clause. This restriction is imposed because when the WHERE clause is evaluated, the column value may not yet have been determined.

Do the following instead (I have improvised the upload_source = 0 to ex_link != '' ):

 SELECT b.name as name, 
        filename, 
        upload_date, 
        IF(filename LIKE '%.png%', 1, 0) as type, 
        IF(ex_link!='', 0, 1) as upload_source, 
        title, 
        a.id
 FROM `all_media` AS a 
 LEFT JOIN `admins` b ON `b`.`id`=`user_id`
 WHERE `a`.`approved` =  0
   AND ex_link != '' 
 ORDER BY `filename` DESC

Answer 2

In SQL the WHERE keyword could not be used with aggregate functions . Try this with Having Clause :

SELECT b.name as name, filename, upload_date, IF(filename LIKE '%.png%', 1, 0) as type, IF(ex_link!='', 0, 1) as upload_source,title, a.id FROM ( all_media a) LEFT JOIN admins b ON b . id = user_id WHERE a . approved = 0 HAVING upload_source = 0 ORDER BY filename DESC