当任一字段为NULL时，Mysql的字段总和不起作用

Question

Hi i have this code in php to update a balance field in $table5. Now my problem is that when one of the two fields i.e. add or sub is NULL then this does not return balance.

    $fetch_balance = mysql_query("SELECT (SUM (IFNULL(`add`,0))-(SUM (IFNULL(`sub`,0)))          AS `bal` FROM `".$table5."` ");

Please help.

Answer 1

I tried your query, and it worked just fine, after some slight tweak: http://sqlfiddle.com/#!2/a6220/4

The final query should look like this: SELECT (SUM(IFNULL(add,0)))-(SUM(IFNULL(sub,0))) AS bal FROM ".$table5."

You forgot to add a ), and also, you had spaces after SUM(). SUM is a function, and should therefore not have any spaces before the ().