SQL查询; 求和字段

Question

I'm stuck on a sum in sql. What I'm trying to do is the following:

I have a table which stores id's of items. Those id's are linked to another table 'library' with the description, the names and the points of those items.

Now I need to grab some different items in the library and calculate the total of those points together.

I hope I was clear enough. Beneath the query I'm using:

"SELECT SUM(`points`) AS `total` FROM `library` WHERE `id` = '".    $row2['lid'] ."'"

Answer 1

a possible way to do it is:

"SELECT SUM(`points`) AS `total` FROM `library` WHERE `id` in (". $IDlist .")"

Where $IDList is a comma separated list of your IDs, like for example "'1', '2', '3'" .

If these are numeric IDs you can avoid the single quote marks, they are used for strings.

Answer 2

If the ids are coming from a table, then you should use join , in , or exists . Something like:

select sum(points) as total
from library l join
     otheridtable oit
     on l.id = oit.id;

You should not move the ids from the database to the application layer, just to stuff them into a string and send them back to the database. That is inelegant, inefficient, and more work than necessary.