Question

I’m reading though this db query, and i’m not sure that I need the l. before each selection..

What does l. as in l.id or l.node_id stand for? Do I need it? If not, what would I use it for?

        SELECT
            l.id, l.node_id,
            l.name, l.phone, l.email
        FROM
            leads l
        WHERE
            l.active = 1
            AND agent_id = '.$user->id.'
        GROUP BY l.id

Answer 1

It’s an alias, standing for the table. FROM leads l means “from the table leads, which will be referred to as l elsewhere in this query”. To write the query without an alias, you could write:

SELECT leads.id, leads.node_id,
       leads.name, leads.phone, leads.email
  FROM leads
 WHERE leads.active = 1
   AND agent_id = ...
 GROUP BY leads.id
;

But since there’s only one table in this query, you don’t need to use any prefix at all; something like this is perfectly fine:

SELECT id, node_id,
       name, phone, email
  FROM leads
 WHERE active = 1
   AND agent_id = ...
 GROUP BY id
;

Normally a prefix like this (either leads. or l.) is used when there’s some ambiguity that the query-writer wants to address — either to avoid confusing the database engine, or to avoid confusing a human reading the query, or both — but some people are in the habit of always using these prefixes, both for explicitness and so they never risk introducing an ambiguity.