MySQL查询WHERE x和是否设置y

Question

I've been working on a project at work and I need data from two tables. I'm no expert on MySQL queries, but I got this far:

SELECT *
FROM `p_list` AS pl
JOIN `employee` AS em
WHERE em.id =10
AND pl.employee_id =10

It works fine when there is a pl.employee_id, but returns o result where there isn't. It makes sense, but I don't know how i can get it to return where em.id=10 and if pl.employee_id is set.

I'm about to give up and just run two queries and let PHP do the dirty work.

Answer 1

Try this, use LEFT JOIN

SELECT *
FROM   `p_list` AS pl
       LEFT JOIN `employee` AS em
          ON em.id = pl.employee_ID
WHERE  em.id = 10

Basically, what you are doing now is an INNER JOIN . INNER JOIN is different from LEFT JOIN ( which is what you need ). INNER JOIN only returns result if a record specified in the join condition has atleast one match on the other table. LEFT JOIN , on the other hand , returns all rows specified on the LEFT table whether it has a match or none match on the other table.

Answer 2

You can use a left join to do this:

SELECT *
FROM `p_list` AS pl
LEFT JOIN `employee` AS em ON em.id = pl.employee_id
WHERE em.id =10