Question

I am trying to do the following but I dont have enough experience with MySQL. Would it be possible for someone to tell me what the query for this will be.

I have a databse with 2 tables

• Brief
• Info

Brief and Info have various fields but I am interested in only ID field.

This is what I am trying to do.

I want to go through all the IDs from
Brief and cross reference them with
all the IDs that exists in Info and
only get the ones that exist in Info
but dont exist in Brief

Thanks

Answer 1

SELECT i.ID
FROM Info i 
  LEFT JOIN Brief b USING(ID)
WHERE b.ID IS NULL

Alternatively:

SELECT i.ID
FROM Info i
WHERE NOT EXISTS (
  SELECT 1
  FROM Brief b
  WHERE b.ID = i.ID
)

See these 2 links for performance comparisons:

• NOT IN vs. NOT EXISTS vs. LEFT JOIN / IS NULL: MySQL
• LEFT JOIN / IS NULL vs. NOT IN vs. NOT EXISTS: nullable columns