Checking whether an item does not exist in another table

Question

My tables are set up something like this:

table name: process
fields: name, id_string

table name: value_seach
fields: id_string, value

I w

Answer 1

The query you want should look something like this. Note that a JOIN will be significantly faster than a subquery in the WHERE clause.

SELECT p.name, p.id_string
FROM process p
LEFT OUTER JOIN value_search v
   ON p.id_string = v.id_string
   AND p.id_string IS NOT NULL
   AND v.id_string IS NULL

An equally valid variant of the query above would be:

SELECT p.name, p.id_string
FROM process p
LEFT OUTER JOIN value_search v
   ON p.id_string = v.id_string
WHERE
   p.id_string IS NOT NULL
   AND v.id_string IS NULL