concatenation of null values in SQL from a join of tables

Today we were trying to join 2 fields from different tables with a left outer join. This means that if there is nothing in the joining table the rows are returned as null. By default SQL wont give you a result in the joining request. Lets have an example. You want to get categories and […]

Today we were trying to join 2 fields from different tables with a left outer join. This means that if there is nothing in the joining table the rows are returned as null. By default SQL wont give you a result in the joining request. Lets have an example. You want to get categories and their parents one level deep.

This would only render the rows that have a child category – i.e. where the CategoryParentID is not null. To solve this issue and get the categories at the top level as well, we need to tell SQL to resolve nulls in a concatenation, rather than ignore them:

This sql variable tells the process to allow nulls on one side of the join.

Duncan Isaksen-Loxton

Educated as a web developer, with over 20 years of internet based work and experience, Duncan is a Google Workspace Certified Collaboration Engineer and a WordPress expert.

1 Comment

Comments are closed.

Login
Log in below to access your courses.
Log In With Google
Forgot Password
Enter your email address or username and we’ll send you instructions to reset your password.