The Value Of CROSS APPLY

Kendra Little talks about one of my favorite T-SQL operators:

Here’s my top 3 favorite uses for CROSS APPLY and OUTER APPLY:

  1. APPLY is fantastic for calling table valued functions. I didn’t include questions about those in the quiz, simply for the purposes of keeping the code simple, and because I wanted the quiz to be about thinking through how apply works — but it’s still the #1 use.

  2. Another thing I might use it for is when a query needs a correlated subquery — somewhat like an inline function.

  3. And I also like it for queries that have a calculation that needs to be done and which is referenced in multiple columns in the query, or perhaps also in a predicate and the select. You can perform the computation once in the apply and then reference it multiple times. That way if you have to change the formula later on, you only have to change it in once place, plus I find it’s easier to read in some cases.

Item number three is something I learned from an older blog post Kendra wrote and regularly use APPLY for this purpose.

Related Posts

Using Calendar Tables

I have a post up on using calendar tables: There’s one problem with picking a SQL Saturday in April: Easter and Passover tend to run right around that time, and nobody wants a SQL Saturday on Passover or the day before Easter. Unfortunately, our calendar table doesn’t include holiday information. So let’s add it! Working […]

Read More

Finding The Last Non-Null Value With Snowflake

Koen Verbeeck shows how two words makes solving a problem with Snowflake a lot easier than with SQL Server: Sometimes you need to find the previous value in a column. Easy enough, the LAG window function makes this a breeze (available since SQL Server 2012). But what if the previous value cannot be null? You […]

Read More

Categories

July 2018
MTWTFSS
« Jun Aug »
 1
2345678
9101112131415
16171819202122
23242526272829
3031