Bizarre SQL Union/All Result

[Eluros]

Greetings,

So, for work, I have two queries, A and B. When run by itself, A returns 1 row (with 1 varchar column) and B returns 1984 rows (with 1 varchar column). Neither A nor B, by themselves, return any null results.

However, when I run the following:

A
UNION ALL
B

17 of the resulting 1985 rows are null. Union returns 1963 (of the expected 1985) rows, 22 of which are presumably consolidated into the single "null" that shouldn't exist.

I find it bizarre that Union and Union All return null rows when the queries that compose them don't return any null rows. Further, I find it odd that the number of null rows varies!

Any ideas what can cause this, oh ye SQL gods?

As always, much obliged for your help.

 

[Albatross]

Could you post your queries?Do they include functions by any chance?

 

[Eluros]

Could you post your queries?Do they include functions by any chance?

I'm at home now-- I actually posted near the end of the day-- but I'll have a sanitized version tomorrow, hopefully. Thanks.

 

[Eluros]

So, I was able to figure out the core problem: I was concatenating a series of values, one of which could have potentially been null. As I should have prepared for, value + null == null.

I added a coalesce to replace any null values with empty strings and everything works as it should. Should have thought of that from the get-go.