sql server - Performance of COUNT SQL function

Question

I have two choices when writing an SQL statement with the COUNT function.

1. SELECT COUNT(*) FROM <table_name>
2. SELECT COUNT(some_column_name) FROM <table_name>

In terms of performance, what is the best SQL statement? Can I obtain some performance gain by using option 1?

Answer 1

Performance should not matter because they do 2 different aggregates

• COUNT(*) is all rows, including NULLs
• COUNT(some_column_name), excludes NULL in "some_column_name"

See the "Count(*) vs Count(1)" question for more