Does the number of WHERE statements affects query performance?

Question

I have a table with millions of rows. I need to find one document (WHERE DocumentName = 'xxx'). Table is being populated since last century. Will the query be faster if I include (AND Date > '2021-01-01') in a WHERE statement? Because I need only recent one records.

Answer 1

It should be faster, but there are many considerations.

The simplest is that returning less data is generally faster. The additional where conditions (which you describe as being connected by AND) might allow more optimizations as well -- particularly indexes or partitions, for instance.

That said, there is some overhead for the additional data check, which adds a little bit of overhead (but typically much, much less than returning more data). And more complicated where clauses can confuse the optimizer.

But most importantly: If you only need more recent records, you should write the query that returns what you really need.