SQL - not null or condition

Question

I'm quite new to SQL and am facing the following problem. Consider we have a table with two columns:

A         B
10        20
NULL      15
25        10
50        30
NULL      100

What I need is to select rows which satisfy the following conditions:

either
1) A is NULL
or
2) A < B

Which means, as a result I want to see such table:

A         B
10        20
NULL      15
NULL      100

I tried to use the following query:

SELECT * FROM mytable
WHERE A < B OR A is NULL

But it seems like it doesn't work the way I supposed it to.

How should a correct query look like? Thank you!

Answer 1

What I queried was: "SELECT * FROM table WHERE ...some conditions on other columns... AND A IS NULL OR A < B"

You should put the OR comparison in parenthesis:

...AND (A IS NULL OR A < B)