Are inner parenthesis needed in the WHERE clause? or anywhere

In the WHERE section or anywhere really where you have multiple conditions like OR’s I know outer parenthesis are required but are the inner ones?

For example my assumption is that

WHERE A.Title='EMP'
AND ( (A.NAME='Mike') OR (A.ID='9001') )

Is the same as writing

WHERE A.Title='EMP'
AND ( A.NAME='Mike' OR A.ID='9001' )

However if we remove the outer parenthesis then I know the query will be different.

Example:

WHERE A.Title='EMP'
AND (A.NAME='Mike') OR (A.ID='9001')

And

WHERE A.Title='EMP'
AND A.NAME='Mike' OR A.ID='9001'

Are both the same thing but not at all what we want.

Is there any chance that data will be evaluated different between the first 2 conditions?

Answer

It’s like in math

2 + 3 * 4   ==> 14

is the same as

2 + (3 * 4)   ==> 14

because the multiplication has a higher precedence than the addition. If you want to do the addition before the multiplication, you must add parenthesis.

(2 + 3) * 4   ==> 20

In SQL AND has a higher precedence than OR. = as comparison operator has a higher precedence than both of them. Therefore the inner parenthesis are not required, because the = will always be performed first. E.g.

A.Title='EMP' AND A.NAME='Mike' OR A.ID='9001'

is the same as

((A.Title='EMP') AND (A.NAME='Mike')) OR (A.ID='9001')

Parenthesis are only required if you want to perform the OR before the AND (even when it appears first in the expression):

A.Title='EMP' AND (A.NAME='Mike' OR A.ID='9001')

Only when operators have the same precedence, they are evaluated left to right.

For the full precedence list, see: Operator Precedence (Transact-SQL)