In which order does the query's where clause condition is checked

Question

Hi All,
can anyone tell me in which order does oracle evaluate the where clause condition?
for ex: select * from users where user_type='Admin' and stauts='Enabled'

Answer 1

user9981103 wrote:
The conditions in the WHERE clause are checked in the reverse order of the given order.
i.e; first it will check stauts='Enabled'* and then user_type='Admin'* for your given queryWhy do you believe that?
If there is a sufficiently selective b-tree index on USER_TYPE, the optimizer would undoubtedly use that index to process the USER_TYPE = 'Admin' condition and then check the STATUS column.
If there is a sufficiently selective b-tree index on STATUS, the optimizer would undoubtedly use that index to process the STATUS='Enabled' condition and then check the USER_TYPE column.
If there is a composite b-tree index on (STATUS, USER_TYPE), the optimizer would use that index to process the two conditions nearly simultaneously, though technically the leading column of the index is evaluated first. Of course, if you reverse the order of columns in the index, you get a different evaluation order
If there are bitmap indexes on STATUS and USER_TYPE, Oracle can combine the two indexes and evaluate the two conditions simultaneously.
And that is leaving out tons of query plan options and other optimizer wrinkles.
Justin