How can i improve this query.

Question

Hi guys i am beginner , just wanted to know some info , how can i improve this query ..
select *
from tableA A, viewB B,
where A.key = B.key
and a.criteria1 = '111'
and a.criteria2 = some_funtion(a.key)
one more thing should function should be on left side of equal sign.
will a join make it better or something else is needed more than that .

Answer 1

952936 wrote:
Hi guys i am beginner , just wanted to know some info , how can i improve this query ..
select *
from tableA A, viewB B,
where A.key = B.key
and a.criteria1 = '111'
and a.criteria2 = some_funtion(a.key)
one more thing should function should be on left side of equal sign.
will a join make it better or something else is needed more than that .If you are a beginner try to learn the ANSI Syntax. This will help you a lot to write better queries.
Your select would look like this in ANSI.
select *
from tableA A
JOIN viewB B ON A.key = B.key
WHERE a.criteria1 = '111'
and a.criteria2 = some_function(a.key);The good thing here is that this separates the typical joining part of the select from the typical filter criteria.
The other syntax very often let you forget one join. Just because there are so many tables and so many filters, that you just don't notice correctly anymore what was join and what not.
If you notice that the number of column is not what you expect, you can easiely modify the query and compare the results.
example A
Remove View B from the query (temporarily comment it out).
select *
from tableA A
--JOIN viewB B ON A.key = B.key
WHERE a.criteria1 = '111'
and a.criteria2 = some_funtion(a.key)
example B
You notice, that values from A are missing. Maybe because there is no matching key in ViewB? Then change the join to an outer join.
select *
from tableA A
LEFT OUTER JOIN viewB B ON A.key = B.key
WHERE a.criteria1 = '111'
and a.criteria2 = some_funtion(a.key)(The outer keyword is optional, left join would be enough).