There is nothing specific about
SELECT here. There is no semantic difference between
The issue being described is that if you issue these three semantically identical statements:
SELECT thing FROM mytable;
select thing from mytable;
Select Thing From MyTable;
the database treats them as three entirely different entities, that will each occupy some space in the library cache. They will each have been parsed individually, costing CPU each time, even if the resulting execution plan are are identical.
Same thing if you have two identical queries but one with a comment and another without - they will be treated as different statements entirely by the engine, and each consume resources. (I believe even spacing matters.)
(This is actually helpful for debugging. If you're trying different settings to optimize a query without changing the query text, add a comment describing the current settings each time you run it. You're guaranteed a re-parse, and can find the individual runs in
[g]v$sql easily with those comments. This wouldn't work if the engine "normalized" the query text before parsing.)
What this means for you is that you should be consistent with your query syntax. Choose a "coding" style and stick with it to avoid littering the various caches with semantically identical queries.
Example: notice the three different SQL IDs.
select a from foo;
Select a From foo;
SELECT a FROM foo;
select * from v$sql where sql_text like '%foo%';
dxdhrwqjpn6b7 Select a From foo
0dqb3y3bask98 select a from foo
1y13x9j2rwzuz SELECT a FROM foo