Thanks Dieter. I just got one info that using table aliasing in multi table join can decrease the spool space occupied and hence improving performace. But was not sure sure about this statement. Is it true?
that's definitely false.
There's one specific case where wrong aliases might result in an unwanted cross join (= huge spool):
SELECT table1.col1, -- wrong name, should be t1.col1 instead
FROM table1 AS t1 JOIN table2 AS t2
ON t1.PK = t2.FK;
A table alias replaces the tablename within that query. Using the original tablename doesn't result in an error message (as it does within most other DBMSes), but it causes a CROSS join.