No of columns in a table and SQL performance

How does the table size effects sql performance?
I am comparing 2 tables , with same number of rows(54 million rows) ,
table1(columns a,b,c,d,e,f..) has 40 columns
table2 (columns (a,b,c,d)
SQL uses columns a,b.
SQL using table2 runs in 1 sec.
SQL using table1 runs in 30 min.
Can any one please let me know how the table size , number of columns in table efects the performance of SQL's?
Thanks
jeevan.

user600431 wrote:
This is a general question. I just want to compare table with more columns and table with less columns with same number of rows .
I am finding that table with less columns is good in performance , than the table with more columns.
Assuming there are no row chains , will there be any difference in performance with the number of columns in a table.Jeevan,
the question is not how many columns your table has, but how large your table segment is. If your query runs a full table scan it has to read through the whole table segment, so in that case the size of the table matters.
A table having more columns potentially has a larger row size than a table with less columns but this is not a general rule. Think of large columns, e.g. varchar2 columns, think of blank (NULL) columns and you can easily end up with a table consisting of a single column taking up more space per row than a table with 200 columns consisting only of varchar2(1) columns.
Check the DBA/ALL/USER_SEGMENTS view to determine the size of your two table segments. If you gather statistics on the tables then the dictionary will contain information about the average row size.
If your query is using indexes then the size of the table won't affect the query performance significantly in many cases.
Regards,
Randolf
Oracle related stuff blog:
http://oracle-randolf.blogspot.com/
SQLTools++ for Oracle (Open source Oracle GUI for Windows):
http://www.sqltools-plusplus.org:7676/
http://sourceforge.net/projects/sqlt-pp/

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