topic Re: Performance LOAD; SQL SELECT in QlikView

Performance LOAD; SQL SELECT

Fri, 06 Feb 2015 11:21:13 GMT

Hello everyone,

Is there a difference in terms of performance in doing :

LOAD

SQL SELECT *

FROM ..

LOAD

SQL SELECT A,B

FROM...

Let's say the table has a lot of fields.

Thank you.

Have a good day.

Laura

Re: Performance LOAD; SQL SELECT

jerrysvensson — Fri, 06 Feb 2015 11:35:21 GMT

Yes there could be a huge difference if your table has like 100 fields.

Re: Performance LOAD; SQL SELECT

datanibbler — Fri, 06 Feb 2015 11:36:09 GMT

Hi Laura,

I'd say the performance should logically be bettter if, out of a lot of fields in the database_table, you SELECT only the fields that you need. The difference is probably not too much, though, as the preceding LOAD takes only those two fields ...

Re: Performance LOAD; SQL SELECT

giakoum — Fri, 06 Feb 2015 11:36:38 GMT

especially if large text fields are included

Re: Performance LOAD; SQL SELECT

jerrysvensson — Fri, 06 Feb 2015 11:42:59 GMT

I have seen data loads go from one hour (Select *) to five minutes (Select A,B). We had a table with 170 fields.

Re: Performance LOAD; SQL SELECT

Anonymous — Fri, 06 Feb 2015 12:02:45 GMT

Hi,

There will be huge difference between Getting two fields and 100's of fields from database in terms of performance.

As SQL SELECT statement does Implicit LOAD.

Regards

Neetha

Re: Performance LOAD; SQL SELECT

Anonymous — Fri, 06 Feb 2015 12:30:32 GMT

additionally to existing answers there is another aspect

Select * requires a full table scan which takes time

select a,b might take use of an index which is much faster

in our case we dropped the load time from 1hour to 5 minutes (select * got 6 fields, later we used select with 2 fields)!