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Database Forum / DB2 Topics / September 2008

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query plan question

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uwcssa@gmail.com - 25 Sep 2008 19:29 GMT
I am running dpf on v95.

when checking my query plans, sometimes there is a "^" symbol before
the operators,
for example   Hashjoin becomes "^Hashjoin".  I am wondering if this ^
has some meaning.

also, is there a way to hint the optimizer about the selectivity of a
non-UDF?
Seems to me only the following is allowed:

      select * from syscat.tables where   myfunc(tabschema)='xxx'
selectivity  0.1

but it would be useful to do the following  (i always get errors on
this)

      select * from syscat.tables where   tabschema='xxx'
selectivity  0.1

Is there any trick to enable the above in db2?

thanks
Ian - 26 Sep 2008 18:27 GMT
> I am running dpf on v95.
>
> when checking my query plans, sometimes there is a "^" symbol before
> the operators,
> for example   Hashjoin becomes "^Hashjoin".  I am wondering if this ^
> has some meaning.

What tool is generating this?  db2exfmt shows operators in upper case.
Can you show the output?

> also, is there a way to hint the optimizer about the selectivity of a
> non-UDF?
[quoted text clipped - 8 lines]
>        select * from syscat.tables where   tabschema='xxx'
> selectivity  0.1

Did you enable the DB2_SELECTIVITY registry variable?
 
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