Statistics and Indexes

postgresql@bryden.co.za wrote:

Hi

I am from a MSSQL background and am trying to understand something about
statistics in PostgreSQL.

Question 1:
In MSSQL, if you create an index (and you are using MSSQL's default
settings) the Server will automatically create appropriate statistics for
you. Does this happen in PostgreSQL? Or should I explicitly create
statistics for every one of my indexes?

Q2 sort of answers Q1.

Question 2:
I believe ANALYZE keeps indexes and statistics up to date. How often
should this be run (assume that my DB has 200,000 new records daily)?

Try out a VACUUM ANALYZE every hour or three.

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Hi. I am using array_dims to give me dimensions of multidimensional
array ie:

[1:5][1:2]

In my function I want to retreive the value of the second number from
array_dims (5 in example above)

This is what I am trying:

count_str = substr(dimensions from '\[\d\:(\d+)\]\[\d\:\d\]')
(this should give me 5 in the above example)

I have two problems:

1) I can't seem to escape the [ character - so how do I do this?
2) How do I turn my result which is originally text into an integer?

Regards,
David

David Pratt <fairwinds@eastlink.ca> writes:

Hi. I am using array_dims to give me dimensions of multidimensional
array ie:

[1:5][1:2]

In my function I want to retreive the value of the second number from
array_dims (5 in example above)

Why aren't you using array_upper()?

This is what I am trying:
count_str = substr(dimensions from '\[\d\:(\d+)\]\[\d\:\d\]')

Perhaps you forgot to double the backslashes?

regards, tom lane

Hi Tom. I misread the manual. I thought I could not do array_upper on
multidimensional array but it was specific concatenation functions.
Thank you for clarifying this.

Regards,
David

On Tuesday, July 5, 2005, at 01:22 PM, Tom Lane wrote: