index and ilke question
Hi,
I want to use the following query:
select * from customers where lastname ilike 'jansen%'
Explain says it uses a sequential scan on customers while there is an
index on lastname (and 'jansen%' contains 1800 entries in a table of
370.000 customers so a index scan should be more logical?).
The docs say "However, if your server does not use the C locale you will
need to create the index with a special operator class to support
indexing of pattern-matching queries."
This seems to be the case as it does not use the index.
Two questions:
1. How can I check if my (PostgreSQL or Linux?) server uses the C
locale ?
2. And if it does not the (correct?) C locale is the syntax for a
correct index the following, assuming that lastname is of type "text":
CREATE INDEX test_index ON prototype.customers (lastname
text_pattern_ops);
(I tried this, but it did not change anything so I assume that either my
assumptions about when to use an index as described above or my syntax
are wrong)
TIA
--
Groeten,
Joost Kraaijeveld
Askesis B.V.
Molukkenstraat 14
6524NB Nijmegen
tel: 024-3888063 / 06-51855277
fax: 024-3608416
e-mail: J.Kraaijeveld@Askesis.nl
web: www.askesis.nl
SHOW ALL list all show the value of a run-time parameter.
LC_COLLATE String sort order
LC_CTYPE Character classification (What is a letter? Its upper-case
equivalent?)
LC_MESSAGES Language of messages
LC_MONETARY Formatting of currency amounts
LC_NUMERIC Formatting of numbers
LC_TIME Formatting of dates and times
LC_COLLATE and LC_CTYPE is set on C, you just need index on the text field.
If not C then you can create an index with a special operator class (s.
documation 11.6).
----- Original Message -----
From: "Joost Kraaijeveld" <J.Kraaijeveld@Askesis.nl>
To: "Pgsql-General" <pgsql-general@postgresql.org>
Sent: Sunday, September 11, 2005 10:49 AM
Subject: [GENERAL] index and ilke question
Show quoted text
Hi,
I want to use the following query:
select * from customers where lastname ilike 'jansen%'
Explain says it uses a sequential scan on customers while there is an
index on lastname (and 'jansen%' contains 1800 entries in a table of
370.000 customers so a index scan should be more logical?).The docs say "However, if your server does not use the C locale you will
need to create the index with a special operator class to support
indexing of pattern-matching queries."This seems to be the case as it does not use the index.
Two questions:
1. How can I check if my (PostgreSQL or Linux?) server uses the C
locale ?2. And if it does not the (correct?) C locale is the syntax for a
correct index the following, assuming that lastname is of type "text":CREATE INDEX test_index ON prototype.customers (lastname
text_pattern_ops);(I tried this, but it did not change anything so I assume that either my
assumptions about when to use an index as described above or my syntax
are wrong)TIA
--
Groeten,Joost Kraaijeveld
Askesis B.V.
Molukkenstraat 14
6524NB Nijmegen
tel: 024-3888063 / 06-51855277
fax: 024-3608416
e-mail: J.Kraaijeveld@Askesis.nl
web: www.askesis.nl---------------------------(end of broadcast)---------------------------
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