> Well, for starters, see if PostgreSQL is currently using any indexes via
> EXPLAIN. First rule of performance tuning: don't.
I'm designing a new application. Data is not available yet.
I'm using Postgres 8.1 in Windows. Database encoding is UTF-8
lc_ctype is Estonian_Estonia.1257.
lc_collate is Estonian currently. However I can set lc_collate to C if this
solves this issue.
Doc says that
" to allow PostgreSQL to use indexes with LIKE clauses under a non-C locale,
several custom operator classes exist"
I don't understand "non-C locale". Does this mean lc_collate or also some
other lc_ setting ?
> If it's not (which is probably the case), then your best bet is to
> create functional indexes; ie:
>
> CREATE INDEX mytable__col1_4 ON mytable( substring( col1 for 4 ) );
>
> You can then either
>
> SELECT ... WHERE substring( col1 for 4 ) = blah
I need to optimize queries with variable number of characters in beginning
like
SELECT ... WHERE substring( col1 for 1 ) = 'f'
SELECT ... WHERE substring( col1 for 2 ) = 'fo'
SELECT ... WHERE substring( col1 for 3 ) = 'foo'
etc
This approach requires creating 10 indexes for each column which is
unreasonable.
In my current dbms, Microsoft Visual FoxPro I have a single index
CREATE INDEX i1 ON mytable(col1)
I can use queries:
WHERE col1 BETWEEN 'f' and 'f'+CHR(255)
WHERE col1 BETWEEN 'fo' and 'fo'+CHR(255)
WHERE col1 BETWEEN 'foo' and 'foo'+CHR(255)
All those queries can use same index automatically in all locales. CHR(255)
is last character in any lc_collate sequence. CHR(255) is not used in col1
data.
How to get same functionality in Postgres ?
Does there exist unicode special character which is greater than all other
chars ?
Andrus.
