diff options
| author | Tom Lane | 2000-04-16 04:41:03 +0000 |
|---|---|---|
| committer | Tom Lane | 2000-04-16 04:41:03 +0000 |
| commit | 82849df6c637c09fe484ed11e1035c158f128e81 (patch) | |
| tree | ddb8f0f3af666ad331ae05498bd039d2e65e783f /doc/src/sgml | |
| parent | 8c3b52e7b2d90a35be1370a10fcf02218fa4ae99 (diff) | |
Add new selectivity estimation functions for pattern-matching operators
(LIKE and regexp matches). These are not yet referenced in pg_operator,
so by default the system will continue to use eqsel/neqsel.
Also, tweak convert_to_scalar() logic so that common prefixes of strings
are stripped off, allowing better accuracy when all strings in a table
share a common prefix.
Diffstat (limited to 'doc/src/sgml')
| -rw-r--r-- | doc/src/sgml/xoper.sgml | 8 |
1 files changed, 4 insertions, 4 deletions
diff --git a/doc/src/sgml/xoper.sgml b/doc/src/sgml/xoper.sgml index a0513a7051d..2c938148fcd 100644 --- a/doc/src/sgml/xoper.sgml +++ b/doc/src/sgml/xoper.sgml @@ -1,5 +1,5 @@ <!-- -$Header: /cvsroot/pgsql/doc/src/sgml/xoper.sgml,v 1.9 2000/03/31 03:27:41 thomas Exp $ +$Header: /cvsroot/pgsql/doc/src/sgml/xoper.sgml,v 1.10 2000/04/16 04:41:01 tgl Exp $ --> <Chapter Id="xoper"> @@ -254,9 +254,9 @@ SELECT (a + b) AS c FROM test_complex; <para> You can frequently get away with using either eqsel or neqsel for operators that have very high or very low selectivity, even if they - aren't really equality or inequality. For example, the regular expression - matching operators (~, ~*, etc) use eqsel on the assumption that they'll - usually only match a small fraction of the entries in a table. + aren't really equality or inequality. For example, the + approximate-equality geometric operators use eqsel on the assumption that + they'll usually only match a small fraction of the entries in a table. </para> <para> |