Overview of pattern matching operators
~~) is simple and fast but limited in its capabilities.
~~*) the case insensitive variant.
pg_trgm extends index support for both.
~ (regular expression match) is powerful but more complex and may be slow for anything more than basic expressions.
~* is the case insensitive variant.
SIMILAR TO is just pointless. A peculiar halfbreed of
LIKE and regular expressions. I never use it. See below.
% is the "similarity" operator, provided by the additional module
pg_trgm. See below.
@@ is the text search operator. See below.
Basics about pattern matching in the manual.
... is pretty much the optimum. Syntax won't get much shorter, query won't get much faster:
WHERE name LIKE 'B%' OR name LIKE 'D%'
ORDER BY 1;
If you really want to shorten the syntax, use a regular expression with branches:
WHERE name ~ '^(B|D).*'
Or slightly faster, with a character class:
WHERE name ~ '^[BD].*'
A quick test without index yields faster results than for
SIMILAR TO in either case for me.
With an appropriate B-Tree index in place,
LIKE wins this race by orders of magnitude.
Index for superior performance
If you are concerned with performance, create an index like this for bigger tables to support left-anchored search patterns (matching from the start of the string):
CREATE INDEX spelers_name_special_idx ON spelers (name COLLATE "C");
Requires per-column collation support added with Postgres 9.1.
In DBs running with the "C" locale (not typical), a plain B-tree index does the job.
In older versions (or still today if you insist), you can use the special operator class
text_pattern_ops for the same purpose:
CREATE INDEX spelers_name_special_idx ON spelers (name text_pattern_ops);
SIMILAR TO or regular expressions with basic left-anchored expressions can use this index, too. But not with branches
(B|D) or character classes
[BD] (at least in my tests on PostgreSQL 9.0).
Trigram matches or text search use special GIN or GiST indexes.
Beginning with Postgres 9.1 you can install the additional module
pg_trgm to provide index support for any
ILIKE pattern (and simple regexp patterns with
~*) using a GIN or GiST index.
Details, example and links:
pg_trgm also provides these operators:
% - the "similarity" operator
%>) - the "word_similarity" operator in Postgres 9.6 or later
%>>) - the "strict_word_similarity" operator in Postgres 11 or later
Is a special type of pattern matching with separate infrastructure and index types. It uses dictionaries and stemming and is a great tool to find words in documents, especially for natural languages.
Prefix matching is also supported:
As well as phrase search since Postgres 9.6:
Consider the introduction in the manual and the overview of operators and functions.
Additional tools for fuzzy string matching
The additional module fuzzystrmatch offers some more options, but performance is generally inferior to all of the above.
In particular, various implementations of the
levenshtein() function may be instrumental.
Why are regular expressions (
~) always faster than
The answer is simple.
SIMILAR TO expressions are rewritten into regular expressions internally. So, for every
SIMILAR TO expression, there is at least one faster regular expression (that saves the overhead of rewriting the expression). There is no performance gain in using
SIMILAR TO ever.
And simple expressions that can be done with
~~) are faster with
SIMILAR TO is only supported in PostgreSQL because it ended up in early drafts of the SQL standard. They still haven't gotten rid of it. But there are plans to remove it and include regexp matches instead - or so I heard.
EXPLAIN ANALYZE reveals it. Just try with any table yourself!
EXPLAIN ANALYZE SELECT * FROM spelers WHERE name SIMILAR TO 'B%';
Seq Scan on spelers (cost= ...
Filter: (name ~ '^(?:B.*)$'::text)
SIMILAR TO has been rewritten with a regular expression (
Ultimate performance for this particular case
EXPLAIN ANALYZE reveals more. Try, with the afore-mentioned index in place:
EXPLAIN ANALYZE SELECT * FROM spelers WHERE name ~ '^B.*;
-> Bitmap Heap Scan on spelers (cost= ...
Filter: (name ~ '^B.*'::text)
-> Bitmap Index Scan on spelers_name_text_pattern_ops_idx (cost= ...
Index Cond: ((prod ~>=~ 'B'::text) AND (prod ~<~ 'C'::text))
Internally, with an index that is not locale-aware (
text_pattern_ops or using locale
C) simple left-anchored expressions are rewritten with these text pattern operators:
~<~. This is the case for
SIMILAR TO alike.
The same is true for indexes on
varchar types with
So, applied to the original question, this is the fastest possible way:
WHERE name ~>=~ 'B' AND name ~<~ 'C'
OR name ~>=~ 'D' AND name ~<~ 'E'
ORDER BY 1;
Of course, if you should happen to search for adjacent initials, you can simplify further:
WHERE name ~>=~ 'B' AND name ~<~ 'D' -- strings starting with B or C
The gain over plain use of
~~ is tiny. If performance isn't your paramount requirement, you should just stick with the standard operators - arriving at what you already have in the question.