PostgreSQL: Case insensitive string comparison
SqlPostgresqlString ComparisonCase InsensitiveSql Problem Overview
Is there a simple ignore-case-comparison for PostgreSQL?
I want to replace:
SELECT id, user_name
FROM users
WHERE lower(email) IN (lower('[email protected]'), lower('[email protected]'));
With something like:
SELECT id, user_name
FROM users
WHERE email IGNORE_CASE_IN ('[email protected]', '[email protected]');
The like and ilike operators work on single values (e.g. like '[email protected]'), but not on sets.
Sql Solutions
Solution 1 - Sql
select *
where email ilike '[email protected]'
ilike is similar to like but case insensitive. For escape character use replace()
where email ilike replace(replace(replace($1, '~', '~~'), '%', '~%'), '_', '~_') escape '~'
or you could create a function to escape text; for array of text use
where email ilike any(array['[email protected]', '[email protected]'])
Solution 2 - Sql
First, what not to do: don't use ILIKE...
create table y
(
id serial not null,
email text not null unique
);
insert into y(email)
values('[email protected]') ,('[email protected]');
insert into y(email)
select n from generate_series(1,1000) as i(n);
-- no need to create an index on email,
-- UNIQUE constraint on email already makes an index.
-- thanks a_horse_with_no_name
-- create index ix_y on y(email);
explain select * from y
where email ilike
ANY(ARRAY['[email protected]','[email protected]']);
Execution Plan:
memdb=# explain select * from y where email ilike ANY(ARRAY['[email protected]','[email protected]']);
QUERY PLAN
----------------------------------------------------------------------------------------
Seq Scan on y (cost=0.00..17.52 rows=1 width=7)
Filter: (email ~~* ANY ('{[email protected],[email protected]}'::text[]))
(2 rows)
It's either you create an indexed lower expression...
create function lower(t text[]) returns text[]
as
$$
select lower($1::text)::text[]
$$ language sql;
create unique index ix_y_2 on y(lower(email));
explain select * from y
where lower(email) =
ANY(lower(ARRAY['[email protected]','[email protected]']));
...which properly uses index:
memdb=# explain select * from y where lower(email) = ANY(lower(ARRAY['[email protected]','[email protected]']));
QUERY PLAN
--------------------------------------------------------------------------------------------------------------------------------
Bitmap Heap Scan on y (cost=22.60..27.98 rows=10 width=7)
Recheck Cond: (lower(email) = ANY ((lower(('{[email protected],[email protected]}'::text[])::text))::text[]))
-> Bitmap Index Scan on ix_y_2 (cost=0.00..22.60 rows=10 width=0)
Index Cond: (lower(email) = ANY ((lower(('{[email protected],[email protected]}'::text[])::text))::text[]))
(4 rows)
Or you use citext data type...
create table x
(
id serial not null,
email citext not null unique
);
insert into x(email)
values('[email protected]'),('[email protected]');
insert into x(email)
select n from generate_series(1,1000) as i(n);
-- no need to create an index on email,
-- UNIQUE constraint on email already makes an index.
-- thanks a_horse_with_no_name
-- create index ix_x on x(email);
explain select * from x
where email =
ANY(ARRAY['[email protected]','[email protected]']::citext[]);
...which properly uses index even you don't create an index on expression (e.g. create index zzz on yyy(lower(field))):
memdb=# explain select * from x where email = ANY(ARRAY['[email protected]','[email protected]']::citext[]);
QUERY PLAN
--------------------------------------------------------------------------------------------------
Bitmap Heap Scan on x (cost=8.57..13.91 rows=2 width=36)
Recheck Cond: (email = ANY ('{[email protected],[email protected]}'::citext[]))
-> Bitmap Index Scan on x_email_key (cost=0.00..8.57 rows=2 width=0)
Index Cond: (email = ANY ('{[email protected],[email protected]}'::citext[]))
If citext field type is not yet installed, run this:
CREATE EXTENSION IF NOT EXISTS citext WITH SCHEMA public;
Solution 3 - Sql
Things have changed in the last 4 years since this question was answered and the recommendation "don't use ILIKE" isn't true any more (at least in such a general way).
In fact, depending on the data distribution, ILIKE with a trigram index might even be faster then citext.
For a unique index there is indeed big difference, which can be seen when using Michael's test-setup:
create table y
(
id serial not null,
email text not null unique
);
insert into y(email)
select 'some.name'||n||'@foobar.com'
from generate_series(1,100000) as i(n);
-- create a trigram index to support ILIKE
create index ix_y on y using gin (email gin_trgm_ops);
create table x
(
id serial not null,
email citext not null unique
);
-- no need to create an index
-- the UNIQUE constraint will create a regular B-Tree index
insert into x(email)
select email
from y;
The execution plan for using ILIKE:
explain (analyze)
select *
from y
where email ilike ANY (ARRAY['[email protected]','[email protected]']);
Bitmap Heap Scan on y (cost=126.07..154.50 rows=20 width=29) (actual time=60.696..60.818 rows=2 loops=1)
Recheck Cond: (email ~~* ANY ('{[email protected],[email protected]}'::text[]))
Rows Removed by Index Recheck: 13
Heap Blocks: exact=11
-> Bitmap Index Scan on ix_y (cost=0.00..126.07 rows=20 width=0) (actual time=60.661..60.661 rows=15 loops=1)
Index Cond: (email ~~* ANY ('{[email protected],[email protected]}'::text[]))
Planning time: 0.952 ms
Execution time: 61.004 ms
And for using citext:
explain (analyze)
select *
from x
where email = ANY (ARRAY['[email protected]','[email protected]']);
Index Scan using x_email_key on x (cost=0.42..5.85 rows=2 width=29) (actual time=0.111..0.203 rows=2 loops=1)
Index Cond: (email = ANY ('{[email protected],[email protected]}'::citext[]))
Planning time: 0.115 ms
Execution time: 0.254 ms
Note that the ILIKE query is in fact something different then the = query for citext as ILIKE would honor wildcards.
However for a non-unique index things look different. The following setup is based on a recent question asking the same:
create table data
(
group_id serial primary key,
name text
);
create table data_ci
(
group_id serial primary key,
name citext
);
insert into data(name)
select 'data'||i.n
from generate_series(1,1000) as i(n), generate_series(1,1000) as i2(n);
insert into data_ci(group_id, name)
select group_id, name
from data;
create index ix_data_gin on data using gin (name public.gin_trgm_ops);
create index ix_data_ci on data_ci (name);
So we have a million rows in each table and a 1000 distinct values for the name column and for each distinct value we have 1000 duplicates. A query looking for 3 different values will thus return 3000 rows.
In this case the trigram index is substantially faster then the BTree index:
explain (analyze)
select *
from data
where name ilike any (array['Data1', 'data2', 'DATA3']);
Bitmap Heap Scan on data (cost=88.25..1777.61 rows=1535 width=11) (actual time=2.906..11.064 rows=3000 loops=1)
Recheck Cond: (name ~~* ANY ('{Data1,data2,DATA3}'::text[]))
Heap Blocks: exact=17
-> Bitmap Index Scan on ix_data_gin (cost=0.00..87.87 rows=1535 width=0) (actual time=2.869..2.869 rows=3000 loops=1)
Index Cond: (name ~~* ANY ('{Data1,data2,DATA3}'::text[]))
Planning time: 2.174 ms
Execution time: 11.282 ms
And the btree index on the citext column now uses a Seq Scan
explain analyze
select *
from data_ci
where name = any (array['Data1', 'data2', 'DATA3']);
Seq Scan on data_ci (cost=0.00..10156.00 rows=2904 width=11) (actual time=0.449..304.301 rows=1000 loops=1)
Filter: ((name)::text = ANY ('{Data1,data2,DATA3}'::text[]))
Rows Removed by Filter: 999000
Planning time: 0.152 ms
Execution time: 304.360 ms
Also the size of the GIN index is actually smaller then the one on the citext column:
select pg_size_pretty(pg_total_relation_size('ix_data_gin')) as gin_index_size,
pg_size_pretty(pg_total_relation_size('ix_data_ci')) as citex_index_size
gin_index_size | citex_index_size
---------------+-----------------
11 MB | 21 MB
The above was done using Postgres 9.6.1 on a Windows laptop with random_page_cost set to 1.5
Solution 4 - Sql
Use case-insensitive text data type. Use citext:
create table emails
(
user_id int references users(user_id)
email citext
);
insert into emails(user_id, email) values(1, '[email protected]');
insert into emails(user_id, email) values(2, '[email protected]');
select * from emails where email in ('[email protected]','[email protected]');
In case you cannot find the citext.sql in your contrib directory, copy and paste this in your pgAdmin:
/* $PostgreSQL: pgsql/contrib/citext/citext.sql.in,v 1.3 2008/09/05 18:25:16 tgl Exp $ */
-- Adjust this setting to control where the objects get created.
SET search_path = public;
--
-- PostgreSQL code for CITEXT.
--
-- Most I/O functions, and a few others, piggyback on the "text" type
-- functions via the implicit cast to text.
--
--
-- Shell type to keep things a bit quieter.
--
CREATE TYPE citext;
--
-- Input and output functions.
--
CREATE OR REPLACE FUNCTION citextin(cstring)
RETURNS citext
AS 'textin'
LANGUAGE internal IMMUTABLE STRICT;
CREATE OR REPLACE FUNCTION citextout(citext)
RETURNS cstring
AS 'textout'
LANGUAGE internal IMMUTABLE STRICT;
CREATE OR REPLACE FUNCTION citextrecv(internal)
RETURNS citext
AS 'textrecv'
LANGUAGE internal STABLE STRICT;
CREATE OR REPLACE FUNCTION citextsend(citext)
RETURNS bytea
AS 'textsend'
LANGUAGE internal STABLE STRICT;
--
-- The type itself.
--
CREATE TYPE citext (
INPUT = citextin,
OUTPUT = citextout,
RECEIVE = citextrecv,
SEND = citextsend,
INTERNALLENGTH = VARIABLE,
STORAGE = extended,
-- make it a non-preferred member of string type category
CATEGORY = 'S',
PREFERRED = false
);
--
-- Type casting functions for those situations where the I/O casts don't
-- automatically kick in.
--
CREATE OR REPLACE FUNCTION citext(bpchar)
RETURNS citext
AS 'rtrim1'
LANGUAGE internal IMMUTABLE STRICT;
CREATE OR REPLACE FUNCTION citext(boolean)
RETURNS citext
AS 'booltext'
LANGUAGE internal IMMUTABLE STRICT;
CREATE OR REPLACE FUNCTION citext(inet)
RETURNS citext
AS 'network_show'
LANGUAGE internal IMMUTABLE STRICT;
--
-- Implicit and assignment type casts.
--
CREATE CAST (citext AS text) WITHOUT FUNCTION AS IMPLICIT;
CREATE CAST (citext AS varchar) WITHOUT FUNCTION AS IMPLICIT;
CREATE CAST (citext AS bpchar) WITHOUT FUNCTION AS ASSIGNMENT;
CREATE CAST (text AS citext) WITHOUT FUNCTION AS ASSIGNMENT;
CREATE CAST (varchar AS citext) WITHOUT FUNCTION AS ASSIGNMENT;
CREATE CAST (bpchar AS citext) WITH FUNCTION citext(bpchar) AS ASSIGNMENT;
CREATE CAST (boolean AS citext) WITH FUNCTION citext(boolean) AS ASSIGNMENT;
CREATE CAST (inet AS citext) WITH FUNCTION citext(inet) AS ASSIGNMENT;
--
-- Operator Functions.
--
CREATE OR REPLACE FUNCTION citext_eq( citext, citext )
RETURNS bool
AS '$libdir/citext'
LANGUAGE C IMMUTABLE STRICT;
CREATE OR REPLACE FUNCTION citext_ne( citext, citext )
RETURNS bool
AS '$libdir/citext'
LANGUAGE C IMMUTABLE STRICT;
CREATE OR REPLACE FUNCTION citext_lt( citext, citext )
RETURNS bool
AS '$libdir/citext'
LANGUAGE C IMMUTABLE STRICT;
CREATE OR REPLACE FUNCTION citext_le( citext, citext )
RETURNS bool
AS '$libdir/citext'
LANGUAGE C IMMUTABLE STRICT;
CREATE OR REPLACE FUNCTION citext_gt( citext, citext )
RETURNS bool
AS '$libdir/citext'
LANGUAGE C IMMUTABLE STRICT;
CREATE OR REPLACE FUNCTION citext_ge( citext, citext )
RETURNS bool
AS '$libdir/citext'
LANGUAGE C IMMUTABLE STRICT;
--
-- Operators.
--
CREATE OPERATOR = (
LEFTARG = CITEXT,
RIGHTARG = CITEXT,
COMMUTATOR = =,
NEGATOR = <>,
PROCEDURE = citext_eq,
RESTRICT = eqsel,
JOIN = eqjoinsel,
HASHES,
MERGES
);
CREATE OPERATOR <> (
LEFTARG = CITEXT,
RIGHTARG = CITEXT,
NEGATOR = =,
COMMUTATOR = <>,
PROCEDURE = citext_ne,
RESTRICT = neqsel,
JOIN = neqjoinsel
);
CREATE OPERATOR < (
LEFTARG = CITEXT,
RIGHTARG = CITEXT,
NEGATOR = >=,
COMMUTATOR = >,
PROCEDURE = citext_lt,
RESTRICT = scalarltsel,
JOIN = scalarltjoinsel
);
CREATE OPERATOR <= (
LEFTARG = CITEXT,
RIGHTARG = CITEXT,
NEGATOR = >,
COMMUTATOR = >=,
PROCEDURE = citext_le,
RESTRICT = scalarltsel,
JOIN = scalarltjoinsel
);
CREATE OPERATOR >= (
LEFTARG = CITEXT,
RIGHTARG = CITEXT,
NEGATOR = <,
COMMUTATOR = <=,
PROCEDURE = citext_ge,
RESTRICT = scalargtsel,
JOIN = scalargtjoinsel
);
CREATE OPERATOR > (
LEFTARG = CITEXT,
RIGHTARG = CITEXT,
NEGATOR = <=,
COMMUTATOR = <,
PROCEDURE = citext_gt,
RESTRICT = scalargtsel,
JOIN = scalargtjoinsel
);
--
-- Support functions for indexing.
--
CREATE OR REPLACE FUNCTION citext_cmp(citext, citext)
RETURNS int4
AS '$libdir/citext'
LANGUAGE C STRICT IMMUTABLE;
CREATE OR REPLACE FUNCTION citext_hash(citext)
RETURNS int4
AS '$libdir/citext'
LANGUAGE C STRICT IMMUTABLE;
--
-- The btree indexing operator class.
--
CREATE OPERATOR CLASS citext_ops
DEFAULT FOR TYPE CITEXT USING btree AS
OPERATOR 1 < (citext, citext),
OPERATOR 2 <= (citext, citext),
OPERATOR 3 = (citext, citext),
OPERATOR 4 >= (citext, citext),
OPERATOR 5 > (citext, citext),
FUNCTION 1 citext_cmp(citext, citext);
--
-- The hash indexing operator class.
--
CREATE OPERATOR CLASS citext_ops
DEFAULT FOR TYPE citext USING hash AS
OPERATOR 1 = (citext, citext),
FUNCTION 1 citext_hash(citext);
--
-- Aggregates.
--
CREATE OR REPLACE FUNCTION citext_smaller(citext, citext)
RETURNS citext
AS '$libdir/citext'
LANGUAGE 'C' IMMUTABLE STRICT;
CREATE OR REPLACE FUNCTION citext_larger(citext, citext)
RETURNS citext
AS '$libdir/citext'
LANGUAGE 'C' IMMUTABLE STRICT;
CREATE AGGREGATE min(citext) (
SFUNC = citext_smaller,
STYPE = citext,
SORTOP = <
);
CREATE AGGREGATE max(citext) (
SFUNC = citext_larger,
STYPE = citext,
SORTOP = >
);
--
-- CITEXT pattern matching.
--
CREATE OR REPLACE FUNCTION texticlike(citext, citext)
RETURNS bool AS 'texticlike'
LANGUAGE internal IMMUTABLE STRICT;
CREATE OR REPLACE FUNCTION texticnlike(citext, citext)
RETURNS bool AS 'texticnlike'
LANGUAGE internal IMMUTABLE STRICT;
CREATE OR REPLACE FUNCTION texticregexeq(citext, citext)
RETURNS bool AS 'texticregexeq'
LANGUAGE internal IMMUTABLE STRICT;
CREATE OR REPLACE FUNCTION texticregexne(citext, citext)
RETURNS bool AS 'texticregexne'
LANGUAGE internal IMMUTABLE STRICT;
CREATE OPERATOR ~ (
PROCEDURE = texticregexeq,
LEFTARG = citext,
RIGHTARG = citext,
NEGATOR = !~,
RESTRICT = icregexeqsel,
JOIN = icregexeqjoinsel
);
CREATE OPERATOR ~* (
PROCEDURE = texticregexeq,
LEFTARG = citext,
RIGHTARG = citext,
NEGATOR = !~*,
RESTRICT = icregexeqsel,
JOIN = icregexeqjoinsel
);
CREATE OPERATOR !~ (
PROCEDURE = texticregexne,
LEFTARG = citext,
RIGHTARG = citext,
NEGATOR = ~,
RESTRICT = icregexnesel,
JOIN = icregexnejoinsel
);
CREATE OPERATOR !~* (
PROCEDURE = texticregexne,
LEFTARG = citext,
RIGHTARG = citext,
NEGATOR = ~*,
RESTRICT = icregexnesel,
JOIN = icregexnejoinsel
);
CREATE OPERATOR ~~ (
PROCEDURE = texticlike,
LEFTARG = citext,
RIGHTARG = citext,
NEGATOR = !~~,
RESTRICT = iclikesel,
JOIN = iclikejoinsel
);
CREATE OPERATOR ~~* (
PROCEDURE = texticlike,
LEFTARG = citext,
RIGHTARG = citext,
NEGATOR = !~~*,
RESTRICT = iclikesel,
JOIN = iclikejoinsel
);
CREATE OPERATOR !~~ (
PROCEDURE = texticnlike,
LEFTARG = citext,
RIGHTARG = citext,
NEGATOR = ~~,
RESTRICT = icnlikesel,
JOIN = icnlikejoinsel
);
CREATE OPERATOR !~~* (
PROCEDURE = texticnlike,
LEFTARG = citext,
RIGHTARG = citext,
NEGATOR = ~~*,
RESTRICT = icnlikesel,
JOIN = icnlikejoinsel
);
--
-- Matching citext to text.
--
CREATE OR REPLACE FUNCTION texticlike(citext, text)
RETURNS bool AS 'texticlike'
LANGUAGE internal IMMUTABLE STRICT;
CREATE OR REPLACE FUNCTION texticnlike(citext, text)
RETURNS bool AS 'texticnlike'
LANGUAGE internal IMMUTABLE STRICT;
CREATE OR REPLACE FUNCTION texticregexeq(citext, text)
RETURNS bool AS 'texticregexeq'
LANGUAGE internal IMMUTABLE STRICT;
CREATE OR REPLACE FUNCTION texticregexne(citext, text)
RETURNS bool AS 'texticregexne'
LANGUAGE internal IMMUTABLE STRICT;
CREATE OPERATOR ~ (
PROCEDURE = texticregexeq,
LEFTARG = citext,
RIGHTARG = text,
NEGATOR = !~,
RESTRICT = icregexeqsel,
JOIN = icregexeqjoinsel
);
CREATE OPERATOR ~* (
PROCEDURE = texticregexeq,
LEFTARG = citext,
RIGHTARG = text,
NEGATOR = !~*,
RESTRICT = icregexeqsel,
JOIN = icregexeqjoinsel
);
CREATE OPERATOR !~ (
PROCEDURE = texticregexne,
LEFTARG = citext,
RIGHTARG = text,
NEGATOR = ~,
RESTRICT = icregexnesel,
JOIN = icregexnejoinsel
);
CREATE OPERATOR !~* (
PROCEDURE = texticregexne,
LEFTARG = citext,
RIGHTARG = text,
NEGATOR = ~*,
RESTRICT = icregexnesel,
JOIN = icregexnejoinsel
);
CREATE OPERATOR ~~ (
PROCEDURE = texticlike,
LEFTARG = citext,
RIGHTARG = text,
NEGATOR = !~~,
RESTRICT = iclikesel,
JOIN = iclikejoinsel
);
CREATE OPERATOR ~~* (
PROCEDURE = texticlike,
LEFTARG = citext,
RIGHTARG = text,
NEGATOR = !~~*,
RESTRICT = iclikesel,
JOIN = iclikejoinsel
);
CREATE OPERATOR !~~ (
PROCEDURE = texticnlike,
LEFTARG = citext,
RIGHTARG = text,
NEGATOR = ~~,
RESTRICT = icnlikesel,
JOIN = icnlikejoinsel
);
CREATE OPERATOR !~~* (
PROCEDURE = texticnlike,
LEFTARG = citext,
RIGHTARG = text,
NEGATOR = ~~*,
RESTRICT = icnlikesel,
JOIN = icnlikejoinsel
);
--
-- Matching citext in string comparison functions.
-- XXX TODO Ideally these would be implemented in C.
--
CREATE OR REPLACE FUNCTION regexp_matches( citext, citext ) RETURNS TEXT[] AS $$
SELECT pg_catalog.regexp_matches( $1::pg_catalog.text, $2::pg_catalog.text, 'i' );
$$ LANGUAGE SQL IMMUTABLE STRICT;
CREATE OR REPLACE FUNCTION regexp_matches( citext, citext, text ) RETURNS TEXT[] AS $$
SELECT pg_catalog.regexp_matches( $1::pg_catalog.text, $2::pg_catalog.text, CASE WHEN pg_catalog.strpos($3, 'c') = 0 THEN $3 || 'i' ELSE $3 END );
$$ LANGUAGE SQL IMMUTABLE STRICT;
CREATE OR REPLACE FUNCTION regexp_replace( citext, citext, text ) returns TEXT AS $$
SELECT pg_catalog.regexp_replace( $1::pg_catalog.text, $2::pg_catalog.text, $3, 'i');
$$ LANGUAGE SQL IMMUTABLE STRICT;
CREATE OR REPLACE FUNCTION regexp_replace( citext, citext, text, text ) returns TEXT AS $$
SELECT pg_catalog.regexp_replace( $1::pg_catalog.text, $2::pg_catalog.text, $3, CASE WHEN pg_catalog.strpos($4, 'c') = 0 THEN $4 || 'i' ELSE $4 END);
$$ LANGUAGE SQL IMMUTABLE STRICT;
CREATE OR REPLACE FUNCTION regexp_split_to_array( citext, citext ) RETURNS TEXT[] AS $$
SELECT pg_catalog.regexp_split_to_array( $1::pg_catalog.text, $2::pg_catalog.text, 'i' );
$$ LANGUAGE SQL IMMUTABLE STRICT;
CREATE OR REPLACE FUNCTION regexp_split_to_array( citext, citext, text ) RETURNS TEXT[] AS $$
SELECT pg_catalog.regexp_split_to_array( $1::pg_catalog.text, $2::pg_catalog.text, CASE WHEN pg_catalog.strpos($3, 'c') = 0 THEN $3 || 'i' ELSE $3 END );
$$ LANGUAGE SQL IMMUTABLE STRICT;
CREATE OR REPLACE FUNCTION regexp_split_to_table( citext, citext ) RETURNS SETOF TEXT AS $$
SELECT pg_catalog.regexp_split_to_table( $1::pg_catalog.text, $2::pg_catalog.text, 'i' );
$$ LANGUAGE SQL IMMUTABLE STRICT;
CREATE OR REPLACE FUNCTION regexp_split_to_table( citext, citext, text ) RETURNS SETOF TEXT AS $$
SELECT pg_catalog.regexp_split_to_table( $1::pg_catalog.text, $2::pg_catalog.text, CASE WHEN pg_catalog.strpos($3, 'c') = 0 THEN $3 || 'i' ELSE $3 END );
$$ LANGUAGE SQL IMMUTABLE STRICT;
CREATE OR REPLACE FUNCTION strpos( citext, citext ) RETURNS INT AS $$
SELECT pg_catalog.strpos( pg_catalog.lower( $1::pg_catalog.text ), pg_catalog.lower( $2::pg_catalog.text ) );
$$ LANGUAGE SQL IMMUTABLE STRICT;
CREATE OR REPLACE FUNCTION replace( citext, citext, citext ) RETURNS TEXT AS $$
SELECT pg_catalog.regexp_replace( $1::pg_catalog.text, pg_catalog.regexp_replace($2::pg_catalog.text, '([^a-zA-Z_0-9])', E'\\\\\\1', 'g'), $3::pg_catalog.text, 'gi' );
$$ LANGUAGE SQL IMMUTABLE STRICT;
CREATE OR REPLACE FUNCTION split_part( citext, citext, int ) RETURNS TEXT AS $$
SELECT (pg_catalog.regexp_split_to_array( $1::pg_catalog.text, pg_catalog.regexp_replace($2::pg_catalog.text, '([^a-zA-Z_0-9])', E'\\\\\\1', 'g'), 'i'))[$3];
$$ LANGUAGE SQL IMMUTABLE STRICT;
CREATE OR REPLACE FUNCTION translate( citext, citext, text ) RETURNS TEXT AS $$
SELECT pg_catalog.translate( pg_catalog.translate( $1::pg_catalog.text, pg_catalog.lower($2::pg_catalog.text), $3), pg_catalog.upper($2::pg_catalog.text), $3);
$$ LANGUAGE SQL IMMUTABLE STRICT;
Solution 5 - Sql
You can also create an index on lower(email).
Solution 6 - Sql
From PostgreSQL v12 on, you can create a case insensitive ICU collation (if PostgreSQL has been built with ICU support):
CREATE COLLATION english_ci (
PROVIDER = 'icu',
LOCALE = 'en-US@colStrength=secondary',
DETERMINISTIC = FALSE
);
You can use that in column definitions:
ALTER TABLE users ALTER email TYPE text COLLATE english_ci;
Or you can use it in comparisons or ORDER BY clauses:
WHERE email COLLATE english_ci IN ('[email protected]', '[email protected]')