String Functions and Operators

This section describes functions and operators for examining and manipulating string values. Strings in this context include values of the types character, character varying, and text. Except where noted, these functions and operators are declared to accept and return type text. They will interchangeably accept character varying arguments. Values of type character will be converted to text before the function or operator is applied, resulting in stripping any trailing spaces in the character value.

SQL defines some string functions that use key words, rather than commas, to separate arguments. Details are in Section SQL String Functions and Operators. QHB also provides versions of these functions that use the regular function invocation syntax (see Section Other String Functions and Operators).

Note
The string concatenation operator (||) will accept non-string input, so long as at least one input is of string type, as shown in Section SQL String Functions and Operators. For other cases, inserting an explicit coercion to text can be used to have non-string input accepted.

SQL String Functions and Operators

text || text → text

Concatenates the two strings.

'Quan' || 'tum' → Quantum

text || anynonarray → text

anynonarray || text → text

Converts the non-string input to text, then concatenates the two strings. (The non-string input cannot be of an array type, because that would create ambiguity with the array || operators. If you want to concatenate an array's text equivalent, cast it to text explicitly.)

'Value: ' || 42 → Value: 42

btrim

btrim ( stringtext [,characters text ] ) → text

Removes the longest string containing only characters in characters (a space by default) from the start and end of string.

btrim('xyxtrimyyx', 'xyz') → trim

text IS NORMALIZED

text IS [NOT] [form] NORMALIZED → boolean

Checks whether the string is in the specified Unicode normalization form. The optional form key word specifies the form: NFC (the default), NFD, NFKC, or NFKD. This expression can only be used when the server encoding is UTF8. Note that checking for normalization using this expression is often faster than normalizing possibly already normalized strings.

U&'\0061\0308bc' IS NFD NORMALIZED → t

bit_length

bit_length ( text ) → integer

Returns number of bits in the string (8 times the octet_length).

bit_length('jose') → 32

char(acter)_length

char_length ( text ) → integer
character_length ( text ) → integer

Returns number of characters in the string.

char_length('josé') → 4

lower

lower ( text ) → text

Converts the string to all lower case, according to the rules of the database's locale.

lower('TOM') → tom

lpad

lpad ( stringtext,lengthinteger [,fill text ] ) → text

Extends the string to length length by prepending the characters fill (a space by default). If the string is already longer than length then it is truncated (on the right).

lpad('hi', 5, 'xy') → xyxhi

ltrim

ltrim ( stringtext [,characters text ] ) → text

Removes the longest string containing only characters in characters (a space by default) from the start of string.

ltrim('zzzytest', 'xyz') → test

normalize

normalize ( text [, form ] ) → text

Converts the string to the specified Unicode normalization form. The optional form key word specifies the form: NFC (по умолчанию), NFD, NFKC, or NFKD. This function can only be used when the server encoding is UTF8.

normalize(U&'\0061\0308bc', NFC) → U&'\00E4bc'

octet_length

octet_length ( text ) → integer

Returns number of bytes in the string.

octet_length('josé') → 5

(if server encoding is UTF8)

octet_length ( character ) → integer

Returns number of bytes in the string. Since this version of the function accepts type character directly, it will not strip trailing spaces.

octet_length('abc '::character(4)) → 4

overlay

overlay ( stringtext PLACINGnewsubstringtext FROMstartinteger [ FORcount integer ] ) → text

Replaces the substring of string that starts at the start'th character and extends for count characters with newsubstring. If count is omitted, it defaults to the length of newsubstring.

overlay('Txxxxas' placing 'hom' from 2 for 4) → Thomas

position

position ( substringtext INstring text ) → integer

Returns first starting index of the specified substring within string, or zero if it's not present.

position('om' in 'Thomas') → 3

rpad

rpad ( stringtext,lengthinteger [,fill text ] ) → text

Extends the string to length length by appending the characters fill (a space by default). If the string is already longer than length then it is truncated.

rpad('hi', 5, 'xy') → hixyx

rtrim

rtrim ( stringtext [,characters text ] ) → text

Removes the longest string containing only characters in characters (a space by default) from the end of string.

rtrim('testxxzx', 'xyz') → test

substring

substring ( stringtext [ FROMstartinteger ] [ FORcount integer ] ) → text

Extracts the substring of string starting at the start'th character if that is specified, and stopping after count characters if that is specified. Provide at least one of start and count.

substring('Thomas' from 2 for 3) → hom

substring('Thomas' from 3) → omas

substring('Thomas' for 2) → Th

substring ( stringtext FROMpattern text ) → text

Extracts the first substring matching POSIX regular expression; see Section POSIX Regular Expressions.

substring('Thomas' from '...$') → mas

substring ( stringtext SIMILARpatterntext ESCAPEescape text ) → text
substring ( stringtext FROMpatterntext FORescape text ) → text

Extracts the first substring matching SQL regular expression; see Section SIMILAR TO Regular Expressions. The first form has been specified since SQL:2003; the second form was only in SQL:1999 and should be considered obsolete.

substring('Thomas' similar '%#"o_a#"_' escape '#') → oma

trim

trim ( [ LEADING | TRAILING | BOTH ] [ characterstext ] FROMstring text ) → text

Removes the longest string containing only characters in characters (a space by default) from the start, end, or both ends (BOTH is the default) of string.

trim(both 'xyz' from 'yxTomxx') → Tom

trim ( [ LEADING | TRAILING | BOTH ] [ FROM ] stringtext [,characters text ] ) → text

This is a non-standard syntax for trim().

trim(both 'xyz' from 'yxTomxx') → Tom

upper

upper ( text ) → text

Converts the string to all upper case, according to the rules of the database's locale.

upper('tom') → TOM

Other String Functions and Operators

Additional string manipulation functions and operators are available and are listed in this section. (Some of these are used internally to implement the SQL-standard string functions listed in Section SQL String Functions and Operators.) There are also pattern-matching operators, which are described in Section Pattern Matching, and operators for full-text search, which are described in Chapter Full Text Search.

text ^@ text → boolean

Returns true if the first string starts with the second string (equivalent to the starts_with() function).

'alphabet' ^@ 'alph' → t

ascii

ascii ( text ) → integer

Returns the numeric code of the first character of the argument. In UTF8 encoding, returns the Unicode code point of the character. In other multibyte encodings, the argument must be an ASCII character.

ascii('x') → 120

chr

chr ( integer ) → text

Returns the character with the given code. In UTF8 encoding the argument is treated as a Unicode code point. In other multibyte encodings the argument must designate an ASCII character. chr(0) is disallowed because text data types cannot store that character.

chr(65) → A

concat

concat ( val1"any" [,val2 "any" [, ...] ] ) → text

Concatenates the text representations of all the arguments. NULL arguments are ignored.

concat('abcde', 2, NULL, 22) → abcde222

concat_ws

concat_ws ( septext,val1"any" [,val2 "any" [, ...] ] ) → text

Concatenates all but the first argument, with separators. The first argument is used as the separator string, and should not be NULL. Other NULL arguments are ignored.

concat_ws(',', 'abcde', 2, NULL, 22) → abcde,2,22

format

format ( formatstrtext [,formatarg "any" [, ...] ] ) → text

Formats arguments according to a format string; see Section The Function format. This function is similar to the C function sprintf.

format('Hello %s, %1$s', 'World') → Hello World, World

initcap

initcap ( text ) → text

Converts the first letter of each word to upper case and the rest to lower case. Words are sequences of alphanumeric characters separated by non-alphanumeric characters.

initcap('hi THOMAS') → Hi Thomas

left

left ( stringtext,n integer ) → text

Returns first n characters in the string, or when n is negative, returns all but last |n| characters.

left('abcde', 2) → ab

length

length ( text ) → integer

Returns the number of characters in the string.

length('jose') → 4

lpad

lpad ( stringtext,lengthinteger [,fill text ] ) → text

Extends the string to length length by prepending the characters fill (a space by default). If the string is already longer than length then it is truncated (on the right).

lpad('hi', 5, 'xy') → xyxhi

ltrim

ltrim ( stringtext [,characters text ] ) → text

Removes the longest string containing only characters in characters (a space by default) from the start of string.

ltrim('zzzytest', 'xyz') → test

md5

md5 ( text ) → text

Computes the MD5 hash of the argument, with the result written in hexadecimal.

md5('abc') → 900150983cd24fb0d6963f7d28e17f72

parse_ident

parse_ident ( qualified_identifiertext [,strict_mode boolean DEFAULT true ] ) → text[]

Splits qualified_identifier into an array of identifiers, removing any quoting of individual identifiers. By default, extra characters after the last identifier are considered an error; but if the second parameter is false, then such extra characters are ignored. (This behavior is useful for parsing names for objects like functions.) Note that this function does not truncate over-length identifiers. If you want truncation you can cast the result to name[].

parse_ident('"SomeSchema".someTable') → {SomeSchema,sometable}

pg_client_encoding

pg_client_encoding ( ) → name

Returns current client encoding name.

pg_client_encoding() → UTF8

quote_ident

quote_ident ( text ) → text

Returns the given string suitably quoted to be used as an identifier in an SQL statement string. Quotes are added only if necessary (i.e., if the string contains non-identifier characters or would be case-folded). Embedded quotes are properly doubled. See also Example Quoting Values in Dynamic Queries.

quote_ident('Foo bar') → "Foo bar"

quote_literal

quote_literal ( text ) → text

Returns the given string suitably quoted to be used as a string literal in an SQL statement string. Embedded single-quotes and backslashes are properly doubled. Note that quote_literal returns null on null input; if the argument might be null, quote_nullable is often more suitable. See also Example Quoting Values in Dynamic Queries.

quote_literal(E'O\'Reilly') → 'O''Reilly'

quote_literal ( anyelement ) → text

Converts the given value to text and then quotes it as a literal. Embedded single-quotes and backslashes are properly doubled.

quote_literal(42.5) → '42.5'

quote_nullable

quote_nullable ( text ) → text

Returns the given string suitably quoted to be used as a string literal in an SQL statement string; or, if the argument is null, returns NULL. Embedded single- quotes and backslashes are properly doubled. See also Example Quoting Values in Dynamic Queries.

quote_nullable(NULL) → NULL

quote_nullable ( anyelement ) → text

Converts the given value to text and then quotes it as a literal; or, if the argument is null, returns NULL. Embedded single-quotes and backslashes are properly doubled.

quote_nullable(42.5) → '42.5'

regexp_count

regexp_count ( stringtext,patterntext [,startinteger [,flags text ]] ) → integer

Returns the number of times the POSIX regular expression pattern matches in the string; see Section POSIX Regular Expressions.

regexp_count('123456789012', '\d\d\d', 2) → 3

regexp_instr

regexp_instr ( stringtext,patterntext [,startinteger [,Ninteger [,endoptioninteger [,flagstext [,subexpr integer ] ] ] ] ] ) → integer

Returns the position within строке where the N'th match of the POSIX regular expression pattern occurs, or zero if there is no such match; see Section POSIX Regular Expressions.

regexp_instr('ABCDEF', 'c(.)(..)', 1, 1, 0, 'i') → 3

regexp_instr('ABCDEF', 'c(.)(..)', 1, 1, 0, 'i', 2) → 5

regexp_like

regexp_like ( stringtext,patterntext [,flags text ] ) → boolean

Checks whether a match of the POSIX regular expression pattern occurs within string; see Section POSIX Regular Expressions.

regexp_like('Hello World', 'world$', 'i') → t

regexp_match

regexp_match ( stringtext,patterntext [,flags text ] ) → text[]

Returns substrings within the first match of the POSIX regular expression pattern to the string; see Section POSIX Regular Expressions.

regexp_match('foobarbequebaz', '(bar)(beque)') → {bar,beque}

regexp_matches

regexp_matches ( stringtext,patterntext [,flags text ] ) → setof text[]

Returns substrings within the first match of the POSIX regular expression pattern to the string or substrings within all such matches if the g flag is used; see Section POSIX Regular Expressions.

regexp_matches('foobarbequebaz', 'ba.', 'g') →

     {bar}
     {baz}

regexp_replace

regexp_replace ( stringtext,patterntext,replacementtext [,startinteger ] [,flags text ] ) → text

Replaces the substring that is the first match to the POSIX regular expression pattern, or all such matches if the g flag is used; see Section POSIX Regular Expressions.

regexp_replace('Thomas', '.[mN]a.', 'M') → ThM

regexp_replace ( stringtext,patterntext,replacementtext,startinteger,Ninteger [,flags text ] ) → text

Replaces the substring that is the N'th match to the POSIX regular expression pattern, or all such matches if N is zero; see Section POSIX Regular Expressions.

regexp_replace('Thomas', '.', 'X', 3, 2) → ThoXas

regexp_split_to_array

regexp_split_to_array ( stringtext,patterntext [,flags text ] ) → text[]

Splits string using a POSIX regular expression as the delimiter, producing an array of results; see Section POSIX Regular Expressions.

regexp_split_to_array('hello world', '\s+') → {hello,world}

regexp_split_to_table

regexp_split_to_table ( stringtext,patterntext [,flags text ] ) → setof text

Splits string using a POSIX regular expression as the delimiter, producing a set of results; see Section POSIX Regular Expressions.

regexp_split_to_table('hello world', '\s+') →

     hello
     world

regexp_substr

regexp_substr ( stringtext,patterntext [,startinteger [,Ninteger [,flagstext [,subexpr integer ] ] ] ] ) → text

Returns the substring within string that matches the N'th occurrence of the POSIX regular expression pattern, or NULL if there is no such match; see Section POSIX Regular Expressions.

regexp_substr('ABCDEF', 'c(.)(..)', 1, 1, 'i') → CDEF

regexp_substr('ABCDEF', 'c(.)(..)', 1, 1, 'i', 2) → EF

repeat

repeat ( stringtext,number integer ) → text

Repeats string the specified number of times.

repeat('Pg', 4) → PgPgPgPg

replace

replace ( stringtext,fromtext,to text ) → text

Replaces all occurrences in string of substring from with substring to.

replace('abcdefabcdef', 'cd', 'XX') → abXXefabXXef

reverse

reverse ( text ) → text

Reverses the order of the characters in the string.

reverse('abcde') → edcba

right

right ( stringtext,n integer ) → text

Returns last n characters in the string, or when n is negative, returns all but first |n| characters.

right('abcde', 2) → de

rpad

rpad ( stringtext,lengthinteger [,fill text ] ) → text

Extends the string to length length by appending the characters fill (a space by default). If the string is already longer than length then it is truncated.

rpad('hi', 5, 'xy') → hixyx

rtrim

rtrim ( stringtext [,characters text ] ) → text

Removes the longest string containing only characters in characters (a space by default) from the end of string.

rtrim('testxxzx', 'xyz') → test

split_part

split_part ( stringtext,delimitertext,n integer ) → text

Splits string at occurrences of delimiter and returns the n'th field (counting from one), or when n is negative, returns the |n|'th-from-last field.

split_part('abc~@~def~@~ghi', '~@~', 2) → def

split_part('abc,def,ghi,jkl', ',', -2) → ghi

starts_with

starts_with ( stringtext,prefix text ) → boolean

Returns true if string starts with prefix.

starts_with('alphabet', 'alph') → t

string_to_array

string_to_array ( stringtext,delimitertext [,null_string text ] ) → text[]

Splits the string at occurrences of delimiter and forms the resulting fields into a text array. If delimiter is NULL, each character in the string will become a separate element in the array. If delimiter is an empty string, then the string is treated as a single field. If null_string is supplied and is not NULL, fields matching that string are replaced by NULL. See also array_to_string.

string_to_array('xx~yy~zz', '~', 'yy') → {xx,NULL,zz}

string_to_table

string_to_table ( stringtext,delimitertext [,null_string text ] ) → setof text

Splits the string at occurrences of delimiter and returns the resulting fields as a set of text rows. If delimiter is NULL, each character in the string will become a separate row of the result. If delimiter is an empty string, then the string is treated as a single field. If null_string is supplied and is not NULL, fields matching that string are replaced by NULL.

string_to_table('xx~^~yy~^~zz', '~^~', 'yy') →

    xx
    NULL
    zz

strpos

strpos ( stringtext,substring text ) → integer

Returns first starting index of the specified substring within string, or zero if it's not present. (Same as position(substring in string), but note the reversed argument order.)

strpos('high', 'ig') → 2

substr

substr ( stringtext,startinteger [,count integer ] ) → text

Extracts the substring of string starting at the start'th character, and extending for count characters if that is specified. (Same as substring(string from start for count).)

substr('alphabet', 3) → phabet

substr('alphabet', 3, 2) → ph

to_ascii

to_ascii ( string text ) → text
to_ascii ( stringtext,encoding name ) → text
to_ascii ( stringtext,encoding integer ) → text

Converts строку to ASCII from another encoding, which may be identified by name or number. If encoding is omitted the database encoding is assumed (which in practice is the only useful case). The conversion consists primarily of dropping accents. Conversion is only supported from LATIN1, LATIN2, LATIN9, and WIN1250 encodings. (See the unaccent module for another, more flexible solution.)

to_ascii('Karél') → Karel

to_hex

to_hex ( integer ) → text
to_hex ( bigint ) → text

Converts the number to its equivalent hexadecimal representation.

to_hex(2147483647) → 7fffffff

translate

translate ( stringtext,fromtext,to text ) → text

Replaces each character in string that matches a character in the from set with the corresponding character in the to set. If from is longer than to, occurrences of the extra characters in from are deleted.

translate('12345', '143', 'ax') → a2x5

unistr

unistr ( text ) → text

Evaluate escaped Unicode characters in the argument. Unicode characters can be specified as \XXXX (4 hexadecimal digits), \+XXXXXX (6 hexadecimal digits), \uXXXX (4 hexadecimal digits), or \UXXXXXXXX (8 hexadecimal digits). To specify a backslash, write two backslashes. All other characters are taken literally.

If the server encoding is not UTF-8, the Unicode code point identified by one of these escape sequences is converted to the actual server encoding; an error is reported if that's not possible.

This function provides a (non-standard) alternative to string constants with Unicode escapes (see Section String Constants With Unicode Escapes).

unistr('d\0061t\+000061') → data

unistr('d\u0061t\U00000061') → data

Notes

The concat, concat_ws and format functions are variadic, so it is possible to pass the values to be concatenated or formatted as an array marked with the VARIADIC keyword (see Section SQL Functions with Variable Numbers of Arguments). The array's elements are treated as if they were separate ordinary arguments to the function. If the variadic array argument is NULL, concat and concat_ws return NULL, but format treats a NULL as a zero-element array.

See also the aggregate function string_agg in Section Aggregate Functions, and the functions for converting between strings and the bytea type in Section Text/Binary String Conversion Functions.

The Function format

The function format produces output formatted according to a format string, in a style similar to the C function sprintf.

format(formatstr text [, formatarg "any" [, ...] ])

formatstr is a format string that specifies how the result should be formatted. Text in the format string is copied directly to the result, except where format specifiers are used. Format specifiers act as placeholders in the string, defining how subsequent function arguments should be formatted and inserted into the result. Each formatarg argument is converted to text according to the usual output rules for its data type, and then formatted and inserted into the result string according to the format specifier(s).

Format specifiers are introduced by a % character and have the form

%[позиция][флаги][ширина]тип

where the component fields are:

position (optional)
A string of the form n$ where n is the index of the argument to print. Index 1 means the first argument after formatstr. If the position is omitted, the default is to use the next argument in sequence.

flags (optional)
Additional options controlling how the format specifier's output is formatted. Currently the only supported flag is a minus sign (-) which will cause the format specifier's output to be left-justified. This has no effect unless the width field is also specified.

width (optional)
Specifies the minimum number of characters to use to display the format specifier's output. The output is padded on the left or right (depending on the - flag) with spaces as needed to fill the width. A too-small width does not cause truncation of the output, but is simply ignored. The width may be specified using any of the following: a positive integer; an asterisk (*) to use the next function argument as the width; or a string of the form *n$ to use the nth function argument as the width.
If the width comes from a function argument, that argument is consumed before the argument that is used for the format specifier's value. If the width argument is negative, the result is left aligned (as if the - flag had been specified) within a field of length abs(width).

type (required)
The type of format conversion to use to produce the format specifier's output. The following types are supported:

s formats the argument value as a simple string. A null value is treated as an empty string.
I treats the argument value as an SQL identifier, double-quoting it if necessary. It is an error for the value to be null (equivalent to quote_ident).
L quotes the argument value as an SQL literal. A null value is displayed as the string NULL, without quotes (equivalent to quote_nullable).

In addition to the format specifiers described above, the special sequence %% may be used to output a literal % character.

Here are some examples of the basic format conversions:

SELECT format('Hello% s', 'World');
Result: Hello World

SELECT format('Testing %s, %s, %s, %%', 'one', 'two', 'three');
Result: Testing one, two, three, %

SELECT format('INSERT INTO %I VALUES(%L)', 'Foo bar', E'O\'Reilly');
Result: INSERT INTO "Foo bar" VALUES('O''Reilly')

SELECT format('INSERT INTO %I VALUES(%L)', 'locations', 'C:\Program Files');
Result: INSERT INTO locations VALUES('C:\Program Files')

Here are examples using width fields and the - flag:

SELECT format('|%10s|', 'foo');
Result: |       foo|

SELECT format('|%-10s|', 'foo');
Result: |foo       |

SELECT format('|%*s|', 10, 'foo');
Result: |       foo|

SELECT format('|%*s|', -10, 'foo');
Result: |foo       |

SELECT format('|%-*s|', 10, 'foo');
Result: |foo       |

SELECT format('|%-*s|', -10, 'foo');
Result: |foo       |

These examples show use of position fields:

SELECT format('Testing %3$s, %2$s, %1$s', 'one', 'two', 'three');
Result: Testing three, two, one

SELECT format('|%*2$s|', 'foo', 10, 'bar');
Result: |       bar|

SELECT format('|%1$*2$s|', 'foo', 10, 'bar');
Result: |       foo|

Unlike the standard C function sprintf, QHB's format function allows format specifiers with and without position fields to be mixed in the same format string. A format specifier without a position field always uses the next argument after the last argument consumed. In addition, the format function does not require all function arguments to be used in the format string. For example:

SELECT format('Testing %3$s, %2$s, %s', 'one', 'two', 'three');
Result: Testing three, two, three

The %I and %L format specifiers are particularly useful for safely constructing dynamic SQL statements. See Example Quoting Values in Dynamic Queries.