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 . PostgreSQL also provides versions of these functions that use the regular function invocation syntax (see ). The string concatenation operator (||) will accept non-string input, so long as at least one input is of string type, as shown in . For other cases, inserting an explicit coercion to text can be used to have non-string input accepted. Function/Operator Description Example(s) character string concatenation text || text text Concatenates the two strings. 'Post' || 'greSQL' PostgreSQL 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 ( string text , 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 normalized Unicode normalization 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_length character string length length of a character string character string, length char_length ( text ) integer character_length 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 ( string text, length integer , 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 ( string text , 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 Unicode normalization normalize ( text , form ) text Converts the string to the specified Unicode normalization form. The optional form key word specifies the form: NFC (the default), 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 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 ( string text PLACING newsubstring text FROM start integer FOR count 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 ( substring text IN string 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 ( string text, length integer , 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 ( string text , 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 ( string text FROM start integer FOR count 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 ( string text FROM pattern text ) text Extracts the first substring matching POSIX regular expression; see . substring('Thomas' from '...$') mas substring ( string text SIMILAR pattern text ESCAPE escape text ) text substring ( string text FROM pattern text FOR escape text ) text Extracts the first substring matching SQL regular expression; see . 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 characters text FROM string 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 string text , characters text ) text This is a non-standard syntax for trim(). trim(both from 'yxTomxx', 'xyz') Tom unicode_assigned unicode_assigned ( text ) boolean Returns true if all characters in the string are assigned Unicode codepoints; false otherwise. This function can only be used when the server encoding is UTF8. upper upper ( text ) text Converts the string to all upper case, according to the rules of the database's locale. upper('tom') TOM Additional string manipulation functions and operators are available and are listed in . (Some of these are used internally to implement the SQL-standard string functions listed in .) There are also pattern-matching operators, which are described in , and operators for full-text search, which are described in . Function/Operator Description Example(s) character string prefix test 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 ( sep text, 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 ( formatstr text , formatarg "any" , ... ) text Formats arguments according to a format string; see . 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. When using the libc locale provider, words are sequences of alphanumeric characters separated by non-alphanumeric characters; when using the ICU locale provider, words are separated according to Unicode Standard Annex #29. initcap('hi THOMAS') Hi Thomas casefold casefold ( text ) text Performs case folding of the input string according to the collation. Case folding is similar to case conversion, but the purpose of case folding is to facilitate case-insensitive matching of strings, whereas the purpose of case conversion is to convert to a particular cased form. This function can only be used when the server encoding is UTF8. Ordinarily, case folding simply converts to lowercase, but there may be exceptions depending on the collation. For instance, some characters have more than two lowercase variants, or fold to uppercase. Case folding may change the length of the string. For instance, in the PG_UNICODE_FAST collation, ß (U+00DF) folds to ss. casefold can be used for Unicode Default Caseless Matching. It does not always preserve the normalized form of the input string (see ). The libc provider doesn't support case folding, so casefold is identical to . left left ( string text, 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 md5 md5 ( text ) text Computes the MD5 hash of the argument, with the result written in hexadecimal. md5('abc') 900150983cd24fb0&zwsp;d6963f7d28e17f72 parse_ident parse_ident ( qualified_identifier text , 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 . 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 . 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 . 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 ( string text, pattern text , start integer , flags text ) integer Returns the number of times the POSIX regular expression pattern matches in the string; see . regexp_count('123456789012', '\d\d\d', 2) 3 regexp_instr regexp_instr ( string text, pattern text , start integer , N integer , endoption integer , flags text , subexpr integer ) integer Returns the position within string where the N'th match of the POSIX regular expression pattern occurs, or zero if there is no such match; see . regexp_instr('ABCDEF', 'c(.)(..)', 1, 1, 0, 'i') 3 regexp_instr('ABCDEF', 'c(.)(..)', 1, 1, 0, 'i', 2) 5 regexp_like regexp_like ( string text, pattern text , flags text ) boolean Checks whether a match of the POSIX regular expression pattern occurs within string; see . regexp_like('Hello World', 'world$', 'i') t regexp_match regexp_match ( string text, pattern text , flags text ) text[] Returns substrings within the first match of the POSIX regular expression pattern to the string; see . regexp_match('foobarbequebaz', '(bar)(beque)') {bar,beque} regexp_matches regexp_matches ( string text, pattern text , 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 . regexp_matches('foobarbequebaz', 'ba.', 'g') {bar} {baz} regexp_replace regexp_replace ( string text, pattern text, replacement text , 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 . regexp_replace('Thomas', '.[mN]a.', 'M') ThM regexp_replace ( string text, pattern text, replacement text, start integer , N integer , 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, with the search beginning at the start'th character of string. If N is omitted, it defaults to 1. See . regexp_replace('Thomas', '.', 'X', 3, 2) ThoXas regexp_replace(string=>'hello world', pattern=>'l', replacement=>'XX', start=>1, "N"=>2) helXXo world regexp_split_to_array regexp_split_to_array ( string text, pattern text , flags text ) text[] Splits string using a POSIX regular expression as the delimiter, producing an array of results; see . regexp_split_to_array('hello world', '\s+') {hello,world} regexp_split_to_table regexp_split_to_table ( string text, pattern text , flags text ) setof text Splits string using a POSIX regular expression as the delimiter, producing a set of results; see . regexp_split_to_table('hello world', '\s+') hello world regexp_substr regexp_substr ( string text, pattern text , start integer , N integer , flags text , 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 . regexp_substr('ABCDEF', 'c(.)(..)', 1, 1, 'i') CDEF regexp_substr('ABCDEF', 'c(.)(..)', 1, 1, 'i', 2) EF repeat repeat ( string text, number integer ) text Repeats string the specified number of times. repeat('Pg', 4) PgPgPgPg replace replace ( string text, from text, 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 ( string text, 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 split_part split_part ( string text, delimiter text, 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 ( string text, prefix text ) boolean Returns true if string starts with prefix. starts_with('alphabet', 'alph') t string_to_array string_to_array ( string text, delimiter text , 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 ( string text, delimiter text , 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 ( string text, 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 ( string text, start integer , 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 ( string text, encoding name ) text to_ascii ( string text, encoding integer ) text Converts string 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 module for another, more flexible solution.) to_ascii('Karél') Karel to_bin to_bin ( integer ) text to_bin ( bigint ) text Converts the number to its equivalent two's complement binary representation. to_bin(2147483647) 1111111111111111111111111111111 to_bin(-1234) 11111111111111111111101100101110 to_hex to_hex ( integer ) text to_hex ( bigint ) text Converts the number to its equivalent two's complement hexadecimal representation. to_hex(2147483647) 7fffffff to_hex(-1234) fffffb2e to_oct to_oct ( integer ) text to_oct ( bigint ) text Converts the number to its equivalent two's complement octal representation. to_oct(2147483647) 17777777777 to_oct(-1234) 37777775456 translate translate ( string text, from text, 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 ). unistr('d\0061t\+000061') data unistr('d\u0061t\U00000061') data 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 ). 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 , and the functions for converting between strings and the bytea type in . 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 %[position][flags][width]type 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, PostgreSQL'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 .