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
. Unless otherwise noted, all
of the functions listed below work on all of these types, but be
wary of potential effects of automatic space-padding when using the
character
type. Some functions also exist
natively for the bit-string types.
SQL defines some string functions that use key words, rather than commas, to separate arguments. Details are in Table 9.8. PostgreSQL also provides versions of these functions that use the regular function invocation syntax (see Table 9.9).
Before PostgreSQL 8.3, these functions would
silently accept values of several non-string data types as well, due to
the presence of implicit coercions from those data types to
text
. Those coercions have been removed because they frequently
caused surprising behaviors. However, the string concatenation operator
(||
) still accepts non-string input, so long as at least one
input is of a string type, as shown in Table 9.8. For other cases, insert an explicit
coercion to text
if you need to duplicate the previous behavior.
Table 9.8. SQL String Functions and Operators
Function | Return Type | Description | Example | Result |
---|---|---|---|---|
| text | String concatenation | 'Post' || 'greSQL' | PostgreSQL |
or
| text | String concatenation with one non-string input | 'Value: ' || 42 | Value: 42 |
| int | Number of bits in string | bit_length('jose') | 32 |
or
| int | Number of characters in string | char_length('jose') | 4 |
| text | Convert string to lower case | lower('TOM') | tom |
| int | Number of bytes in string | octet_length('jose') | 4 |
| text | Replace substring | overlay('Txxxxas' placing 'hom' from 2 for 4) | Thomas |
| int | Location of specified substring | position('om' in 'Thomas') | 3 |
| text | Extract substring | substring('Thomas' from 2 for 3) | hom |
| text | Extract substring matching POSIX regular expression. See Section 9.7 for more information on pattern matching. | substring('Thomas' from '...$') | mas |
| text | Extract substring matching SQL regular expression. See Section 9.7 for more information on pattern matching. | substring('Thomas' from '%#"o_a#"_' for '#') | oma |
| text | Remove the longest string containing only characters from
characters (a space by default) from the
start, end, or both ends (both is the default)
of string
| trim(both 'xyz' from 'yxTomxx') | Tom |
| text | Non-standard syntax for trim()
| trim(both from 'yxTomxx', 'xyz') | Tom |
| text | Convert string to upper case | upper('tom') | TOM |
Additional string manipulation functions are available and are listed in Table 9.9. Some of them are used internally to implement the SQL-standard string functions listed in Table 9.8.
Table 9.9. Other String Functions
Function | Return Type | Description | Example | Result |
---|---|---|---|---|
| int | ASCII code of the first character of the argument. For UTF8 returns the Unicode code point of the character. For other multibyte encodings, the argument must be an ASCII character. | ascii('x') | 120 |
| text | Remove the longest string consisting only of characters
in characters (a space by default)
from the start and end of string
| btrim('xyxtrimyyx', 'xyz') | trim |
| text | Character with the given code. For UTF8 the argument is treated as a Unicode code point. For other multibyte encodings the argument must designate an ASCII character. The NULL (0) character is not allowed because text data types cannot store such bytes. | chr(65) | A |
| text | Concatenate the text representations of all the arguments. NULL arguments are ignored. | concat('abcde', 2, NULL, 22) | abcde222 |
| text | Concatenate all but the first argument with separators. The first argument is used as the separator string. NULL arguments are ignored. | concat_ws(',', 'abcde', 2, NULL, 22) | abcde,2,22 |
| bytea | Convert string to dest_encoding . The
original encoding is specified by
src_encoding . The
string must be valid in this encoding.
Conversions can be defined by CREATE CONVERSION .
Also there are some predefined conversions. See Table 9.10 for available conversions.
| convert('text_in_utf8', 'UTF8', 'LATIN1') | text_in_utf8 represented in Latin-1
encoding (ISO 8859-1) |
| text | Convert string to the database encoding. The original encoding
is specified by src_encoding . The
string must be valid in this encoding.
| convert_from('text_in_utf8', 'UTF8') | text_in_utf8 represented in the current database encoding |
| bytea | Convert string to dest_encoding .
| convert_to('some text', 'UTF8') | some text represented in the UTF8 encoding |
| bytea | Decode binary data from textual representation in string .
Options for format are same as in encode .
| decode('MTIzAAE=', 'base64') | \x3132330001 |
| text | Encode binary data into a textual representation. Supported
formats are: base64 , hex , escape .
escape converts zero bytes and high-bit-set bytes to
octal sequences (\ nnn ) and
doubles backslashes.
| encode(E'123\\000\\001', 'base64') | MTIzAAE= |
| text | Format arguments according to a format string.
This function is similar to the C function sprintf .
See Section 9.4.1.
| format('Hello %s, %1$s', 'World') | Hello World, World |
| text | Convert 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 |
| text | Return first n characters in the string. When n
is negative, return all but last |n | characters.
| left('abcde', 2) | ab |
| int | Number of characters in string
| length('jose') | 4 |
| int | Number of characters in string in the given
encoding . The string
must be valid in this encoding.
| length('jose', 'UTF8') | 4 |
| text | Fill up 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 |
| text | Remove the longest string containing only characters from
characters (a space by default) from the start of
string
| ltrim('zzzytest', 'xyz') | test |
| text | Calculates the MD5 hash of string ,
returning the result in hexadecimal
| md5('abc') | 900150983cd24fb0 d6963f7d28e17f72 |
| text[] | Split 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} |
| name | Current client encoding name | pg_client_encoding() | SQL_ASCII |
| text | Return 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 42.1. | quote_ident('Foo bar') | "Foo bar" |
| text | Return 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 42.1.
| quote_literal(E'O\'Reilly') | 'O''Reilly' |
| text | Coerce the given value to text and then quote it as a literal. Embedded single-quotes and backslashes are properly doubled. | quote_literal(42.5) | '42.5' |
| text | Return the given string suitably quoted to be used as a string literal
in an SQL statement string; or, if the argument
is null, return NULL .
Embedded single-quotes and backslashes are properly doubled.
See also Example 42.1.
| quote_nullable(NULL) | NULL |
| text | Coerce the given value to text and then quote it as a literal;
or, if the argument is null, return NULL .
Embedded single-quotes and backslashes are properly doubled.
| quote_nullable(42.5) | '42.5' |
| text[] | Return captured substring(s) resulting from the first match of a POSIX
regular expression to the string . See
Section 9.7.3 for more information.
| regexp_match('foobarbequebaz', '(bar)(beque)') | {bar,beque} |
| setof text[] | Return captured substring(s) resulting from matching a POSIX regular
expression to the string . See
Section 9.7.3 for more information.
| regexp_matches('foobarbequebaz', 'ba.', 'g') | {bar}
|
| text | Replace substring(s) matching a POSIX regular expression. See Section 9.7.3 for more information. | regexp_replace('Thomas', '.[mN]a.', 'M') | ThM |
| text[] | Split string using a POSIX regular expression as
the delimiter. See Section 9.7.3 for more
information.
| regexp_split_to_array('hello world', E'\\s+') | {hello,world} |
| setof text | Split string using a POSIX regular expression as
the delimiter. See Section 9.7.3 for more
information.
| regexp_split_to_table('hello world', E'\\s+') | hello
|
| text | Repeat string the specified
number of times | repeat('Pg', 4) | PgPgPgPg |
| text | Replace all occurrences in string of substring
from with substring to
| replace('abcdefabcdef', 'cd', 'XX') | abXXefabXXef |
| text | Return reversed string. | reverse('abcde') | edcba |
| text | Return last n characters in the string. When n
is negative, return all but first |n | characters.
| right('abcde', 2) | de |
| text | Fill up 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 |
| text | Remove the longest string containing only characters from
characters (a space by default) from the end of
string
| rtrim('testxxzx', 'xyz') | test |
| text | Split string on delimiter
and return the given field (counting from one)
| split_part('abc~@~def~@~ghi', '~@~', 2) | def |
| int | Location of specified substring (same as
position( , but note the reversed
argument order)
| strpos('high', 'ig') | 2 |
| text | Extract substring (same as
substring( )
| substr('alphabet', 3, 2) | ph |
| text | Convert string to ASCII from another encoding
(only supports conversion from LATIN1 , LATIN2 , LATIN9 ,
and WIN1250 encodings)
| to_ascii('Karel') | Karel |
| text | Convert number to its equivalent hexadecimal
representation
| to_hex(2147483647) | 7fffffff |
| text | Any character in string that matches a
character in the from set is replaced by
the corresponding character in the to
set. If from is longer than
to , occurrences of the extra characters in
from are removed.
| translate('12345', '143', 'ax') | a2x5 |
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 37.4.5). 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 9.20.
Table 9.10. Built-in Conversions
Conversion Name [a] | Source Encoding | Destination Encoding |
---|---|---|
ascii_to_mic | SQL_ASCII | MULE_INTERNAL |
ascii_to_utf8 | SQL_ASCII | UTF8 |
big5_to_euc_tw | BIG5 | EUC_TW |
big5_to_mic | BIG5 | MULE_INTERNAL |
big5_to_utf8 | BIG5 | UTF8 |
euc_cn_to_mic | EUC_CN | MULE_INTERNAL |
euc_cn_to_utf8 | EUC_CN | UTF8 |
euc_jp_to_mic | EUC_JP | MULE_INTERNAL |
euc_jp_to_sjis | EUC_JP | SJIS |
euc_jp_to_utf8 | EUC_JP | UTF8 |
euc_kr_to_mic | EUC_KR | MULE_INTERNAL |
euc_kr_to_utf8 | EUC_KR | UTF8 |
euc_tw_to_big5 | EUC_TW | BIG5 |
euc_tw_to_mic | EUC_TW | MULE_INTERNAL |
euc_tw_to_utf8 | EUC_TW | UTF8 |
gb18030_to_utf8 | GB18030 | UTF8 |
gbk_to_utf8 | GBK | UTF8 |
iso_8859_10_to_utf8 | LATIN6 | UTF8 |
iso_8859_13_to_utf8 | LATIN7 | UTF8 |
iso_8859_14_to_utf8 | LATIN8 | UTF8 |
iso_8859_15_to_utf8 | LATIN9 | UTF8 |
iso_8859_16_to_utf8 | LATIN10 | UTF8 |
iso_8859_1_to_mic | LATIN1 | MULE_INTERNAL |
iso_8859_1_to_utf8 | LATIN1 | UTF8 |
iso_8859_2_to_mic | LATIN2 | MULE_INTERNAL |
iso_8859_2_to_utf8 | LATIN2 | UTF8 |
iso_8859_2_to_windows_1250 | LATIN2 | WIN1250 |
iso_8859_3_to_mic | LATIN3 | MULE_INTERNAL |
iso_8859_3_to_utf8 | LATIN3 | UTF8 |
iso_8859_4_to_mic | LATIN4 | MULE_INTERNAL |
iso_8859_4_to_utf8 | LATIN4 | UTF8 |
iso_8859_5_to_koi8_r | ISO_8859_5 | KOI8R |
iso_8859_5_to_mic | ISO_8859_5 | MULE_INTERNAL |
iso_8859_5_to_utf8 | ISO_8859_5 | UTF8 |
iso_8859_5_to_windows_1251 | ISO_8859_5 | WIN1251 |
iso_8859_5_to_windows_866 | ISO_8859_5 | WIN866 |
iso_8859_6_to_utf8 | ISO_8859_6 | UTF8 |
iso_8859_7_to_utf8 | ISO_8859_7 | UTF8 |
iso_8859_8_to_utf8 | ISO_8859_8 | UTF8 |
iso_8859_9_to_utf8 | LATIN5 | UTF8 |
johab_to_utf8 | JOHAB | UTF8 |
koi8_r_to_iso_8859_5 | KOI8R | ISO_8859_5 |
koi8_r_to_mic | KOI8R | MULE_INTERNAL |
koi8_r_to_utf8 | KOI8R | UTF8 |
koi8_r_to_windows_1251 | KOI8R | WIN1251 |
koi8_r_to_windows_866 | KOI8R | WIN866 |
koi8_u_to_utf8 | KOI8U | UTF8 |
mic_to_ascii | MULE_INTERNAL | SQL_ASCII |
mic_to_big5 | MULE_INTERNAL | BIG5 |
mic_to_euc_cn | MULE_INTERNAL | EUC_CN |
mic_to_euc_jp | MULE_INTERNAL | EUC_JP |
mic_to_euc_kr | MULE_INTERNAL | EUC_KR |
mic_to_euc_tw | MULE_INTERNAL | EUC_TW |
mic_to_iso_8859_1 | MULE_INTERNAL | LATIN1 |
mic_to_iso_8859_2 | MULE_INTERNAL | LATIN2 |
mic_to_iso_8859_3 | MULE_INTERNAL | LATIN3 |
mic_to_iso_8859_4 | MULE_INTERNAL | LATIN4 |
mic_to_iso_8859_5 | MULE_INTERNAL | ISO_8859_5 |
mic_to_koi8_r | MULE_INTERNAL | KOI8R |
mic_to_sjis | MULE_INTERNAL | SJIS |
mic_to_windows_1250 | MULE_INTERNAL | WIN1250 |
mic_to_windows_1251 | MULE_INTERNAL | WIN1251 |
mic_to_windows_866 | MULE_INTERNAL | WIN866 |
sjis_to_euc_jp | SJIS | EUC_JP |
sjis_to_mic | SJIS | MULE_INTERNAL |
sjis_to_utf8 | SJIS | UTF8 |
tcvn_to_utf8 | WIN1258 | UTF8 |
uhc_to_utf8 | UHC | UTF8 |
utf8_to_ascii | UTF8 | SQL_ASCII |
utf8_to_big5 | UTF8 | BIG5 |
utf8_to_euc_cn | UTF8 | EUC_CN |
utf8_to_euc_jp | UTF8 | EUC_JP |
utf8_to_euc_kr | UTF8 | EUC_KR |
utf8_to_euc_tw | UTF8 | EUC_TW |
utf8_to_gb18030 | UTF8 | GB18030 |
utf8_to_gbk | UTF8 | GBK |
utf8_to_iso_8859_1 | UTF8 | LATIN1 |
utf8_to_iso_8859_10 | UTF8 | LATIN6 |
utf8_to_iso_8859_13 | UTF8 | LATIN7 |
utf8_to_iso_8859_14 | UTF8 | LATIN8 |
utf8_to_iso_8859_15 | UTF8 | LATIN9 |
utf8_to_iso_8859_16 | UTF8 | LATIN10 |
utf8_to_iso_8859_2 | UTF8 | LATIN2 |
utf8_to_iso_8859_3 | UTF8 | LATIN3 |
utf8_to_iso_8859_4 | UTF8 | LATIN4 |
utf8_to_iso_8859_5 | UTF8 | ISO_8859_5 |
utf8_to_iso_8859_6 | UTF8 | ISO_8859_6 |
utf8_to_iso_8859_7 | UTF8 | ISO_8859_7 |
utf8_to_iso_8859_8 | UTF8 | ISO_8859_8 |
utf8_to_iso_8859_9 | UTF8 | LATIN5 |
utf8_to_johab | UTF8 | JOHAB |
utf8_to_koi8_r | UTF8 | KOI8R |
utf8_to_koi8_u | UTF8 | KOI8U |
utf8_to_sjis | UTF8 | SJIS |
utf8_to_tcvn | UTF8 | WIN1258 |
utf8_to_uhc | UTF8 | UHC |
utf8_to_windows_1250 | UTF8 | WIN1250 |
utf8_to_windows_1251 | UTF8 | WIN1251 |
utf8_to_windows_1252 | UTF8 | WIN1252 |
utf8_to_windows_1253 | UTF8 | WIN1253 |
utf8_to_windows_1254 | UTF8 | WIN1254 |
utf8_to_windows_1255 | UTF8 | WIN1255 |
utf8_to_windows_1256 | UTF8 | WIN1256 |
utf8_to_windows_1257 | UTF8 | WIN1257 |
utf8_to_windows_866 | UTF8 | WIN866 |
utf8_to_windows_874 | UTF8 | WIN874 |
windows_1250_to_iso_8859_2 | WIN1250 | LATIN2 |
windows_1250_to_mic | WIN1250 | MULE_INTERNAL |
windows_1250_to_utf8 | WIN1250 | UTF8 |
windows_1251_to_iso_8859_5 | WIN1251 | ISO_8859_5 |
windows_1251_to_koi8_r | WIN1251 | KOI8R |
windows_1251_to_mic | WIN1251 | MULE_INTERNAL |
windows_1251_to_utf8 | WIN1251 | UTF8 |
windows_1251_to_windows_866 | WIN1251 | WIN866 |
windows_1252_to_utf8 | WIN1252 | UTF8 |
windows_1256_to_utf8 | WIN1256 | UTF8 |
windows_866_to_iso_8859_5 | WIN866 | ISO_8859_5 |
windows_866_to_koi8_r | WIN866 | KOI8R |
windows_866_to_mic | WIN866 | MULE_INTERNAL |
windows_866_to_utf8 | WIN866 | UTF8 |
windows_866_to_windows_1251 | WIN866 | WIN |
windows_874_to_utf8 | WIN874 | UTF8 |
euc_jis_2004_to_utf8 | EUC_JIS_2004 | UTF8 |
utf8_to_euc_jis_2004 | UTF8 | EUC_JIS_2004 |
shift_jis_2004_to_utf8 | SHIFT_JIS_2004 | UTF8 |
utf8_to_shift_jis_2004 | UTF8 | SHIFT_JIS_2004 |
euc_jis_2004_to_shift_jis_2004 | EUC_JIS_2004 | SHIFT_JIS_2004 |
shift_jis_2004_to_euc_jis_2004 | SHIFT_JIS_2004 | EUC_JIS_2004 |
[a] The conversion names follow a standard naming scheme: The
official name of the source encoding with all
non-alphanumeric characters replaced by underscores, followed
by |
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
where
n
$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 *
to
use the n
$n
th function argument as the width.
If the width comes from a function argument, that argument is
consumed before the argument that is used for the format specifier's
value. If the width argument is negative, the result is left
aligned (as if the -
flag had been specified) within a
field of length abs
(width
).
type
(required)The type of format conversion to use to produce the format specifier's output. The following types are supported:
s
formats the argument value as a simple
string. A null value is treated as an empty string.
I
treats the argument value as an SQL
identifier, double-quoting it if necessary.
It is an error for the value to be null (equivalent to
quote_ident
).
L
quotes the argument value as an SQL literal.
A null value is displayed as the string NULL
, without
quotes (equivalent to quote_nullable
).
In addition to the format specifiers described above, the special sequence
%%
may be used to output a literal %
character.
Here are some examples of the basic format conversions:
SELECT format('Hello %s', 'World'); Result:Hello World
SELECT format('Testing %s, %s, %s, %%', 'one', 'two', 'three'); Result:Testing one, two, three, %
SELECT format('INSERT INTO %I VALUES(%L)', 'Foo bar', E'O\'Reilly'); Result:INSERT INTO "Foo bar" VALUES('O''Reilly')
SELECT format('INSERT INTO %I VALUES(%L)', 'locations', E'C:\\Program Files'); Result:INSERT INTO locations VALUES(E'C:\\Program Files')
Here are examples using width
fields
and the -
flag:
SELECT format('|%10s|', 'foo'); Result:| foo|
SELECT format('|%-10s|', 'foo'); Result:|foo |
SELECT format('|%*s|', 10, 'foo'); Result:| foo|
SELECT format('|%*s|', -10, 'foo'); Result:|foo |
SELECT format('|%-*s|', 10, 'foo'); Result:|foo |
SELECT format('|%-*s|', -10, 'foo'); Result:|foo |
These examples show use of position
fields:
SELECT format('Testing %3$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
Example 42.1.