Functions
The common functions of openGauss are as follows:
Mathematical Functions
abs(x)
Description: Absolute value
Return type: same as the input
Example:
""
openGauss=# SELECT abs(-17.4);
abs
17.4
(1 row)
cbrt(dp)
Description: Cubic root
Return type: double precision
Example:
""
openGauss=# SELECT cbrt(27.0);
cbrt
3
(1 row)
ceil(x)
Description: Minimum integer greater than or equal to the parameter
Return type: integer
Example:
""
openGauss=# SELECT ceil(-42.8);
ceil
-42
(1 row)
degrees(dp)
Description: Converts radians to angles.
Return type: double precision
Example:
""
openGauss=# SELECT degrees(0.5);
degrees
28.6478897565412
(1 row)
exp(x)
Description: Natural exponent
Return type: dp or numeric. If implicit type conversion is not considered, the return type is the same as the input type.
Example:
""
openGauss=# SELECT exp(1.0);
exp
2.7182818284590452
(1 row)
floor(x)
Description: Maximum integer not larger than the parameter
Return type: same as the input
Example:
""
openGauss=# SELECT floor(-42.8);
floor
-43
(1 row)
ln(x)
Description: Natural logarithm
Return type: dp or numeric. If implicit type conversion is not considered, the return type is the same as the input type.
Example:
""
openGauss=# SELECT ln(2.0);
ln
.6931471805599453
(1 row)
log(x)
Description: Logarithm with 10 as the base
Return type: same as the input
Example:
""
openGauss=# SELECT log(100.0);
log
2.0000000000000000
(1 row)
log(b numeric, x numeric)
Description: Logarithm with b as the base
Return type: numeric
Example:
""
openGauss=# SELECT log(2.0, 64.0);
log
6.0000000000000000
(1 row)
mod(x,y)
Description: Remainder of x/y (model) If x equals to 0, 0 is returned.
Return type: same as the parameter type
Example:
""
openGauss=# SELECT mod(9,4);
mod
1
(1 row)
""
openGauss=# SELECT mod(9,0);
mod
9
(1 row)
pi()
Description: π constant value
Return type: double precision
Example:
""
openGauss=# SELECT pi();
pi
3.14159265358979
(1 row)
power(a double precision, b double precision)
Description: b power of a
Return type: double precision
Example:
""
openGauss=# SELECT power(9.0, 3.0);
power
729.0000000000000000
(1 row)
radians(dp)
Description: Converts angles to radians.
Return type: double precision
Example:
""
openGauss=# SELECT radians(45.0);
radians
.785398163397448
(1 row)
random()
Description: Random number between 0.0 and 1.0
Return type: double precision
Example:
""
openGauss=# SELECT random();
random
.824823560658842
(1 row)
round(x)
Description: Integer closest to the input parameter
Return type: same as the input
Example:
""
openGauss=# SELECT round(42.4);
round
42
(1 row)
openGauss=# SELECT round(42.6);
round
43
(1 row)
round(v numeric, s int)
Description: s digits are kept after the decimal point.
Return type: numeric
Example:
""
openGauss=# SELECT round(42.4382, 2);
round
42.44
(1 row)
sign(x)
Description: Returns symbols of this parameter.
Return type: –1 indicates minus. 0 indicates 0, and 1 indicates positive numbers.
Example:
""
openGauss=# SELECT sign(-8.4);
sign
-1
(1 row)
sqrt(x)
Description: Square root
Return type: dp or numeric. If implicit type conversion is not considered, the return type is the same as the input type.
Example:
""
openGauss=# SELECT sqrt(2.0);
sqrt
1.414213562373095
(1 row)
trunc(x)
Description: Truncates (the integral part).
Return type: same as the input
Example:
""
openGauss=# SELECT trunc(42.8);
trunc
42
(1 row)
trunc(v numeric, s int)
Description: Truncates a number with s digits after the decimal point.
Return type: numeric
Example:
""
openGauss=# SELECT trunc(42.4382, 2);
trunc
42.43
(1 row)
Trigonometric Functions
acos(x)
Description: Arc cosine
Return type: double precision
Example:
""
openGauss=# SELECT acos(-1);
acos
3.14159265358979
(1 row)
asin(x)
Description: Arc sine
Return type: double precision
Example:
""
openGauss=# SELECT asin(0.5);
asin
.523598775598299
(1 row)
atan(x)
Description: Arc tangent
Return type: double precision
Example:
""
openGauss=# SELECT atan(1);
atan
.785398163397448
(1 row)
atan2(y, x)
Description: Arc tangent of y/x
Return type: double precision
Example:
""
openGauss=# SELECT atan2(2, 1);
atan2
1.10714871779409
(1 row)
cos(x)
Description: Cosine
Return type: double precision
Example:
""
openGauss=# SELECT cos(-3.1415927);
cos
-.999999999999999
(1 row)
cot(x)
Description: Cotangent
Return type: double precision
Example:
""
openGauss=# SELECT cot(1);
cot
.642092615934331
(1 row)
sin(x)
Description: Sine
Return type: double precision
Example:
""
openGauss=# SELECT sin(1.57079);
sin
.999999999979986
(1 row)
tan(x)
Description: Tangent
Return type: double precision
Example:
""
openGauss=# SELECT tan(20);
tan
2.23716094422474
(1 row)
String Functions and Operators
string || string
Description: Concatenates strings.
Return type: text
Example:
""
openGauss=# SELECT 'MPP'||'DB' AS RESULT;
result
MPPDB
(1 row)
bit_length(string)
Description: Specifies the number of bits occupied by a string.
Return type: int
Example:
""
openGauss=# SELECT bit_length('world');
bit_length
40
(1 row)
convert(string bytea, src_encoding name, dest_encoding name)
Description: Converts the bytea string to dest_encoding. src_encoding specifies the source code encoding. The string must be valid in this encoding.
Return type: bytea
Example:
""
openGauss=# SELECT convert('text_in_utf8', 'UTF8', 'GBK');
convert
\x746578745f696e5f75746638
(1 row)
lower(string)
Description: Converts the string into the lowercase.
Return type: varchar
Example:
""
openGauss=# SELECT lower('TOM');
lower
tom
(1 row)
octet_length(string)
Description: Specifies the number of bytes in a string.
Return type: int
Example:
""
openGauss=# SELECT octet_length('jose');
octet_length
4
(1 row)
overlay(string placing string FROM int [for int])
Description: Replaces substrings. FROM int indicates the start position of the replacement in the first string. for int indicates the number of characters replaced in the first string.
Return type: text
Example:
""
openGauss=# SELECT overlay('hello' placing 'world' from 2 for 3 );
overlay
hworldo
(1 row)
position(substring in string)
Description: Specifies the position of a substring. Parameters are case-sensitive.
Return type: int. If the character string does not exist, 0 is returned.
Example:
""
openGauss=# SELECT position('ing' in 'string');
position
4
(1 row)
substring(string [from int] [for int])
Description: Extracts a substring. from int indicates the start position of the truncation. for int indicates the number of characters truncated.
Return type: text
Example:
""
openGauss=# SELECT substring('Thomas' from 2 for 3);
substring
hom
(1 row)
substring(string from pattern)
Description: Extracts substrings matching the POSIX regular expression. It returns the text that matches the pattern. If no match record is found, a null value is returned.
Return type: text
Example:
""
openGauss=# SELECT substring('Thomas' from '...$');
substring
mas
(1 row)
openGauss=# SELECT substring('foobar' from 'o(.)b');
result
o
(1 row)
openGauss=# SELECT substring('foobar' from '(o(.)b)');
result
oob
(1 row)
trim([leading |trailing |both] [characters] from string)
Description: Removes the longest string containing only the characters (a space by default) from the start/end/both ends of the string.
Return type: varchar
Example:
""
openGauss=# SELECT trim(BOTH 'x' FROM 'xTomxx');
btrim
Tom
(1 row)
""
openGauss=# SELECT trim(LEADING 'x' FROM 'xTomxx');
ltrim
Tomxx
(1 row)
""
openGauss=# SELECT trim(TRAILING 'x' FROM 'xTomxx');
rtrim
xTom
(1 row)
upper(string)
Description: Converts the string into the uppercase.
Return type: varchar
Example:
""
openGauss=# SELECT upper('tom');
upper
TOM
(1 row)
ascii(string)
Description: Indicates the ASCII code of the first character in the string.
Return type: integer
Example:
""
openGauss=# SELECT ascii('xyz');
ascii
120
(1 row)
btrim(string text [, characters text])
Description: Removes the longest string consisting only of characters in characters (a space by default) from the start and end of string.
Return type: text
Example:
""
openGauss=# SELECT btrim('sring' , 'ing');
btrim
sr
(1 row)
chr(integer)
Description: Specifies the character of the ASCII code.
Return type: varchar
Example:
""
openGauss=# SELECT chr(65);
chr
A
(1 row)
convert(string bytea, src_encoding name, dest_encoding name)
Description: Converts the bytea string to dest_encoding. src_encoding specifies the source code encoding. The string must be valid in this encoding.
Return type: bytea
Example:
""
openGauss=# SELECT convert('text_in_utf8', 'UTF8', 'GBK');
convert
\x746578745f696e5f75746638
(1 row)
initcap(string)
Description: Converts the first letter of each word in the string into the uppercase and the other letters into the lowercase.
Return type: text
Example:
""
openGauss=# SELECT initcap('hi THOMAS');
initcap
Hi Thomas
(1 row)
length(string)
Description: Obtains the number of characters in a string.
Return type: integer
Example:
""
openGauss=# SELECT length('abcd');
length
4
(1 row)
lpad(string text, length int [, fill text])
Description: Fills up string to length by appending the characters fill (a space by default). If string is already longer than length, then it is truncated.
Return type: text
Example:
""
openGauss=# SELECT lpad('hi', 5, 'xyza');
lpad
xyzhi
(1 row)
ltrim(string [, characters])
Description: Removes the longest string containing only characters from characters (a space by default) from the start of string.
Return type: varchar
Example:
""
openGauss=# SELECT ltrim('xxxxTRIM','x');
ltrim
TRIM
(1 row)
md5(string)
Description: Encrypts a string in MD5 mode and returns a value in hexadecimal form.
NOTE: The MD5 encryption algorithm is not recommended because it has lower security and poses security risks.
Return type: text
Example:
""
openGauss=# SELECT md5('ABC');
md5
902fbdd2b1df0c4f70b4a5d23525e932
(1 row)
repeat(string text, number int )
Description: Repeats string the specified number of times.
Return type: text
Example:
""
openGauss=# SELECT repeat('Pg', 4);
repeat
PgPgPgPg
(1 row)
replace(string text, from text, to text)
Description: Replaces all occurrences in string of substring from with substring to.
Return type: text
Example:
""
openGauss=# SELECT replace('abcdefabcdef', 'cd', 'XXX');
replace
abXXXefabXXXef
(1 row)
rpad(string text, length int [, fill text])
Description: Fills up string to length by appending the characters fill (a space by default). If string is already longer than length, then it is truncated.
Return type: text
Example:
""
openGauss=# SELECT rpad('hi', 5, 'xy');
rpad
hixyx
(1 row)
rtrim(string text [, characters text])
Description: Removes the longest string containing only characters from characters (a space by default) from the end of string.
Return type: text
Example:
""
openGauss=# SELECT rtrim('trimxxxx', 'x');
rtrim
trim
(1 row)
split_part(string text, delimiter text, field int)
Description: Splits string on delimiter and returns the _field_th column (counting from text of the first appeared delimiter).
Return type: text
Example:
""
openGauss=# SELECT split_part('abc~@~def~@~ghi', '~@~', 2);
split_part
def
(1 row)
strpos(string, substring)
Description: Specifies the position of a substring. It is the same as position(substring in string). However, the parameter sequences of them are reversed.
Return type: int
Example:
""
openGauss=# SELECT strpos('source', 'rc');
strpos
4
(1 row)
to_hex(number int or bigint)
Description: Converts a number to a hexadecimal expression.
Return type: text
Example:
""
openGauss=# SELECT to_hex(2147483647);
to_hex
7fffffff
(1 row)
translate(string text, from text, to text)
Description: 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, extra characters occurred in from are removed.
Return type: text
Example:
""
openGauss=# SELECT translate('12345', '143', 'ax');
translate
a2x5
(1 row)
Functions Related to Type Conversion
to_char(timestamp, text)
Description: Converts the values of the timestamp type into the strings in the specified format.
Return type: text
Example:
""
openGauss=# SELECT to_char(current_timestamp, 'HH12:MI:SS');
to_char
10:55:59
(1 row)
to_char(interval, text)
Description: Converts the values of the time interval type into the strings in the specified format.
Return type: text
Example:
""
openGauss=# SELECT to_char(interval '15h 2m 12s', 'HH24:MI:SS');
to_char
15:02:12
(1 row)
to_char(int, text)
Description: Converts the values of the integer type into the strings in the specified format.
Return type: text
Example:
""
openGauss=# SELECT to_char(125, '999');
to_char
125
(1 row)
to_char(double precision/real, text)
Description: Converts the values of the floating point type into the strings in the specified format.
Return type: text
Example:
""
openGauss=# SELECT to_char(125.8::real, '999D99');
to_char
125.80
(1 row)
to_char(numeric, text)
Description: Converts the values of the numeric type into the strings in the specified format.
Return type: text
Example:
""
openGauss=# SELECT to_char(-125.8, '999D99S');
to_char
125.80-
(1 row)
to_date(text, text)
Description: Converts the values of the string type into the dates in the specified format.
Return type: timestamp without time zone
Example:
""
openGauss=# SELECT to_date('05 Dec 2000', 'DD Mon YYYY');
to_date
2000-12-05 00:00:00
(1 row)
to_number(text, text)
Description: Converts the values of the string type into the numbers in the specified format.
Return type: numeric
Example:
""
openGauss=# SELECT to_number('12,454.8-', '99G999D9S');
to_number
-12454.8
(1 row)
to_timestamp(text, text)
Description: Converts values of the string type into the timestamp of the specified type.
Return type: timestamp
Example:
""
openGauss=# SELECT to_timestamp('05 Dec 2000', 'DD Mon YYYY');
to_timestamp
2000-12-05 00:00:00
(1 row)
to_timestamp(double precision)
Description: Converts a UNIX century into a timestamp.
Return type: timestamp with time zone
Example:
""
openGauss=# SELECT to_timestamp(1284352323);
to_timestamp
2010-09-13 12:32:03+08
(1 row)
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