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)
```

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)
```

Functions

Mathematical Functions

Trigonometric Functions

String Functions and Operators

Functions Related to Type Conversion