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Updated on 2022-08-16 GMT+08:00
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Binary String Functions and Operators

String operators

SQL defines some string functions that use keywords, rather than commas, to separate arguments.

  • octet_length(string)

    Description: Number of bytes in binary string

    Return type: int

    For example:

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    SELECT octet_length(E'jo\\000se'::bytea) AS RESULT;
 result
--------
      5
(1 row)
  • overlay(string placing string from int [for int])

    Description: Replaces substring.

    Return type: bytea

    For example:

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    SELECT overlay(E'Th\\000omas'::bytea placing E'\\002\\003'::bytea from 2 for 3) AS RESULT;
     result     
----------------
 \x5402036d6173
(1 row)
  • position(substring in string)

    Description: Location of specified substring

    Return type: int

    For example:

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    SELECT position(E'\\000om'::bytea in E'Th\\000omas'::bytea) AS RESULT;
 result
--------
      3
(1 row)
  • substring(string [from int] [for int])

    Description: Truncates substring.

    Return type: bytea

    For example:

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    SELECT substring(E'Th\\000omas'::bytea from 2 for 3) AS RESULT; 
  result  
----------
 \x68006f
(1 row)
  • trim([both] bytes from string)

    Description: Removes the longest string containing only bytes from bytes from the start and end of string.

    Return type: bytea

    For example:

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    SELECT trim(E'\\000'::bytea from E'\\000Tom\\000'::bytea) AS RESULT;
  result  
----------
 \x546f6d
(1 row)

Other Binary String Functions

GaussDB(DWS) also provides the common syntax used for invoking functions.

  • btrim(string bytea,bytes bytea)

    Description: Removes the longest string containing only bytes from bytes from the start and end of string.

    Return type: bytea

    For example:

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    SELECT btrim(E'\\000trim\\000'::bytea, E'\\000'::bytea) AS RESULT;
   result   
------------
 \x7472696d
(1 row)
  • get_bit(string, offset)

    Description: Extracts bit from string.

    Return type: int

    For example:

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    SELECT get_bit(E'Th\\000omas'::bytea, 45) AS RESULT; 
 result
--------
      1
(1 row)
  • get_byte(string, offset)

    Description: Extracts byte from string.

    Return type: int

    For example:

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    SELECT get_byte(E'Th\\000omas'::bytea, 4) AS RESULT; 
 result
--------
    109
(1 row)
  • set_bit(string,offset, newvalue)

    Description: Sets bit in string.

    Return type: bytea

    For example:

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    SELECT set_bit(E'Th\\000omas'::bytea, 45, 0) AS RESULT; 
      result      
------------------
 \x5468006f6d4173
(1 row)
  • set_byte(string,offset, newvalue)

    Description: Sets byte in string.

    Return type: bytea

    For example:

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    SELECT set_byte(E'Th\\000omas'::bytea, 4, 64) AS RESULT; 
      result      
------------------
 \x5468006f406173
(1 row)
Parent topic: Functions and Operators