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:

postgres=# 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:

postgres=# 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:

postgres=# 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:

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

Other Binary String Functions

openGauss provides common syntax used for calling 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:
```
postgres=# 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:

postgres=# 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:

postgres=# 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:

postgres=# 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:

postgres=# SELECT set_byte(E'Th\\000omas'::bytea, 4, 64) AS RESULT; 
      result      
------------------
 \x5468006f406173
(1 row)