## 9.5. Binary String Functions and Operators

This section describes functions and operators for examining and manipulating values of type `bytea`.

SQL defines some string functions with a special syntax where certain key words rather than commas are used to separate the arguments. Details are in Table 9.8, “SQL Binary String Functions and Operators”. Some functions are also implemented using the regular syntax for function invocation. (See Table 9.9, “Other Binary String Functions”.)

Table 9.8. SQL Binary String Functions and Operators

Function | Return Type | Description | Example | Result
--- | --- | --- | --- | ---
``string` `||` `string`` | `bytea` | String concatenation | `'\\\\Post'::bytea || '\\047gres\\000'::bytea` | `\\Post'gres\000`
``octet_length`(`string`)` | `int` | Number of bytes in binary string | `octet_length( 'jo\\000se'::bytea)` | `5`
``position`(`substring` in `string`)` | `int` | Location of specified substring | `position('\\000om'::bytea in 'Th\\000omas'::bytea)` | `3`
``substring`(`string` [from `int`] [for `int`])` | `bytea` | Extract substring | `substring('Th\\000omas'::bytea from 2 for 3)` | `h\000o`
``trim`([both] `bytes` from `string`)` | `bytea` | Remove the longest string containing only the bytes in `bytes` from the start and end of `string` | `trim('\\000'::bytea from '\\000Tom\\000'::bytea)` | `Tom`
`get_byte`(`string`, `offset`) | `int` | Extract byte from string | `get_byte('Th\\000omas'::bytea, 4)` | `109`
`set_byte`(`string`, `offset`, `newvalue`) | `bytea` | Set byte in string | `set_byte('Th\\000omas'::bytea, 4, 64)` | `Th\000o@as`
`get_bit`(`string`, `offset`) | `int` | Extract bit from string | `get_bit('Th\\000omas'::bytea, 45)` | `1`
`set_bit`(`string`, `offset`, `newvalue`) | `bytea` | Set bit in string | `set_bit('Th\\000omas'::bytea, 45, 0)` | `Th\000omAs`

Additional binary string manipulation functions are available and are listed in Table 9.9, “Other Binary String Functions”. Some of them are used internally to implement the SQL-standard string functions listed in Table 9.8, “SQL Binary String Functions and Operators”.

Table 9.9. Other Binary String Functions

Function | Return Type | Description | Example | Result
--- | --- | --- | --- | ---
``btrim`(`string` `bytea`, `bytes` `bytea`)` | `bytea` | Remove the longest string consisting only of bytes in `bytes` from the start and end of `string` | `btrim('\\000trim\\000'::bytea, '\\000'::bytea)` | `trim`
``length`(`string`)` | `int` | Length of binary string | `length('jo\\000se'::bytea)` | `5`
``md5`(`string`)` | `text` | Calculates the MD5 hash of `string`, returning the result in hexadecimal | `md5('Th\\000omas'::bytea)` | `8ab2d3c9689aaf18 b4958c334c82d8b1`
``decode`(`string` `text`, `type` `text`)` | `bytea` | Decode binary string from `string` previously encoded with `encode`. Parameter type is same as in `encode`. | `decode('123\\000456', 'escape')` | `123\000456`
``encode`(`string` `bytea`, `type` `text`)` | `text` | Encode binary string to ASCII-only representation. Supported types are: `base64`, `hex`, `escape`. | `encode('123\\000456'::bytea, 'escape')` | `123\000456`