SUBSTRING

Returns a substring.

Required arguments:

• Source string;
• Position: The offset from the beginning of the string in bytes (integer) or NULL meaning "from the beginning".

Optional arguments:

• Substring length: The number of bytes starting from the specified position (an integer, or the default NULL meaning "up to the end of the source string").

Indexing starts from zero. If the specified position and length are beyond the string, returns an empty string.
If the input string is optional, the result is also optional.

Examples

SELECT SUBSTRING("abcdefg", 3, 1); -- d

SELECT SUBSTRING("abcdefg", 3); -- defg

SELECT SUBSTRING("abcdefg", NULL, 3); -- abc