Returns a byte sequence from a given sequence of octets (8-bit bytes).
The format for the $ZEXTRACT function is:
$ZE[XTRACT](expr[,intexpr1[,intexpr2]])
The expression specifies a sequence of octets (8-bit bytes) from which $ZEXTRACT() derives a byte sequence.
The first optional integer expression (second argument) specifies the starting byte position in the byte string. If the starting position is beyond the end of the expression, $ZEXTRACT() returns an empty string. If the starting position is zero (0) or negative, $ZEXTRACT() starts at the first byte position in the expression; if this argument is omitted, $ZEXTRACT() returns the first byte. $ZEXTRACT() numbers byte positions starting at one (1) (the first byte of a sequence of octets (8-bit bytes) is at position one (1)).
The second optional integer expression (third argument) specifies the ending byte position for the result. If the ending position is beyond the end of the expression, $ZEXTRACT() stops with the last byte of the expression. If the ending position precedes the starting position, $ZEXTRACT() returns null. If this argument is omitted, $ZEXTRACT() returns one byte.
$ZEXTRACT() provides a tool for manipulating strings based on byte positions.
As $ZEXTRACT() operates on bytes, it can produce a string that is not well-formed according to the UTF-8 character set.
