Returns a substring of a string. The substring is calculated using bytes, not characters.
BYTE_SUBSTR( string-expression, start [, length ] )
string-expression The string from which the substring is taken.
start An integer expression indicating the start of the substring. A positive integer starts from the beginning of the string, with the first character being position 1. A negative integer specifies a substring starting from the end of the string, the final character being at position -1.
length An integer expression indicating the length of the substring. A positive length specifies the number of bytes to be taken starting at the start position. A negative length returns at most length bytes up to, and including, the starting position, from the left of the starting position.
If length is specified, the substring is restricted to that number of bytes. Both start and length can be either positive or negative. Using appropriate combinations of negative and positive numbers, you can get a substring from either the beginning or end of the string.
If start is zero and length is non-negative, a start value of 1 is used. If start is zero and length is negative, a start value of -1 is used.
SQL/2003 Vendor extension.
The following statement returns the value Test.
SELECT BYTE_SUBSTR( 'Test Message', 1, 4 );