[DRILL-162] Implement substring function

• Type: New Feature
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Fix Version/s: 0.1.0-m1
• Assignee: Ben Becker
• Reporter: Ben Becker
• Created: 04/Aug/13 07:29
• Updated: 09/Oct/13 18:09
• Resolved: 05/Aug/13 23:57

Description

Implement SUBSTRING with support for byte and character (UTF-8) sequences.

SUBSTRING ( expression , start, length )

Types:

expression: VARCHAR or VARBINARY
start: Literal BIGINT
length: Literal BIGINT
Returns: Same type as the expression argument

Arguments:

start: position within the expression value the return value will start from
length: number of subsequent characters or bytes to return.

Aliases:

SUBSTR
BYTE_SUBSTR

Return Value:

Returns the specified portion of the input string.

Notes on behavior:

• If the start position is negative, start from abs(start) characters from the end of the buffer.
• If no length is specified, continue to the end of the string.
• BYTE_SUBSTR always assumes a character is 8 bits, while SUBSTR accounts for UTF-8 character sequences.
• If the substring expression's length exceeds the value's upward bound, the
  value's length will be used.
• If the substring is invalid (e.g. negative length), return an empty string.