[TAJO-746] Implements function COALESCE

• Type: New Feature
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Fix Version/s: 0.8.0
• Assignee: Hyoungjun Kim
• Reporter: Hyoungjun Kim
• Created: 09/Apr/14 09:36
• Updated: 12/May/14 08:30
• Resolved: 12/May/14 08:30

Description

See title.
The next description is from the postgresql document(http://www.postgresql.org/docs/9.1/static/functions-conditional.html).

COALESCE(value [, ...])

The COALESCE function returns the first of its arguments that is not null. Null is returned only if all arguments are null. It is often used to substitute a default value for null values when data is retrieved for display, for example:

SELECT COALESCE(description, short_description, '(none)') ...

Like a CASE expression, COALESCE only evaluates the arguments that are needed to determine the result; that is, arguments to the right of the first non-null argument are not evaluated. This SQL-standard function provides capabilities similar to NVL and IFNULL, which are used in some other database systems.