hyoungjunkim created TAJO-746:
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Summary: Implements function COALESCE
Key: TAJO-746
URL: https://issues.apache.org/jira/browse/TAJO-746
Project: Tajo
Issue Type: New Feature
Reporter: hyoungjunkim
See title.
The next description is from the postgresql
document(http://www.postgresql.org/docs/9.1/static/functions-conditional.html).
{noformat}
COALESCE(value [, ...])
{noformat}
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:
{code:sql}
SELECT COALESCE(description, short_description, '(none)') ...
{code}
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.
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