postgresql coalesce COALESCE

版权声明：本文为博主原创文章，未经博主允许不得转载。 https://blog.csdn.net/u011944141/article/details/82317069

https://www.postgresql.org/docs/10/static/functions-conditional.html#FUNCTIONS-COALESCE

9.17.2. COALESCE

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)') ...

This returns description if it is not null, otherwise short_description if it is not null, otherwise (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.

explame:

select coalesce(null, 'test');
 coalesce 
----------
 test
(1 row)

select coalesce(null, 0);
 coalesce 
----------
        0
(1 row)