ifnull是postgresql自带的function吗？

[lord_is_layuping]

ifnull是postgresql自带的function吗？

报错如下：

function ifnull(timestamp without time zone, character varying) does not exist

[ACMAIN_CHM]

不是PostgreSQL 自带的函数， PostgreSQL 中相同功能的函数是 COALESCE

[ACMAIN_CHM]

[Quote=PostgreSQL 8.4.0 Documentation
]9.16.2. 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)') ...
[/Quote]

[lord_is_layuping]

嗯嗯，非常感谢，ls，postgresql中有像下面这个DateDiff对应的函数吗？
DATEDIFF(date1,date2)

date1 和 date2 参数是合法的日期或日期/时间表达式。

[ACMAIN_CHM]

直接减就行了。
date2 - date1

结果就是天。

[wwwwb]

POSTGRESQL没有IFNULL函数，有
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)') ...
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.

没有DateDiff对应的函数，直接相减
date '2001-10-01' - date '2001-09-28' integer '3' (days)