SQL 从 PostgreSQL 中选择日期（时间戳）作为字符串（字符），注意 NULL 值
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Select date (timestamp) from PostgreSQL as string (char), beware of NULL value
提问by Katie
I want to select a date (my column is a timestamp type). But when in column is a NULL date, I want to return an empty string. How to do this? I wrote this:
我想选择一个日期（我的列是时间戳类型）。但是当列是一个空日期时，我想返回一个空字符串。这该怎么做？我是这样写的：
SELECT
CASE WHEN to_char(last_post, 'MM-DD-YYYY HH24:MI:SS') IS NULL THEN ''
ELSE to_char(last_post, 'MM-DD-YYYY HH24:MI:SS') AS last_post END
to_char(last_post, 'MM-DD-YYYY HH24:MI:SS') AS last_post, content
FROM topic;
But it shows me some errors, dont really know why:
但它显示了一些错误，不知道为什么：
ERROR: syntax error at or near "as"
LINE 1: ...ELSE to_char(last_post, 'MM-DD-YYYY HH24:MI:SS') AS last_po...
^
回答by Nerdwood
Using the COALESCE()function is the nicest approach, as it simply swaps in a substitute value in the case of a NULL. Readability is improved greatly too. :)
使用该COALESCE()函数是最好的方法，因为它只是在 NULL 的情况下交换一个替代值。可读性也大大提高。:)
SELECT COALESCE(to_char(last_post, 'MM-DD-YYYY HH24:MI:SS'), '') AS last_post, content FROM topic;
回答by Jerry
You're putting your ASwithin the case?
你把你的AS放在案子里？
Try:
尝试：
SELECT
CASE WHEN last_post IS NULL THEN ''
ELSE to_char(last_post, 'MM-DD-YYYY HH24:MI:SS') END AS last_post,
content
FROM topic;
I haven't tried the query though.
我还没有尝试过查询。
回答by Clodoaldo Neto
select coalesce(to_char(last_post, 'MM-DD-YYYY HH24:MI:SS'), '') as last_post, content
from topic;
