Oracle：如果字段为空则显示特殊文本
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Oracle: Show special text if field is null
提问by Svish
I would like to write a select where I show the value of the field as normal except when the field is null. If it is null I'd like to show a special text, for example "Field is null". How would I best do this?
我想写一个选择，在那里我正常显示字段的值，除非该字段为空。如果它为空，我想显示一个特殊的文本，例如“字段为空”。我怎么做最好？
// Oracle newbie
回答by Tommi
I like to use function COALESCEfor this purpose. It returns the first non-null value from given arguments (so you can test more than one field at a time).
我喜欢COALESCE为此目的使用函数。它从给定的参数返回第一个非空值（因此您可以一次测试多个字段）。
SELECT COALESCE(NULL, 'Special text') FROM DUAL
So this would also work:
所以这也可以：
SELECT COALESCE(
First_Nullable_Field,
Second_Nullable_Field,
Third_Nullable_Field,
'All fields are NULL'
) FROM YourTable
回答by Pepto
Just insert the NVL PL/SQL function into your query
只需将 NVL PL/SQL 函数插入您的查询中
SELECT NVL(SOMENULLABLEFIELD,'Field Is Null') SOMENULLABLEFIELD FROM MYTABLE;
从 MYTABLE 中选择 NVL(SOMENULLABLEFIELD,'Field Is Null') SOMENULLABLEFIELD;
More detail here : http://www.techonthenet.com/oracle/functions/nvl.php
更多细节在这里：http: //www.techonthenet.com/oracle/functions/nvl.php
回答by Frank Schmitt
You could also use DECODE:
您还可以使用解码：
select value, decode(value, NULL, 'SPECIAL', value) from
(select NULL value from dual
union all
select 2 value from dual
)
