Oracle空检查字符串字段 [英] Oracle null check for string field

问题描述

在下面的示例中，为什么在Oracle 11g中除"NAME1"以外的所有结果都为空.

In this below example why other than "NAME1" all giving null as result in oracle 11g.

如果我明确提到空格，则需要空格，否则仅返回null而不是空字符串.请帮助我阐明这一点.

If I mention space explicitly it takes space otherwise null only not empty string.Please help me to clarify this.

在NAME2中，我指定了空白，但仍然为null.

In NAME2 I specify the empty space but still it gives null.

select 
NVL(NAME,' ') AS NAME1,
NVL(NAME,'') AS NAME2,
NVL(NAME,NULL) AS NAME3,
NAME AS NAME4 
from employee

输出:

(空格)，null，null，null

(space),null,null,null

推荐答案

在Oracle中，零长度的varchar被视为NULL.

Because in Oracle a ZERO length varchar is treated as NULL.

在您的示例中

NVL(NAME, ' ') AS NAME1 will evaluate to either NAME or ' ' - empty string.
NVL(NAME, '') as NAME2 will evaluate to either NAME or a zero length string

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