SQL使用空字符串进行合并

Question

我有以下内容：

     Select Coalesce(Other,Industry) Ind from registration

问题是其他可以是空字符串或NULL。 如何使coalesce工作，如果Other是一个空字符串，Coalesce仍然应该按照它应该运行？

Answer 1

使用CASE表达式或NULLIF：

SELECT COALESCE(NULLIF(Other,''),Industry) Ind FROM registration

Answer 2

试试这个

Select Coalesce(nullif(Other,''),Industry) Ind from registration

Answer 3

您也可以使用快捷方式，知道NULL <> ''未评估为TRUE ...

CASE WHEN other <> '' THEN other ELSE industry END

然后逻辑如下......

• CASE WHEN 'fubar' <> '' THEN other ELSE industry END
  =＆GT; CASE WHEN true THEN other ELSE industry END
  =＆GT; other

• CASE WHEN '' <> '' THEN other ELSE industry END
  =＆GT; CASE WHEN false THEN other ELSE industry END
  =＆GT; industry

• CASE WHEN NULL <> '' THEN other ELSE industry END
  =＆GT; CASE WHEN NULL THEN other ELSE industry END
  =＆GT; industry