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cowellce工作,如果Other是一个空字符串,Coalesce仍然应该按照它应该的行为？

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

您还可以使用NULL <> ''不评估为TRUE...的快捷方式

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

然后逻辑如下......

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

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

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