sql - How to perform coalesce on nullable columns

Question

I have three date columns which represented by strings.

Columns date1, and date2 are nullable columns. I want to order then in the following order - date1, date2, date3.

Is this a good workaround:

Select coalesce (NULLIF(date1,''), NULLIF(date2,''), date3)

Answer 1

如果您为丢失的日期存储 NULL 并且从不存储空白字符串，则 NullIF 是多余的，只需执行

Select coalesce (date1, date2, date3)