[英]MySql Toad if now rows return value
我正在使用mysql toad ,我有一个空的表,如果没有找到记录,我试图返回一个字符串值。我尝试了下面提到的查询,但是没有用,只返回一个空行。
询问
select coalesce(stDate,'0')as StDate from tblStudents where studentNumber = 12213123;
select IFNULL(stDate,'0')as StDate from tblStudents where studentNumber = 12213123;
结果仅为空字符串,列stDate为varchar类型。
尝试这个
select Cast(count(*) as char(10)) as StDate
from tblStudents where studentNumber = 12213123;
您还可以使用CASE语句,如果“学生编号”是唯一的,则max()或min()函数可从表中获取stDate。
select Cast(count(*) as char(10)) as NumRows,max(stDate) as stDate
from tblStudents where studentNumber = 12213123;
如果您只想要一个字段,请尝试这样的操作
select
CASE count(*)
WHEN 0 THEN ''
ELSE CAST(max(stDate) as char(12))
END CASE as StartDate
from tblStudents where studentNumber = 12213123;
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