[英]MySql Toad if now rows return value
我正在使用mysql toad ,我有一個空的表,如果沒有找到記錄,我試圖返回一個字符串值。我嘗試了下面提到的查詢,但是沒有用,只返回一個空行。
詢問
select coalesce(stDate,'0')as StDate from tblStudents where studentNumber = 12213123;
select IFNULL(stDate,'0')as StDate from tblStudents where studentNumber = 12213123;
結果僅為空字符串,列stDate為varchar類型。
嘗試這個
select Cast(count(*) as char(10)) as StDate
from tblStudents where studentNumber = 12213123;
您還可以使用CASE語句,如果“學生編號”是唯一的,則max()或min()函數可從表中獲取stDate。
select Cast(count(*) as char(10)) as NumRows,max(stDate) as stDate
from tblStudents where studentNumber = 12213123;
如果您只想要一個字段,請嘗試這樣的操作
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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