从MySQL数据库表中选择行时，如何使特定列值的第一行为空

注意：在从数据库表中选择行时，我希望将第一行TParent_Group_ID设置为零或空

BEGIN DECLARE done INT DEFAULT 0; DECLARE next_id INT; -- CURSOR TO LOOP THROUGH RESULTS -- DECLARE cur1 CURSOR FOR SELECT GID FROM civicsoft_group WHERE Parent_Group_ID = GivenID; DECLARE CONTINUE HANDLER FOR NOT FOUND SET done = 1; -- CREATE A TEMPORARY TABLE TO HOLD RESULTS -- IF initial=1 THEN -- MAKE SURE TABLE DOESN'T CONTAIN OUTDATED INFO IF IT EXISTS (USUALLY ON ERROR) -- DROP TABLE IF EXISTS OUT_TEMP; CREATE TEMPORARY TABLE OUT_TEMP (TGID int,TParent_Group_ID int, TGroup_Name varchar(32),TGroup_Type varchar(1),TProject_Status tinyint(1),TEID int,TEmp_Group_ID int,TEmp_Name varchar(100),TEmp_Type varchar(2)); END IF; -- ADD OURSELF TO THE TEMPORARY TABLE -- INSERT INTO OUT_TEMP SELECT cg.GID,cg.Parent_Group_ID,cg.Group_Name,cg.Group_Type,cg.Project_Status,ce.EID,ce.Emp_Group_ID,ce.Emp_Name,ce.Emp_Type FROM civicsoft_group cg LEFT JOIN civicsoft_employee ce ON cg.GID = ce.Emp_Group_ID WHERE cg.GID = GivenID; -- AND LOOP THROUGH THE CURSOR -- OPEN cur1; read_loop: LOOP FETCH cur1 INTO next_id; -- NO ROWS FOUND, LEAVE LOOP -- IF done THEN LEAVE read_loop; END IF; -- NEXT ROUND -- SET @@GLOBAL.max_sp_recursion_depth = 255; SET @@session.max_sp_recursion_depth = 255; CALL Hierarchy(next_id, 0); END LOOP; CLOSE cur1; -- THIS IS THE INITIAL CALL, LET'S GET THE RESULTS -- IF initial=1 THEN SELECT * FROM OUT_TEMP; -- Producing Final Temporary Table output -- CLEAN UP AFTER OURSELVES -- DROP TABLE OUT_TEMP; END IF; END

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创建特殊第一行的一般解决方案是：

select 0, null, null, ...
union all
select *
from ...
where ...

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第一行必须具有与第二行完全相同的数字和类型if列。您可以为第一行选择任何您喜欢的特殊值，只要编码的值与列类型兼容。

boss我是初学者，您能给我确切的解决方案吗？为什么您不能从这里应用解决方案。