[英]Select records from a table based on column value from same table
I have already written the following query.我已经编写了以下查询。
DECLARE @LEVEL NVARCHAR(10), @ID INT = 12 SELECT @LEVEL = RTRIM(LEVEL_NEW) FROM HIER WHERE ID = @ID IF (@LEVEL = 'LEVEL 1') SELECT * FROM HIER WHERE FC_LEVEL1 = @ID ELSE IF (@LEVEL = 'LEVEL 2') SELECT * FROM HIER WHERE FC_LEVEL2 = @ID ELSE IF (@LEVEL = 'LEVEL 3') SELECT * FROM HIER WHERE FC_LEVEL3 = @ID
The above query works well.上面的查询运行良好。 But I would like to have a single query with join and case expression.
但我想要一个带有连接和 case 表达式的查询。 Any help would be highly appreciated.
任何帮助将不胜感激。
You can use boolean logic:您可以使用布尔逻辑:
select *
from hier
where (@level = 'LEVEL 1' and fc_level1 = @id)
or (@level = 'LEVEL 2' and fc_level2 = @id)
or (@level = 'LEVEL 3' and fc_level3 = @id)
To combine this all into one query:要将所有这些合并到一个查询中:
SELECT h.*
FROM HIER h CROSS JOIN
(SELECT RTRIM(LEVEL_NEW) as LEVEL
FROM HIER
WHERE ID = @ID
) l
WHERE (L.LEVEL = 'LEVEL 1' AND h.FC_LEVEL1 = @ID) OR
(L.LEVEL = 'LEVEL 2' AND h.FC_LEVEL2 = @ID) OR
(L.LEVEL = 'LEVEL 3' AND h.FC_LEVEL3 = @ID) ;
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