SQL query to get column names if it has specific value - sql

Question

I have a situation here, I have a table with a flag assigned to the column names(like 'Y' or 'N'). I have to select the column names of a row, if it have a specific value.
My Table:
Name|sub-1|sub-2|sub-3|sub-4|sub-5|sub-6|
-----------------------------------------
Tom | Y | | Y | Y | | Y |
Jim | Y | Y | | | Y | Y |
Ram | | Y | | Y | Y | |
So I need to get, what are all the subs are have 'Y' flag for a particular Name.
For Example:
If I select Tom I need to get the list of 'Y' column name in query output.
Subs
____
sub-1
sub-3
sub-4
sub-6
Your help is much appreciated.

Answer 1

The problem is that your database model is not normalized. If it was properly normalized the query would be easy. So the workaround is to normalize the model "on-the-fly" to be able to make the query:
select col_name
from (
select name, sub_1 as val, 'sub_1' as col_name
from the_table
union all
select name, sub_2, 'sub_2'
from the_table
union all
select name, sub_3, 'sub_3'
from the_table
union all
select name, sub_4, 'sub_4'
from the_table
union all
select name, sub_5, 'sub_5'
from the_table
union all
select name, sub_6, 'sub_6'
from the_table
) t
where name = 'Tom'
and val = 'Y'
The above is standard SQL and should work on any (relational) DBMS.

Answer 2

Below code works for me.
select t.Subs from (select name, u.subs,u.val
from TableName s
unpivot
(
val
for subs in (sub-1, sub-2, sub-3,sub-4,sub-5,sub-6,sub-7)
) u where u.val='Y') T
where t.name='Tom'

Answer 3

Somehow I am near to the solution. I can get for all rows. (I just used 2 columns)
select col from ( select col, case s.col when 'sub-1' then sub-1 when 'sub-2' then sub-2 end AS val from mytable cross join ( select 'sub-1' AS col union all select 'sub-2' ) s ) s where val ='Y'
It gives the columns for all row. I need the same data for a single row. Like if I select "Tom", I need the column names for 'Y' value.

Answer 4

I'm answering this under a few assumptions here. The first is that you KNOW the names of the columns of the table in question. Second, that this is SQL Server. Oracle and MySql have ways of performing this, but I don't know the syntax for that.
Anyways, what I'd do is perform an 'UNPIVOT' on the data.
There's a lot of parans there, so to explain. The actual 'unpivot' statement (aliased as UNPVT) takes the data and twists the columns into rows, and the SELECT associated with it provides the data that is being returned. Here's I used the 'Name', and placed the column names under the 'Subs' column and the corresponding value into the 'Val' column. To be precise, I'm talking about this aspect of the above code:
SELECT [Name], [Subs], [Val]
FROM
(SELECT [Name], [Sub-1], [Sub-2], [Sub-3], [Sub-4], [Sub-5], [Sub-6]
FROM pvt) p
UNPIVOT
(Orders FOR [Name] IN
([Name], [Sub-1], [Sub-2], [Sub-3], [Sub-4], [Sub-5], [Sub-6])
)AS unpvt
My next step was to make that a 'sub-select' where I could find the specific name and val that was being hunted for. That would leave you with a SQL Statement that looks something along these lines
SELECT [Name], [Subs], [Val]
FROM (
SELECT [Name], [Subs], [Val]
FROM
(SELECT [Name], [Sub-1], [Sub-2], [Sub-3], [Sub-4], [Sub-5], [Sub-6]
FROM pvt) p
UNPIVOT
(Orders FOR [Name] IN
([Name], [Sub-1], [Sub-2], [Sub-3], [Sub-4], [Sub-5], [Sub-6])
)AS unpvt
) AS pp
WHERE 1 = 1
AND pp.[Val] = 'Y'
AND pp.[Name] = 'Tom'

Answer 5

select col from (
select col,
case s.col
when 'sub-1' then sub-1
when 'sub-2' then sub-2
when 'sub-3' then sub-3
when 'sub-4' then sub-4
when 'sub-5' then sub-5
when 'sub-6' then sub-6
end AS val
from mytable
cross join
(
select 'sub-1' AS col union all
select 'sub-2' union all
select 'sub-3' union all
select 'sub-4' union all
select 'sub-5' union all
select 'sub-6'
) s on name="Tom"
) s
where val ='Y'
included the join condition as
on name="Tom"