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How do I get the column name of a Null table?

Consider the following table

--------------------------------
ID   | ColA    | ColB   | ColC
--------------------------------
1    | ABC     |        |
2    |         | XYZ    |
3    | PQR     |        |
4    | MNO     | PQR    |

I need to get the first free table of a table where ID = 1. How can I do this

For example:

If ID = 1

, next free column ColB


If ID = 2

, next free column ColA


If ID = 3

, next free column ColB


If ID = 4

, next free columnColC

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4 answers


if you want the column name can be done like this:

SQL> select id, cola, colb, colc,
  2         coalesce(nvl2(cola, '', 'COLA'),
                     nvl2(colb, '', 'COLB'),
                     nvl2(colc, '', 'COLC')) first_free_col
  3    from tab;

        ID COL COL COL FIRST_FREE_COL
---------- --- --- --- --------------------------------
         1 ABC         COLB
         2     XYZ     COLA
         3 PQR         COLB
         4 MNO PQR     COLC


or case

SQL> select id, cola, colb, colc,
  2         case when cola is null then 'COLA'
  3          when colb is null then 'COLB'
  4          when colc is null then 'COLC'
  5         end first_free_col
  6    from tab;

        ID COL COL COL FIRST_FREE_COL
---------- --- --- --- --------------------------------
         1 ABC         COLB
         2     XYZ     COLA
         3 PQR         COLB
         4 MNO PQR     COLC
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For sql-server

; (if you want to consider an empty string ( ''

) then use nullif(colName,'') is null)

)



Select Id, case when colA is null then 'colA'
                when colB is null then 'colB'
                when colC is null then 'colC'
                ...
           end freeCol
from yourTable
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Try the following:

select case 
when ColA is not null then 'ColA'
when ColB is not null then 'ColB'
when ColC is not null then 'ColC'

End FirstCol

from test

SQL Fiddle

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you can use the following query in mysql

select ID,if(colA is null,'colA',(if(colB is null,'colB',
(if(colC is null,'colC','no column is null'))))) as Result  from your_table_name

For your example table, if you run my query you get the following result

enter image description here

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