Make rownum value null in the same values - sql

Question

I have the sql code and i want for every unique value from COLUMN1 the same rownum.
For example in the example i want null values for rownum 2,3 and for column 2 rownum 2
select rownum,
t1.column1 as column1,
t1.Column2 as column2,
t3.Column3 as column3
from Table1 t1,Table3 t3,Table2 t2
where t3.S_ID=t2.AS_ID
and t2.KT_ID=t1.T_ID
How can i implement this?

Answer 1

First, learn proper explicit join syntax. Second, you can readily do what you want using lag() and other analytic functions:
select (case when column1 = lag(column1) over (order by column1, column3)
then NULL
else dense_rank() over (order by column1)
end) as rn,
t1.column1 as column1,
t1.Column2 as column2,
t3.Column3 as column3
from Table1 t1 join
Table2 t2
on t2.KT_ID = t1.T_ID join
Table3 t3
on t3.S_ID = t2.AS_ID
order by column1, column3;
Some notes:
SQL queries return unordered result sets. If you want rows in a particular order -- or even in the same order the next time you run the query -- then include an order by.
I arbitrarily added column3 to the ordering. It can be any column that makes the sort stable. That is, each row has a unique set of order keys, so they are in the same order each time.
The same ordering conditions are used for the lag() functions, but only column1 is used for the dense_rank().
Learn explicit join syntax. It is more powerful, and almost everyone thinks it is easier to read.

Answer 2

select
case when row_number() -- if it's the first row per group...
over(partition by column1
order by column3) = 1
then dense_rank() -- ... return 1,2,3
over(order by column1)
else null
end,
t1.column1 as column1,
t1.Column2 as column2,
t3.Column3 as column3
from Table1 t1,Table3 t3,Table2 t2
where t3.S_ID=t2.AS_ID
and t2.KT_ID=t1.T_ID

Answer 3

This might help you...
select rownum,column1,column2,column3 from (
Select rownum,column1,column2,column3,
row_number() over( partition by column1,column2 order by column1,column2) as analytic_rnm
from(
select rownum,
column1 as column1,
Column2 as column2,
Column3 as column3
from Table1 t1,Table3 t3,Table2 t2
where t3.S_ID=t2.AS_ID
and t2.KT_ID=t1.T_ID
)X
)M
where analytic_rnm=1
union all
select NULL as rownum,
column1,column2,column3 from (
Select rownum,column1,column2,column3,
row_number() over( partition by column1,column2 order by column1,column2) as analytic_rnm
from(
select rownum,
column1 as column1,
Column2 as column2,
Column3 as column3
from Table1 t1,Table3 t3,Table2 t2
where t3.S_ID=t2.AS_ID
and t2.KT_ID=t1.T_ID
)X)Y
where analytic_rnm>1