TSQL: How to update each record with forreign key -

i have old table in ms sql not has primary key. structure is:

• document
• position
• material
• quantity
• ..

i want change that, , put "document" , "position" keys of table. of course each combination should unique. new records done old 1 "position" field missing.

what want update of existing record position null incrementational number (each time change document change, counter should start again @ 1)

what should tsql sentence in order quickly?

thank youit

you can use cte , ranking function row_number:

with cte as(     select document, position, material, quantity,         rn = row_number() on (partition document order document asc)     dbo.tablename ) update cte set position = rn position null 

if need specific logic order change order document asc meaningful.

if want see updated have change update select * cte position null. that's 1 of benefits of common-table-expression(cte).