Select only half the records

Question

I am trying to figure out how to select half the records where an ID is null. I want half because I am going to use that result set to update another ID field. Then I am going to update the rest with another value for that ID field.

So essentially I want to update half the records someFieldID with one number and the rest with another number splitting the update basically between two values for someFieldID the field I want to update.

Answer 1

In oracle you can use the ROWNUM psuedocolumn. I believe in sql server you can use TOP (e.g., select TOP 50 PERCENT * from table)

Answer 2

You can select by percent:

 SELECT TOP 50 PERCENT *fields* FROM YourTable WHERE ...

Answer 3

update x set id=@value from (select top 50 percent * from table where id is null) x