how to update a column for all rows in a table with different values for each row in a table of 100 records

Question

my table contains 100 records and i need to update a column with new values(diff value for each record) for each of the 100 records.How can i do this. the column to update the values is not primary key.

Answer 1

UPDATE tablename
   SET columnname = CASE id
                        WHEN 1 THEN 42
                        WHEN 2 THEN 666
                    END

With this query columnname will be updated to 42 for the row with id = 1 , and 666 for id = 2

Answer 2

Create a table with an autoicrement id and the columns of the original table.

Then

INSERT INTO new_table (column1, column2,.....) -- refer all columns except autoincrement id
SELECT * FROM old_table

Update the old table by joining with the new, assuming the is a key composite or not that distincts each row

Answer 3

load a DataTable say dt with specific row ID of the table which you wanna update. then execute

foreach(DataRow rw in dt.Rows)
{
    update table_name set column_name=desired_value where specific_column=rw
}

Answer 4

Set Unique constraint on this column.

ALTER TABLE YourTableName
ADD CONSTRAINT uc_ColumnID UNIQUE (ColumnName)

Now, whenever you try to update it with duplicate values, sql server will not allow:)

Also a long run scenario

Answer 5

If you're on SQL Server 2005 or newer (you didn't exactly specify.....), you could easily use a CTE (Common Table Expression) for this - basically, you select your PK value, and a counter counting up from 1, and you set each row's ColumnName column to the value of the counter:

;WITH UpdateData AS 
(
   SELECT 
      PKValue,
      ROW_NUMBER() OVER(ORDER BY .......) AS 'RowNum'
   FROM
      dbo.YourTable
)
UPDATE dbo.YourTable
SET ColumnName = u.RowNum
FROM UpdateData u
WHERE dbo.YourTable.PKValue = u.PKValue

With this, you're generating a sequence from 1 through 100 in the RowNum field of the CTE, and you're setting this unique value to your underlying table.