Conditional auto increment value in SQL server “SELECT”

Question

Data Available in Table1

ID  Name1   Address
1   nm1     abc
1   nm2     def
1   nm3     ghi
0   nm4     jkl
0   nm5     mno
0   nm6     pqr
1   nm7     stu
1   nm8     vwx
1   nm9     yza
0   nm10    bcd

Expected Output from Table1

ID  Name1   Address Counter
1   nm1      abc      1
1   nm2      def      1
1   nm3      ghi      1
0   nm4      jkl      2
0   nm5      mno      2
0   nm6      pqr      2
1   nm7      stu      3
1   nm8      vwx      3
1   nm9      yza      3
0   nm10     bcd      4

Order must be sort using the key fields and need to generate the auto increment no in the expected output.

Thanks in advance.

Answer 1

You need to know how the rows are order. I suppose this is sample data and in your real scenario you can ordered the data in unique way. With your sample data I am using the following statement to order the rows:

CAST(REPLACE([Name], 'nm', '') AS INT)

There are different solutions of this (some depending on your SQL version, too). If you are using SQL Server 2012+ you can use the LAG function to find if ID value is changed from the previous and current row and then to sum this changes using OVER clause:

DECLARE @DataSource TABLE
(
    [ID] INT
   ,[Name] VARCHAR(12)
   ,[Address] VARCHAR(12)
);

INSERT INTO @DataSource ([ID], [Name], [Address])
VALUES (1, 'nm1', 'abc')
      ,(1, 'nm2', 'def')
      ,(1, 'nm3', 'ghi')
      ,(0, 'nm4', 'jkl')
      ,(0, 'nm5', 'mno')
      ,(0, 'nm6', 'pqr')
      ,(1, 'nm7', 'stu')
      ,(1, 'nm8', 'vwx')
      ,(1, 'nm9', 'yza')
      ,(0, 'nm10', 'bcd');

SELECT *
      ,SUM([change_made]) OVER (ORDER BY  CAST(REPLACE([Name], 'nm', '') AS INT))
FROM
(
    SELECT *
          ,IIF([ID] <> LAG([ID], 1, -1) OVER (ORDER BY CAST(REPLACE([Name], 'nm', '') AS INT)), 1, 0) AS [change_made]
    FROM @DataSource
) DS
ORDER BY CAST(REPLACE([Name], 'nm', '') AS INT);