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Please refer to the attached screenshot for the requirement. I have to collapse rows into a single row with latest test_date in one column and second_latest_date in an other column and latest order_number.

Please share the tips to create a SQL Server query that can (a) transform data from the Source table to (b) data as shown in the Target table.

Data sample for the Source table:

Data sample for the Target table:

You should be able to use a common table expression along with the ROW_NUMBER and LEAD windowing functions to help with this problem.

--demo setup based on your sample data

Declare @T table(DIV VARCHAR(20), LS INT, TT VARCHAR(5), TN INT, LAT DECIMAL(7,3), LONG DECIMAL(7,3), [DATE] DATETIME, ORDER_NUM VARCHAR(30))



INSERT INTO @T(DIV, LS, TT, TN, LAT, LONG, [DATE], ORDER_NUM) VALUES

('BRIDGE',4,'M',1,128.2,186.638, '2/11/2019 17:58', '1004085730'),

('BRIDGE',4,'M',1,128.2,186.638, '2/13/2019 15:22', '1004085755'),

('BRIDGE',4,'M',1,128.2,186.638, '2/17/2019 14:22', '1004104405'),

('CROSS',4,'M',1,170.4,190.2, '2/1/2019 14:22', '1004104405'),

('CROSS',4,'M',1,170.4,190.2, '2/10/2019 14:22', '1004104520'),

('CROSS',4,'M',1,170.4,190.2, '2/17/2019 14:22', '1004104590')



--the query

;WITH CTE

AS (

    SELECT *

        ,ROW_NUMBER() OVER (

            PARTITION BY DIV ORDER BY [DATE] DESC

            ) AS rn

        ,LEAD([date]) OVER (

            PARTITION BY div ORDER BY [date] DESC

            ) AS prev

    FROM @T

    )

SELECT div,ls,tt,tn,lat,long,[date] AS Latest_Test_Date,prev AS Second_Latest_Dte,ORDER_NUM

FROM CTE

WHERE rn = 1

| div    | ls | tt | tn | lat     | long    | Latest_Test_Date        | Second_Latest_Dte       | ORDER_NUM  |

|--------|----|----|----|---------|---------|-------------------------|-------------------------|------------|

| BRIDGE | 4  | M  | 1  | 128.200 | 186.638 | 2019-02-17 14:22:00.000 | 2019-02-13 15:22:00.000 | 1004104405 |

| CROSS  | 4  | M  | 1  | 170.400 | 190.200 | 2019-02-17 14:22:00.000 | 2019-02-10 14:22:00.000 | 1004104590 |

By selecting directly from the common table expresssion
SELECT * FROM CTE

| DIV    | LS | TT | TN | LAT     | LONG    | DATE                    | ORDER_NUM  | rn | prev                    |

|--------|----|----|----|---------|---------|-------------------------|------------|----|-------------------------|

| BRIDGE | 4  | M  | 1  | 128.200 | 186.638 | 2019-02-17 14:22:00.000 | 1004104405 | 1  | 2019-02-13 15:22:00.000 |

| BRIDGE | 4  | M  | 1  | 128.200 | 186.638 | 2019-02-13 15:22:00.000 | 1004085755 | 2  | 2019-02-11 17:58:00.000 |

| BRIDGE | 4  | M  | 1  | 128.200 | 186.638 | 2019-02-11 17:58:00.000 | 1004085730 | 3  | NULL                    |

| CROSS  | 4  | M  | 1  | 170.400 | 190.200 | 2019-02-17 14:22:00.000 | 1004104590 | 1  | 2019-02-10 14:22:00.000 |

| CROSS  | 4  | M  | 1  | 170.400 | 190.200 | 2019-02-10 14:22:00.000 | 1004104520 | 2  | 2019-02-01 14:22:00.000 |

| CROSS  | 4  | M  | 1  | 170.400 | 190.200 | 2019-02-01 14:22:00.000 | 1004104405 | 3  | NULL                    |

you can see that the rn=1 rows are the latest row for each DIV. The LEAD window function looks to the row just before the latest row for that DIV to pick up the second_latest_date.

Update: based on your comment about wanting to union multiple tables before applying the windowing functions, you could use an inline table expression like this:

;WITH CTE

AS (

    SELECT *

        ,ROW_NUMBER() OVER (

            PARTITION BY DIV ORDER BY [DATE] DESC

            ) AS rn

        ,LEAD([date]) OVER (

            PARTITION BY div ORDER BY [date] DESC

            ) AS prev

    FROM 

        (

        select cols from TableOne

        UNION

        select cols from TableTwo

        ) as t

    )