Sql-server – Transposing repeated rows of datetime into columns

In sql-server-2005 or later, the the UNPIVOT and PIVOT operators can be used:

Sample data:

DECLARE @Source AS TABLE
(
    ID      char(1) PRIMARY KEY,
    PD1     integer NOT NULL,
    PD2     integer NOT NULL,
    PD3     integer NOT NULL,
    PD4     integer NOT NULL,
    PD5     integer NOT NULL
);

INSERT @Source
    (ID, PD1, PD2, PD3, PD4, PD5)
VALUES
    ('A', 1, 2, 3, 4, 5),
    ('B', 6, 7, 8, 9, 0);

Query:

SELECT 
    Pvt.Price, 
    Pvt.A, 
    Pvt.B
FROM @Source AS s
UNPIVOT
(
    Val 
    FOR Price IN (PD1, PD2, PD3, PD4, PD5)
) AS Unpvt
PIVOT 
(
    MAX(Val) 
    FOR ID IN (A, B)
) AS Pvt;

Output:

╔═══════╦═══╦═══╗
║ Price ║ A ║ B ║
╠═══════╬═══╬═══╣
║ PD1   ║ 1 ║ 6 ║
║ PD2   ║ 2 ║ 7 ║
║ PD3   ║ 3 ║ 8 ║
║ PD4   ║ 4 ║ 9 ║
║ PD5   ║ 5 ║ 0 ║
╚═══════╩═══╩═══╝

Execution plan:

The query can also be written without PIVOT and UNPIVOT:

SELECT
    f1.Price,
    A = MAX(CASE WHEN s.ID = 'A' THEN f1.Val END),
    B = MAX(CASE WHEN s.ID = 'B' THEN f1.Val END)
FROM @Source AS s
CROSS APPLY
(
    SELECT 'PD1', s.PD1 UNION ALL
    SELECT 'PD2', s.PD2 UNION ALL
    SELECT 'PD3', s.PD3 UNION ALL
    SELECT 'PD4', s.PD4 UNION ALL
    SELECT 'PD5', s.PD5
) AS f1 (Price, Val)
GROUP BY
    f1.Price;

Try the SQLFiddle here

The question is mainly about how to optimize the select statement:

SELECT [TABLE], [FIELD], [AFTER], [DATE]
FROM mytbl WITH (NOLOCK)
WHERE [TABLE] = 'OTB' AND
[FIELD] = 'STATUS'

Removing the redundant projections and adding the presumed dbo schema:

SELECT [AFTER], [DATE] 
FROM dbo.mytbl WITH (NOLOCK)
WHERE [TABLE] = 'OTB'
AND FIELD = 'STATUS';

Without an index like ([TABLE],[FIELD]) INCLUDE ([AFTER],[DATE]) SQL Server has two main options:

1. Scan the heap entirely (3GB+); or
2. Locate rows matching [TABLE] = 'OTB' and [FIELD] = 'STATUS' (using IDX6), then perform a heap (RID) lookup per row to retrieve the [AFTER] and [DATE] columns.

Whether the optimizer chooses a heap scan or index seek with RID lookup depends on the estimated selectivity of the [TABLE] = 'OTB' and [FIELD] = 'STATUS'predicates. Check to see if the estimated number of rows from the seek matches reality. If not, update your statistics. Test the query with an table hint forcing the use of the index, if that condition is reasonably selective. If the optimizer is currently choosing the index seek, test performance with an INDEX(0) or FORCESCAN hint to scan the heap.

Beyond that, you could look to improve the scan of the heap a little by removing some of the unused space (370MB). In SQL Server 2008 this can be done by rebuilding the heap. Unused space in heaps often results from deletes performed without a table lock being taken (without a table lock, empty pages are not deallocated from a heap). Tables that experience frequent deletions are often better stored as a clustered table for this reason.

The performance of the heap scan depends on how much of the table is stored in memory, how much must be read from disk, how full the pages are, the speed of the persistent storage, whether the scan is I/O or CPU bound (parallelism can help).

If performance is still unacceptable after you have investigated all of the above, try to make the case for a new index. If available on your version of SQL Server, a possible filtered index for the given query would be:

CREATE INDEX index_name
ON dbo.mytbl ([DATE],[AFTER])
WHERE [TABLE] = 'OTB'
AND [FIELD] = 'STATUS';

Also consider index compression, if that is available and beneficial. Without a new index of some kind, there's relatively little you can do to improve the performance of the given query.