Sql-server – Calculate Total Visits

I am going to assume that there isn't an index on the date columns, otherwise I think that the query would have been structured differently. If there is, you can probably find a better performing one than this.

The advantage of this query is that it can get all the data in one scan. The disadvantage is that it has to sort the data and join EventEmployee on the entire table. So as always, test with your own situation. This query also assumes that the MAX date is either unique or that equivalent rows would be acceptable.

USE AdventureWorks2012
GO
;
WITH Base AS (
   SELECT 
      TransactionHistory.*
      ,ProductVendor.BusinessEntityID
      ,MAX(CASE WHEN TransactionDate < '2008-08-01' THEN TransactionDate END) 
           OVER (PARTITION BY ProductVendor.BusinessEntityID) AS PreviousVendorTransaction
      ,COUNT(CASE WHEN TransactionDate >= '2008-08-01' THEN 1 END ) 
           OVER (PARTITION BY ProductVendor.BusinessEntityID) AS VendorAfterCutoff
   FROM
      Production.TransactionHistory
      -- Doesn't make the most sense, but I need a repeating relation
      INNER JOIN Purchasing.ProductVendor
         ON TransactionHistory.ProductID = ProductVendor.ProductID
),
Filtered AS (
   SELECT
      *
   FROM
      Base
   WHERE
      Base.TransactionDate >= '2008-08-01'
      OR (TransactionDate = PreviousVendorTransaction AND VendorAfterCutoff > 0)
)
SELECT DISTINCT
   TransactionID
   ,ProductID
   ,ReferenceOrderID
   ,ReferenceOrderLineID
   ,TransactionDate
   ,TransactionType
   ,Quantity
   ,ActualCost
   ,ModifiedDate
FROM
   Filtered

Edit:

Hmm, I think I may have to take back my comment on structuring it differently if there are indexes. The other suggestions that I have are probably fairly minor.

• Make sure the query is using the indexes you're expecting it to. Start and End date to build temp table, end date to drive the previous event loop.
• If the query to build the temp table is doing a lookup on the clustered index, it may be better to hold off and do that as part of the main query.
• Try using a cte instead of a temp table. I think that a cte might be more competitive with the way that the query is structured below.
• If you are returning a lot of events, it might be better to pull out the event table lookup to the main query to give the optimizer the option of doing a merge join.
• I don't see a way of optimizing the previous event lookup short of an indexed view.

Here's a query that combines a few of those ideas.

SELECT
    e.[EventID]
INTO #EventTemp
FROM
    [Events] AS e
WHERE
    ( e.[EventStart] >= @StartDate AND e.[EventStart] <= @EndDate )
    OR ( e.[EventEnd] >= @StartDate AND e.[EventEnd] <= @EndDate )

;
WITH PrevEvent AS (
    SELECT
        EmpPrevEvent.[EventID]
    FROM
    (
        SELECT DISTINCT
            ee.[EmployeeID]
        FROM
            #EventTemp
            INNER JOIN [EventEmployee] AS ee ON
                #EventTemp.[EventID] = ee.[EventID]
    ) AS Emp
    CROSS APPLY (
        SELECT TOP 1
            e.[EventID]
        FROM
            [Events] AS e
            INNER JOIN [EventEmployee] AS ee ON
                e.[EventID] = ee.[EventID]
        WHERE
            ee.[EmployeeID] = Emp.[EmployeeID]
            AND e.[EventEnd] < @StartDate
        ORDER BY 
            e.[EventEnd] DESC
    ) AS EmpPrevEvent
)
SELECT
    e.[EventID],
    e.[EventStart],
    e.[EventEnd],
    e.[EventTypeID]
FROM
    [Events] AS e
WHERE
    e.EventID IN (
        SELECT EventID
        FROM #EventTemp
        UNION
        SELECT EventID
        FROM PrevEvent
    )

To address this problem, I did the following (I'm using PostgreSQL for this, but SQL Server has CTEs and RECURSIVE CTEs and window/analytic functions. I doubt if this can be done in MySQL - maybe using variables - not sure). PostgreSQL is as powerful as the big boys - MySQL is really a toy!

Created a table:

CREATE TABLE stock (sku int, datein date, dateout date, status int);

Populated it thus:

INSERT INTO stock VALUES (123, '2015-02-01', '2015-02-05', 1);
INSERT INTO stock VALUES (123, '2015-02-10', '2015-02-10', 1);
INSERT INTO stock VALUES (123, '2015-02-20', NULL,         0);

Then, I constructed the first part of my query. The actual dates to and from will obviously vary depending on the requirements - I assumed that (from the sample data), the OP wanted to look at the month of February. I constructed the following RECURSIVE CTE to construct a list of the days in February - PostgreSQL has the nifty generate_series function, but that's proprietary and I wanted to make my query portable (to the greatest extent possible). This is the best explanation of RCTEs I came across.

WITH RECURSIVE dates (test_date) AS
(
  SELECT '2015-02-01'::DATE
  UNION ALL
  SELECT test_date + 1 FROM dates
  WHERE test_date < '2015-02-28'
)

Now, I thought that the organisation of the raw data was poor, so I used CTEs to rearrange the data.

Get the outdates from the raw data:

out_dates AS
(
  SELECT dateout AS dout FROM stock
)

Get the indates from the raw data:

in_dates AS
(
  SELECT datein AS din FROM stock
)

Then I "transpose" the data - have to use two steps because one cannot use a Window function in a WHERE clause

transpose AS
(
  SELECT lag(dateout) over() AS datein, datein AS dateout FROM stock
  -- WHERE lag(datein) over() IS NOT NULL AND dateout IS NOT NULL <<-- can't use here.
  ORDER BY dateout, datein
)

And then

ranges AS
(
  SELECT * FROM transpose
  WHERE datein IS NOT NULL AND dateout IS NOT NULL
),

The result of this query is:

datein|dateout
2015-02-05|2015-02-10
2015-02-18|2015-02-20

Note that this corresponds to the in and out dates, but now the data is much simpler to handle because it's structure is more logical - it's chronologically coherent - thanks to the use of the LAG window function.

Now, we bring it all together with the next query:

x AS
(
  SELECT test_date, CASE WHEN has_match THEN 1 ELSE 0 END::int AS flag
  FROM 
  (
    SELECT test_date, 
    EXISTS
    (
      SELECT 1 
      FROM ranges 
      WHERE dates.test_date BETWEEN ranges.datein AND ranges.dateout
    ) AS has_match
  FROM dates  
  ) range_checks
)
SELECT * FROM x;

This gives a series of records for the month that are of this form:

test_date|flag
--------------
2015-02-01|0
2015-02-02|0
2015-02-03|0
2015-02-04|0
2015-02-05|1
2015-02-06|1
<other records snipped for brevity>

or use this as the final query

z AS 
(
  SELECT * FROM dates d
  LEFT JOIN ranges r
  ON (d.test_date BETWEEN r.datein AND r.dateout)
)
SELECT * FROM z;

for records of this form:

test_date|datein|dateout
2015-02-01||
2015-02-02||
2015-02-03||
2015-02-04||
2015-02-05|2015-02-05|2015-02-10
2015-02-06|2015-02-05|2015-02-10
<rest of the records snipped for brevity>