Question

I have a table columns Id and EmployeeID. The table data has the following peculiarity: in some parts (where the Id is consecutive), the same EmployeeID can sometimes be found, for example

Id | EmployeeID
---------------
1  |     1
2  |     1
3  |     2
4  |     5
5  |     1
6  |     1

I want to build a query to find blocks of data containing the same EmployeeID where the Id is consecutive (with a minimum value of x records). So far I came up with:

SELECT EmployeeID, MIN(Id), MAX(Id), COUNT(*)
FROM recs
GROUP BY EmployeeID
HAVING COUNT(*) > 5 AND
       MAX(Id) - MIN(Id) + 1 = COUNT(*)

This query will bring me some (but not all) blocks of data, as long as the same Employee can only be found in a single block. Can anyone come up with a solution which will provide all different blocks of data for each employee?

Answer 1

Not the best solution, but it should work (for example, 3 consecutive ids):

SELECT Id, EmployeeID FROM
(
SELECT r.Id, r.EmployeeID, 
(SELECT COUNT(1) FROM recs r1 WHERE (r1.EmployeeID = r.EmployeeID AND r1.id = r.Id-1) AS c1,
(SELECT COUNT(1) FROM recs r2 WHERE (r2.EmployeeID = r.EmployeeID AND r2.id = r.Id-2) AS c2,
(SELECT COUNT(1) FROM recs r3 WHERE (r3.EmployeeID = r.EmployeeID AND r3.id = r.Id-3) AS c3
FROM recs r1) tab1
WHERE (tab1.c1+tab1.c2+tab1.c3 =3);

I suggested that Id is a primary(or a unique) key. If it’s not, you should change a little each of sub-queries to something like SELECT IF(COUNT(1) >0,1,0) …..