How to dynamically generate rows based on value in a column

Question

I'm attempting to write a query to denormalize some data for integrating to our data warehouse, specifically around generating some time slots.

In my source system, I have table that has a start time and and end time and then a column that designates how many appointment slots are available per 15 minute interval.

Example:

    Location | Start Time | End Time | Appointment Slots
    A        | 9:00 am    | 5:00 pm  | 2
    B        | 9:00 am    | 5:00 pm  | 1

I have already been able to generate a list of 15 minute blocks using a CTE. However, each 15 minute slot just says that 2 slots are available for location A and 1 slot is available for location B. What I'd like is to be able to generate 2 rows per 15 minutes for location A and 1 row per 15 minutes for location B.

Answer 1

This is an example of when a "Number" table becomes very handy! If you are not familiar with this concept, read this blog post from Adam Machanic: You REQUIRE a Numbers Table

The numbers table is used to join to the Appointment Slots column (in this case) to duplicate each row AppointmentSlots number of times.

-- A simple recreation of your CTE data...
CREATE  TABLE #AppointmentPeriods
(
    AppointmentLocation CHAR(1),
    AppointmentStartTime TIME,
    AppointmentEndTime TIME,
    AppointmentSlotsAvailable SMALLINT
)

INSERT  INTO #AppointmentPeriods VALUES
    ('A', '09:00', '09:15', 2),
    ('A', '09:15', '09:30', 2),
    ('A', '09:30', '09:45', 2),
    -- ....
    ('A', '16:30', '16:45', 2),
    ('A', '16:45', '17:00', 2),
    ('B', '09:00', '09:15', 1),
    ('B', '09:15', '09:30', 1),
    ('B', '09:30', '09:45', 1),
    -- ....
    ('B', '16:30', '16:45', 1),
    ('B', '16:45', '17:00', 1)


-- Numbers table
CREATE  TABLE #Numbers (NumberValue SMALLINT)

INSERT  INTO #Numbers
-- TOP value should be changed so it is greater than the
-- maximum number of potential appointment slots any location can have
SELECT  TOP 20
        ROW_NUMBER() OVER (ORDER BY object_id)
FROM    sys.objects


SELECT  #AppointmentPeriods.*, NumberValue AS AppointmentSlotNumber
FROM    #AppointmentPeriods
        INNER JOIN #Numbers
            ON AppointmentSlotsAvailable >= NumberValue

Query output:

Location | StartTime | EndTime | AppointmentSlots | SlotNumber
A        | 09:00     | 09:15   | 2                | 1
A        | 09:00     | 09:15   | 2                | 2
A        | 09:15     | 09:30   | 2                | 1
A        | 09:15     | 09:30   | 2                | 2
B        | 16:30     | 16:45   | 1                | 1
B        | 16:45     | 17:00   | 1                | 1

PS: There are many ways to generate a numbers table: SO: What is the best way to create and populate a numbers table?