SQL Functions Advance

1] Use CONVERT() to SELECT and GROUP BY the date portion of the StartDate  

SELECT

  -- Select the date portion of StartDate

  CONVERT(DATE, StartDate) as StartDate,

  -- Measure how many records exist for each StartDate

  COUNT(StartDate) as CountOfRows 

FROM CapitalBikeShare 

-- Group by the date portion of StartDate

GROUP BY CONVERT(DATE, StartDate)

-- Sort the results by the date portion of StartDate

ORDER BY CONVERT(DATE, StartDate)




2]

  • Use DATENAME() to SELECT the weekday value for the StartDate.
  • Use SUM() and DATEDIFF() to calculate TotalTripHours. (beginning with seconds).
  • Group by the DATENAME() result and summarize TotalTripHours.
  • Order TotalTripHours in descending order.

Ans - 

SELECT
    -- Select the day of week value for StartDate
DATENAME(Weekday, StartDate) as DayOfWeek,
    -- Calculate TotalTripHours
SUM(DATEDIFF(ss, StartDate, EndDate))/ 3600 as TotalTripHours 
FROM CapitalBikeShare 
-- Group by the day of week
GROUP BY DATENAME(WEEKDAY,StartDate)
-- Order TotalTripHours in descending order
ORDER BY TotalTripHours DESC;


3 
  • Use SUM() and DATEDIFF() to find the Total Ride Hours per day starting from seconds.
  • Use CONVERT() to SELECT the date portion of StartDate.
  • Use DATENAME() and CONVERT() to select the WEEKDAY.
  • Use WHERE to only include Saturdays


Answer 

SELECT
-- Calculate TotalRideHours using SUM() and DATEDIFF()
  SUM(DATEDIFF(SECOND, StartDate, EndDate))/ 3600 AS TotalRideHours,
    -- Select the DATE portion of StartDate
  CONVERT(DATE, StartDate) AS DateOnly,
    -- Select the WEEKDAY
  DATENAME(WEEKDAY, CONVERT(DATE, StartDate)) AS DayOfWeek 
FROM CapitalBikeShare
-- Only include Saturday
WHERE DATENAME(WEEKDAY, StartDate) = 'Saturday' 
GROUP BY CONVERT(DATE, StartDate);




DECLARE VARIABLE Function Syntax


  • Create a time variable named @ShiftStartTime and set initial value to '08:00 AM'.
  • Create a date variable named @StartDate and set it to the first StartDate from the BikeShare table.
  • Create a datetime variable named `@ShiftStartDateTime.
  • Change @StartDate and @ShiftStartTime to datetime data types and assign to @ShiftStartDateTime


Answer - 


-- Create @ShiftStartTime
DECLARE @ShiftStartTime AS time = '08:00 AM'

-- Create @StartDate
DECLARE @StartDate AS date

-- Set StartDate to the first StartDate from CapitalBikeShare
SET 
@StartDate = (
    SELECT TOP 1 StartDate 
    FROM CapitalBikeShare 
    ORDER BY StartDate ASC
)

-- Create ShiftStartDateTime
DECLARE @ShiftStartDateTime AS datetime

-- Cast StartDate and ShiftStartTime to datetime data types
SET @ShiftStartDateTime = CAST(@StartDate AS datetime) + CAST(@ShiftStartTime AS datetime) 

SELECT @ShiftStartDateTime



Declare Syntax

  • Use DECLARE to create a TABLE variable named @Shifts
  • The @Shifts table variable should have the following columns - StartDateTime and EndDateTime - both of datetime data type.
  • Populate the table variable with the values '3/1/2018 8:00 AM' and '3/1/2018 4:00 PM'.


-- Declare @Shifts as a TABLE
DECLARE @Shifts TABLE(
    -- Create StartDateTime column
StartDateTime datetime ,
    -- Create EndDateTime column
EndDateTime datetime)
-- Populate @Shifts
INSERT INTO @shifts (StartDateTime, EndDateTime)
SELECT '3/1/2018 8:00 AM', '3/1/2018 4:00 PM'
SELECT * 
FROM @Shifts




4. 
  • Declare a TABLE variable named @RideDates with the following columns RideStart and RideEnd.
  • Both table variable columns should be date data type.
  • SELECT the unique values of StartDate and EndDate from the CapitalBikeShare table. CAST them from datetime to date data types.
  • Store the query results in @RideDates

-- Declare @RideDates
DECLARE @RideDates TABLE(
    -- Define RideStart column
RideStart date, 
    -- Define RideEnd column
    RideEnd date)
-- Populate @RideDates
INSERT INTO @RideDates(RideStart, RideEnd)
-- Select the unique date values of StartDate and EndDate
SELECT DISTINCT
    -- Cast StartDate as date
CAST(StartDate as date),
    -- Cast EndDate as date
CAST(EndDate as date) 
FROM CapitalBikeShare 
SELECT * 
FROM @RideDates



Here you will use the GETDATE(), DATEDIFF(), and DATEADD() functions to find the first day of the current month.


SELECT DATEADD(month, DATEDIFF(month, 0, GETDATE()), 0)

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