Sunday, 29 January 2017

Create and populate Time Dimension

We have sensors in our building that output data every minute which we want to use in a dimensional model. Therefore we need a Time Dimension to aggregate data on parts of the day. How do you create and populate a Time Dimension?
International Time Dimension

Since creating and populating a Time Dimension is a one-time job, T-SQL is probably the best way to accomplish this. For this example we need a Time Dimension on minute level and therefore we have created a loop that executes a insert query 1440 times (24hours * 60minutes).

Besides the hours and minutes we also want to add a name of the day part in two languages and a couple of time strings in both 12 and 24hour notation to make this dimension usable for various countries.

-- Drop the table if it already exists
IF OBJECT_ID('dbo.DimTime', 'U') IS NOT NULL 
    DROP TABLE dbo.DimTime;

-- Then create a new table
CREATE TABLE [dbo].[DimTime](
    [TimeId] [int] IDENTITY(1,1) NOT NULL,
    [Time] [time](0) NULL,
    [Hour] [int] NULL,
    [Minute] [int] NULL,
    [MilitaryHour] int NOT null,
    [MilitaryMinute] int NOT null,
    [AMPM] [varchar](2) NOT NULL,
    [DayPartEN] [varchar](10) NULL,
    [DayPartNL] [varchar](10) NULL,
    [HourFromTo12] [varchar](17) NULL,
    [HourFromTo24] [varchar](13) NULL,
    [Notation12] [varchar](10) NULL,
    [Notation24] [varchar](10) NULL

-- Needed if the dimension already existed
-- with other column, otherwise the validation
-- of the insert could fail.

-- Create a time and a counter variable for the loop
DECLARE @Time as time;
SET @Time = '0:00';

DECLARE @counter as int;
SET @counter = 0;

-- Two variables to store the day part for two languages
DECLARE @daypartEN as varchar(20);
set @daypartEN = '';

DECLARE @daypartNL as varchar(20);
SET @daypartNL = '';

-- Loop 1440 times (24hours * 60minutes)
WHILE @counter < 1440

    -- Determine datepart
    SELECT  @daypartEN = CASE
                         WHEN (@Time >= '0:00' and @Time < '6:00') THEN 'Night'
                         WHEN (@Time >= '6:00' and @Time < '12:00') THEN 'Morning'
                         WHEN (@Time >= '12:00' and @Time < '18:00') THEN 'Afternoon'
                         ELSE 'Evening'
    ,       @daypartNL = CASE
                         WHEN (@Time >= '0:00' and @Time < '6:00') THEN 'Nacht'
                         WHEN (@Time >= '6:00' and @Time < '12:00') THEN 'Ochtend'
                         WHEN (@Time >= '12:00' and @Time < '18:00') THEN 'Middag'
                         ELSE 'Avond'

    INSERT INTO DimTime ([Time]
                       , [Hour]
                       , [Minute]
                       , [MilitaryHour]
                       , [MilitaryMinute]
                       , [AMPM]
                       , [DayPartEN]
                       , [DayPartNL]
                       , [HourFromTo12]
                       , [HourFromTo24]
                       , [Notation12]
                       , [Notation24])
                VALUES (@Time
                       , DATEPART(Hour, @Time) + 1
                       , DATEPART(Minute, @Time) + 1
                       , DATEPART(Hour, @Time)
                       , DATEPART(Minute, @Time)
                       , CASE WHEN (DATEPART(Hour, @Time) < 12) THEN 'AM' ELSE 'PM' END
                       , @daypartEN
                       , @daypartNL
                       , CONVERT(varchar(10), DATEADD(Minute, -DATEPART(Minute,@Time), @Time),100)  + ' - ' + CONVERT(varchar(10), DATEADD(Hour, 1, DATEADD(Minute, -DATEPART(Minute,@Time), @Time)),100)
                       , CAST(DATEADD(Minute, -DATEPART(Minute,@Time), @Time) as varchar(5)) + ' - ' + CAST(DATEADD(Hour, 1, DATEADD(Minute, -DATEPART(Minute,@Time), @Time)) as varchar(5))
                       , CONVERT(varchar(10), @Time,100)
                       , CAST(@Time as varchar(5))

    -- Raise time with one minute
    SET @Time = DATEADD(minute, 1, @Time);

    -- Raise counter by one
    set @counter = @counter + 1;

Below a very basic example of the usage of this Time Dimension. The LightsAttrium is 0 or 1 indicating whether the lights in the atrium are on or off. By using the average of that during a daypart (night, moning, etc) it shows the percentage of the lights being on. At night it's almost always on and during the afternoon it's off most of the time.
Basic example of usage.

Above a very complete, but yet still basic, example of a Time Dimension. You can add or remove columns for your own specific purposes (let us know the additions in the comments below). Extending this to for example seconds is very easy. Just change the 1440 in the WHILE to 86400 (24*60*60) and change the DATEADD at the bottom to "second" instead of "minute".

Thursday, 5 January 2017

Azure Snack - Grant Access to your Azure SQL DB

You want to give an user permission to connect to your database in Azure through SQL Server Management Studio. How do you do this?

In SQL Server Management Studio (SSMS) with an on-premise database you can do a lot with a GUI, like creating an user and giving this user the right permissions. In this case we use SQL Server Authentication. With a database in Azure you have to write code in Transact-SQL for this, instead of using GUI. Of course you can also use T-SQL in combination with an on-premise database, but for the convenience I use a GUI. Unfortunately, this GUI is not supported in an Azure database. Just like 'IntelliSense' for example.

When you connect to your database server and you want to create a new login, you will see two different windows: a GUI within an on-premise database and a new query window in an Azure database. We will continue with query's, which needs to be run in a particular order.

SSMS - SQL Server on-premise versus Azure SQL Server

1) Create new login
First we need to create a new login to grant access to the database server. Therefore you have to be administrator on the database server. Click on the Security folder and then on Logins to create a 'New Login...'.

Then we edit the generated query to this:

CREATE LOGIN [RobertSmith] 
WITH PASSWORD = 'Abcdefg123!' 

The password must include letters, numbers, symbols and have a minimum length.

2) Create user 
When we have created the login, we can link this login to a specific database (user). Click on the Security folder in the specific database and then on Users to create a 'New User...'. The engine also generates a code at this point.

We change the generated query to:

USE [sensory]

CREATE USER [RobertSmith]
FOR LOGIN [RobertSmith]

3) Permissions
Once the user has been created, you can further specify the authorization . For example, read access to one of more schemas. This can be done by the following query:

USE [sensory]

GRANT select ON SCHEMA :: [analyse] TO [RobertSmith] 

Now the user can login with SQL Authentication with the created credentials. Important is to select the right database, otherwise SSMS will automatically make connection to the master database. In this case we gave permissions to a specific database, so the attempt will fail.

SSMS - Select the database before connecting to server

This isn't very difficult to understand for anybody with some experience within SSMS, but this is not a daily action and in that scenario there is a chance that you do not have the query's ready. Anyway, for now you have to do it with T-SQL in Azure, but perhaps in the future also with an GUI.

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