MS SQL Azure – Creating contained users – SQL Authentication

In every database engine it is important to create logins that enforce security around your database and that can be maintained.
Additionally if you are working for a client you may wish to transfer this database at some point in the future to the client.

In SQL Azure users can be created against the master database in the instance and the role can then be transferred to individual databases.

Fine but if you wish to transfer the database the roles will be compromised and error when the database is moved.
One suggestion to avoid this issue is to use contained users.

Using your sys admin account connect to the database and run;

CREATE USER rocketengineapplication WITH PASSWORD = 'bluedanube';
ALTER ROLE db_owner ADD MEMBER rocketengineapplication;

Now developers could use this password and username to login to the database and do most of what is required without having any privileges to the SQL Server and if you ever transfer the database the role will pass with the database.

Here is a link to built in database roles
SQL Database Roles

Secure a single or pooled database in SQL Azure

and here is a useful query that can be run to identify the users and roles that a particular database has. This allows you to check what users are on a database and what are there roles.

SELECT u.name AS UserName, u.type_desc AS UserType, r.name AS RoleName
FROM sys.database_principals AS u
LEFT JOIN sys.database_role_members AS rm ON rm.member_principal_id = u.principal_id
LEFT JOIN sys.database_principals AS r ON r.principal_id = rm.role_principal_id
WHERE
    u.type NOT IN('R', 'G')
ORDER BY
      UserName
    , RoleName;

MS SQL Azure – Computed Columns

It can be really nice to create a computed column and add it to the table rather than adding it in a field

This would work well using the function listed in the previous post where I automatically calculate the age of trees.

Add Computed Column to SQL Azure Table

ALTER TABLE dbo.t001trees ADD treeage AS (dbo.functionyearmonthday(dbo.t001trees.plantdate, GETDATE()));

This will appear in the table and look like it is an actual field but it is calculated and will not keep the figures in the table unless you specify persistance

see the above link for further reading on this topic

MS SQL Azure – TSQL to name the age between dates in text

It is relatively easy to calculate the number of either years, months days hours or seconds between two dates using the native DATEDIFF built in function which comes with SQL.

e.g.

SELECT dbo.t001trees.pkid, 
dbo.t001trees.plantdate, 
DATEDIFF(Year, dbo.t001trees.plantdate, GETDATE()) as treeage 
from dbo.t001trees;

But here is a function that will spell it out into a string that reads something like
2 days
1 month 2 days
2 years 1 month 2 days

CREATE OR ALTER FUNCTION dbo.functionyearmonthday
(
@datefrom Date,
@dateto Date
)
RETURNS varchar(100)
as
BEGIN
DECLARE @date1 DATETIME, @date2 DATETIME, @result VARCHAR(100);
DECLARE @years INT, @months INT, @days INT;

SET @date1 = @datefrom
SET @date2 = @dateto

SELECT @years = DATEDIFF(yy, @date1, @date2)
IF DATEADD(yy, -@years, @date2) < @date1
SELECT @years = @years-1
SET @date2 = DATEADD(yy, -@years, @date2)

SELECT @months = DATEDIFF(mm, @date1, @date2)
IF DATEADD(mm, -@months, @date2) < @date1
SELECT @months=@months-1
SET @date2= DATEADD(mm, -@months, @date2)

SELECT @days=DATEDIFF(dd, @date1, @date2)
IF DATEADD(dd, -@days, @date2) < @date1
SELECT @days=@days-1
SET @date2= DATEADD(dd, -@days, @date2)

SELECT @result= ISNULL(CAST(NULLIF(@years,0) AS VARCHAR(10)) + ' years ','')
+ ISNULL(' ' + CAST(NULLIF(@months,0) AS VARCHAR(10)) + ' months ','')
+ ISNULL(' ' + CAST(NULLIF(@days,0) AS VARCHAR(10)) + ' days','')

RETURN @result;
END

And if you would like to call the function from another query here is an example

SELECT dbo.functionyearmonthday(dbo.t001trees.plantdate, GETDATE()) as treeage FROM dbo.t001trees

That is enough for most people but it can be expanded to include hours minutes seconds and milliseconds which could be useful if you need more precision it can be seen that the DATEDIFF native function is included extensively within this function.

CREATE OR ALTER FUNCTION dbo.functiontimeperiodmoreprecision
(
@datefrom Date,
@dateto Date
)
RETURNS varchar(100)
as
BEGIN
DECLARE @date1 DATETIME, @date2 DATETIME, @result VARCHAR(100);
DECLARE @years INT, @months INT, @days INT,
@hours INT, @minutes INT, @seconds INT, @milliseconds INT;

SET @date1 = @datefrom
SET @date2 = @dateto

SELECT @years = DATEDIFF(yy, @date1, @date2)
IF DATEADD(yy, -@years, @date2) < @date1
SELECT @years = @years-1
SET @date2 = DATEADD(yy, -@years, @date2)

SELECT @months = DATEDIFF(mm, @date1, @date2)
IF DATEADD(mm, -@months, @date2) < @date1
SELECT @months=@months-1
SET @date2= DATEADD(mm, -@months, @date2)

SELECT @days=DATEDIFF(dd, @date1, @date2)
IF DATEADD(dd, -@days, @date2) < @date1
SELECT @days=@days-1
SET @date2= DATEADD(dd, -@days, @date2)

SELECT @hours=DATEDIFF(hh, @date1, @date2)
IF DATEADD(hh, -@hours, @date2) < @date1
SELECT @hours=@hours-1
SET @date2= DATEADD(hh, -@hours, @date2)

SELECT @minutes=DATEDIFF(mi, @date1, @date2)
IF DATEADD(mi, -@minutes, @date2) < @date1
SELECT @minutes=@minutes-1
SET @date2= DATEADD(mi, -@minutes, @date2)

SELECT @seconds=DATEDIFF(s, @date1, @date2)
IF DATEADD(s, -@seconds, @date2) < @date1
SELECT @seconds=@seconds-1
SET @date2= DATEADD(s, -@seconds, @date2)

SELECT @milliseconds=DATEDIFF(ms, @date1, @date2)

SELECT @result= ISNULL(CAST(NULLIF(@years,0) AS VARCHAR(10)) + ' years,','')
+ ISNULL(' ' + CAST(NULLIF(@months,0) AS VARCHAR(10)) + ' months,','')
+ ISNULL(' ' + CAST(NULLIF(@days,0) AS VARCHAR(10)) + ' days,','')
+ ISNULL(' ' + CAST(NULLIF(@hours,0) AS VARCHAR(10)) + ' hours,','')
+ ISNULL(' ' + CAST(@minutes AS VARCHAR(10)) + ' minutes and','')
+ ISNULL(' ' + CAST(@seconds AS VARCHAR(10))
+ CASE
WHEN @milliseconds > 0
THEN '.' + CAST(@milliseconds AS VARCHAR(10))
ELSE ''
END
+ ' seconds','')

RETURN @result
END

MS Access Function : Function to create SQL union queries

Another small function that can speed up the text required to be written for large union queries.

Typically this can be used with
MS Access Function : Scan through a directory and write list of files to a table.

There are a number of data providers that provide data files broken down into different geographical areas. In previous posts I have outlined how we can get these all into Postgis. But once they are in postgis (or any other database) you may wish to get these separate tables into one single global table. Clearly a union query will do this, however it can be time consuming to write the union query out as it simply has so many tables in it.

I used the code in the link to scan a directory and get all the filenames (in this case shape files of the UK road network) into a table that I called UKRoadLinks which had two fields PKID (primary long integer autonumber) and Filen text field where Filen were the filenames.

I then wrote the following function to write a text file that on completion will contain an sql union of all the tables listed in your recordset – I then copied and pasted this into Postgis database within which I had already imported all the sub tables to union the tables into a single copy. Alter the recordset source if for instance if you wish to use only a subset. The nice thing about this is if you have hundreds of tables to amalgamate there should be less likelyhood of you accidentally missing or misspelling table names.

Public Function createunionsqllinks()

Dim rst As DAO.Recordset
Set rst = CurrentDb.OpenRecordset("UKRoadLinks")

Dim fs, TextFile
Set fs = CreateObject("Scripting.FileSystemObject")
Set TextFile = fs.CreateTextFile("c:\data\sqlmerge.txt", True)
TextFile.WriteLine ("CREATE TABLE sqltomergetables AS ")
Do Until rst.EOF = True
TextFile.WriteLine (Chr$(40) & "select * from " & rst!Filen & Chr$(41) & " UNION ")
rst.MoveNext
Loop
rst.Close
TextFile.WriteLine (";")
TextFile.Close

MsgBox "Created"

End Function

018 Postgres : Export Data and Structure of a Single database from a Postgres instance / Import Data and Structure of a Single database into a Postgres Instance

Demonstration environment and programs
Windows 10
Postgres Version : 11.2
QGIS desktop version : 3.4.4

My working through of a process to export a single database (structure and data) from a Postgres Instance, the database has PostGIS and pgrouting extensions enabled, followed by importing into in this example the same instance but in principle could be a different instance.
Access the command prompt (RUN AS ADMINISTRATOR)

PLEASE NOTE run the command prompt as administrator or you will get frequently get an ACCESS DENIED message after using pg dump command.

Navigate to the directory of the PostgresVersion from which you wish to export the database. This will typically be the bin subdirectory of the version of your postgres ( here 11 ). You can ensure that pg_dump.exe is here if you do a dir on the directory to reveal alternatively you could reference the full path to pgdump and then pass the parameters to it subsequently.

eg

Next place in the parameters of the database what database you wish to export along with the name that you want to call the exported file and then hit return.

pg_dump -U postgres -p 5432 edinburghrouting > c:\dbexport.pgsql

Hitting return depending on the security of your instance you will be prompted for a password.

Enter the password hit return

When I do this on my home computer there is no return message but going into the C drive I can see that dbexport.pgsql now exists.

Next we want to create a blank database this is required to import the data and structure into.
This we do in psql signed in as a user with sufficient privelege.

Now back in the command line running as administrator we can run the following.

psql -U postgres importededinburghrouting < c:\dbexport.pgsql

Pressing return depending on your security you should be asked for your password.

Once this is done it goes through a process of recreating the structure of the database then importing all the data

For me the first lines look like this

and the last look like this

Now looking at the instance as a whole we can see the imported database

and here I am displaying geographical information through QGIS to get an idea of the data and ensure that it appears to be all correct.

    SUMMARY


There are quite a lot of tutorials online on how to do this but most seem to skip over some details - I've tried to be as accurate as possible but depending on you setup there may be differences. Nonetheless this is an extremely important task to perform so worth practicing to get right.

MS Access Function : Print to excel spreadsheet field definitions of all tables in a database

This places all tables and fields into an excel file on a single worksheet as a single table.

Public Function TableDef()
Dim def As TableDef
Dim wb As Object
Dim xL As Object
Dim lngRow As Long
Dim f As Field
Set xL = CreateObject("Excel.Application")
xL.Visible = True
Set wb = xL.workbooks.Add
lngRow = 2
For Each def In CurrentDb.TableDefs
For Each f In def.Fields
With wb.sheets("Sheet1")
.Range("A" & lngRow).Value = def.Name
.Range("B" & lngRow).Value = f.Name
.Range("C" & lngRow).Value = f.Type
.Range("D" & lngRow).Value = f.Size
.Range("E" & lngRow).Value = f.Required
lngRow = lngRow + 1
End With
Next
Next
End Function

MS Access Function : Loop through tables and export to csv

A function that will loop through an access database and export all tables to csv and xls.

Useful for subsequent import through QGIS into Postgres.

Public Function ExportAll()
Dim obj As AccessObject, dbs As Object
Dim strFolder As String
strFolder = "c:\"
Set dbs = Application.CurrentData
For Each obj In dbs.AllTables
If Left(obj.Name, 4) <> "MSys" Then
DoCmd.TransferText acExportDelim, , obj.Name, strFolder & obj.Name & ".csv", True
DoCmd.TransferSpreadsheet acExport, acSpreadsheetTypeExcel9, obj.Name, strFolder & obj.Name & ".xls", True
End If
Next obj
End Function

QGIS and PostGIS : Identifying direction of a vector

If using the dijkstra function with direction turned on it is important to identify the order in which the nodes of a vector line have been digitised. This is called the direction, dijkstra can use this with a reverse_cost attribute to handicap wrong movement along lines to such an extent that the correct path can be calculated around things like roundabouts.

Here is an example of the roundabout in Straiton in Edinburgh just North of the A720 bypass. While some of the lines have a correct anti clockwise orienation clearly some have been incorrectly digitised.

First we can see this by displaying the network in QGIS but using the styling to arrow the direction.

The function that can be used to reverse such inaccuracies if you can’t resort to buying a correct dataset try ST_REVERSE

017 Postgres command line : psql : Notices

RAISE NOTICE can provide the same function as Message Box in VBA ie you can use it to comment on the progress of a script. RAISE NOTICE is not supported by SQL so you can’t place it in scripts containing SQL they need to be in plpgsql scripts. This isn’t too much of a hassle as the way I am working at the moment I am calling the SQL anyway from plpgsql so I can place my message boxes in there.

No VBA Ok buttons.

CREATE OR REPLACE FUNCTION noticeexample() returns void as $$
BEGIN
RAISE NOTICE 'ONE FINE DAY IN THE MIDDLE OF THE NIGHT';
END;
$$
LANGUAGE PLPGSQL;

016 Postgres command line : psql : Strip out the Z coordinate from a geometry field

When creating a topology the geometry field cannot contain a Z coordinate.

OK but the Ordnance Survey Open Data highways layers containse a Z coordinate. Previously I had stripped this out using the latest version of QGIS which has a tick box in the front end that allows for import stripping of the z coordinate in the process. If you don’t have access to the latest QGIS version how can you strip out the z coordinates.

ST_FORCE2D

ALTER TABLE public.nuroadlink ADD COLUMN geom2(multilinestring,27700);
UPDATE public.nuroadlink SET geom2 = ST_FORCE2D(public.nuroadlink.geom);
ALTER TABLE public.nuroadlink drop column geom;
ALTER TABLE public.nuroadlink RENAME COLUMN geom2 TO geom;

015 Postgres command line : psql : Create functions and then script those functions

I had assumed after I had created a working SQL Script I would just be able to wrap the whole thing easily into a function and then bang it would be off to the races.
My script really needed to be run in order and for some as yet undefined reason I was getting particular errors where a table would be created and then a following query would add or alter that table. It looked like the second query was trying to adapt the table prior to its creation with an inevitable error.

I managed to get it working by making each SQL Query a function and then scripting the functions consecutively in a separate function using the PERFORM instruction.

I incorporate into this the check_function_bodies switch which just allows the creation of sql referring to objects that may not be in existence yet.

BEGIN;
SET LOCAL check_function_bodies TO FALSE;
CREATE OR REPLACE FUNCTION query01() returns void as $$
CREATE TABLE t001start 
(
pkid serial primary key,
geompkidt001 geometry(point,27700)
);
$$ LANGUAGE SQL;
CREATE OR REPLACE FUNCTION query02() returns void as $$
CREATE TABLE t002end 
(
pkid serial primary key,
geompkidt002 geometry(point,27700)
);
$$ LANGUAGE SQL;
COMMIT;

And then subsequently I create a function that runs the functions.

CREATE OR REPLACE FUNCTION runallthequeries() 
returns text as
$BODY$
BEGIN
PERFORM query01();
PERFORM query02();
RETURN 'process end';
END;
$BODY$
LANGUAGE plpgsql;

014 Postgres command line : psql : Create SQL function referring to a table or column that does not yet exist

I was trying to write a script that would allow me to measure distances to schools and my original script gradually built up tables that were subsequently deleted. Worked fine in one big sql script but when I tried to convert this into a function so that it could be more easily stored with the database I kept on getting error messages stating that it was not possible to create sql that referred to objects that did not exist. Postgres validates functions and will at default prevent creation of functions containing SQL that refers to objects not yet in existence.

Postgres does not however save dependencies for code in the function body. So although once the function is created the tables and views can be dropped (and the function still exists) in default you need a set of tables in place with default settings before the function can be created. One workaround would be to create dummy tables and views in advance and later drop them but this if often clunky and awkward. Luckily this validation can be turned off.

BEGIN;
SET LOCAL check_function_bodies TO FALSE;
CREATE or REPLACE FUNCTION examplefunction() Returns void AS $$
  CREATE TABLE t001 (pkid serial primary key, field1 varchar(20));
$$ LANGUAGE sql;
COMMIT;

Documentation says

check_function_bodies (boolean)

This parameter is normally on. When set to off, it disables validation of the function body string during CREATE FUNCTION. Disabling validation avoids side effects of the validation process and avoids false positives due to problems such as forward references. Set this parameter to off before loading functions on behalf of other users; pg_dump does so automatically.

see here
Documentation

Totally invaluable when you write scripts like I do.

013 Postgres command line : psql : Using ST_Within function to build junction tables to compare 2 separate polygon tables

First off let us create a new database to hold our examples in.

CREATE DATABASE stwithindb;

Now add the postgis extension.

Lets create two tables one called fields and one called plots

CREATE TABLE
t00001fields
(
pkid serial primary key,
fieldname varchar(50),
geom geometry(polygon,27700)
)
;
CREATE TABLE
t00002Plots
(
pkid serial primary key,
plotname varchar(50),
geom geometry(polygon,27700)
)
;

Now lets go to QGIS connect to the PostGIS instance add the tables and create some test data manually.

Here I have added fields in green with bold number labels and plots in brown with smaller number labelling. The numbers represent the pkid fields.

Now here I can quickly run a query to identify the plots that are in fields

SELECT t00002plots.pkid
FROM
t00002plots,
t00001fields
WHERE 
ST_WITHIN(PUBLIC.T00002PLOTS.GEOM, PUBLIC.T00001FIELDS.GEOM);

And it correctly identifies that plot 1 is within the fields layer.

But what would be great in an application is to have some kind of junction table that individual master records could display their children on. For this we need a junction table that links between the field and plots table showing the pkids from each.

SELECT t00002plots.pkid as Plotspkid,t00001fields.pkid as Fieldspkid
FROM
t00002plots,
t00001fields
WHERE 
ST_WITHIN(PUBLIC.T00002PLOTS.GEOM, PUBLIC.T00001FIELDS.GEOM);

Now I will move plot 2 into field 3 and rerun the above.

The layer now looks like

and running the former query we get.

Now its possible to either create a junction table to hold this information..

eg

CREATE TABLE t00010fieldplotjunction AS 
SELECT t00002plots.pkid as Plotspkid,t00001fields.pkid as Fieldspkid
FROM
t00002plots,
t00001fields
WHERE 
ST_WITHIN(PUBLIC.T00002PLOTS.GEOM, PUBLIC.T00001FIELDS.GEOM);

or we can create a view that will constantly calculate this everytime it is seen

CREATE VIEW v001FieldPlotJunction AS
SELECT t00002plots.pkid as Plotspkid,t00001fields.pkid as Fieldspkid
FROM
t00002plots,
t00001fields
WHERE 
ST_WITHIN(PUBLIC.T00002PLOTS.GEOM, PUBLIC.T00001FIELDS.GEOM);

Now if I add a few more plots and fields and then pull up the view we shall see that everything has been adjusted

and running the view we now get

In some circumstances this calculation may be expensive so we may wish to run and create a junction table overnight other times we may be happy to do it fully dynamically. Of course in a front end you could query and filter such that only one record was compared against the fields plot at anytime. Very useful nonetheless.

Extraction Transformation and Load (ETL) – some thoughts on a large IT transfer project

In 2017 I was involved in an important work project to transfer all the records in a legacy system that was being deprecated by the vendor into another maintained system. We were in some ways fortunate because both systems had been designed by a single company and they were encouraging us to transfer. We had delayed transfer for several years already but were aware that we now had to move. The vendor did have some tools in place , had staff dedicated to such transfers and were offering favorable consultancy rates. The amount of data was not horrendous in computing terms but they were far far beyond the remit of the ability to cope with any sort of manual data correction and the system was an absolute core system upon which several departments completely depended. These were systems that all departments are in from the moment they start the work day to the end. Generally its unusual if they are down for more than 5 minutes in a month, all work pretty much stops when they stop and in no circumstances could they be down for more than a day without special dispensation and coordination to indicate to manage customer expectations.

The whole project was a success although it was challenging. Here is an outline of the steps we took. As ever order here is important in most of the steps.

Step
Inform managers of all involved sections and ensure they are on board – identify and ring fence budget

Step
Appoint project manager on vendor and client side
draw together team to perform transformation.

Step
Draft time table creation of how long it will take putting in place planning for tutorials on systems and consultancy.

Step
Request managers to put forward staff on all sides willing to be involved

Step
Identify any omissions in knowledge and start to identify how this can be remedied. Kick off and complete acquisition of said staff.

Step
Meeting with lead staff to confirm buy in. Request buy in from staff including ring fencing of holidays etc.. to ensure key staff are available at required times.

Step
Set up test systems that all individuals have access to and ensure that the old and new systems can be viewed simultaneously by individuals. Ensure that the domain specialists can identify processes that will be mirrored from the old system to the new system

Step
Give DBAs or those that will be doing data transfer access to databases of source so that they can start thinking of how they can pull out information.

Step
Training for all individuals concerned in new systems.

Step
In new system start tasking individuals with how they are going to do the simple processes – eg register a record approve a record alter a record and get reports out. If possible allow new champions to start to define things like reports.

Step
Start making up any new lookup fields compared with old lookups and also start tasking individuals with creation of reports and letter that will need to be done.

Step
Start mapping the data from old system to new system – excel spreadsheets can be used for this that show the data going from the old system and what fields they are going to go into in the new system. Divide this task up between domain users – this step needs to be done after old and new systems are on domain users machines. As part of this the applications in question should expose if possible the table and field names of the source and target fields. With the systems we were involved in this was possible both for the old and new systems.

For each form on the two systems try to identify the below

Source table.field Target table.field

Also get them to map the lookup table values if direct transfer is not possible or if alias id are used in these lookups.

Source table.field.value=Equivalent.Target table.field.value

Step
Give both mapping documents to the ETL people to allow them to start writing the queries. It is unlikely that there will be a straight transfer across from table to table. While it would be expected that field and table names will be completely different it will be expected that table structure will in certain places be different in this respect it would be good to have a really nice schema diagram of both source and target.

Step
Allow data individuals to write scripts that can be run live against present initial system – if necessary doesn’t need to be live live could copy every night and then perform on 1 day old database backend – which is what we did. This means work can go on in old system and then at a touch of a button.

Encourage DBAs to be able to run these scripts every day to ensure that running them for go live is absolutely no issue. Our scripts only took about half an hour to run so this wasn’t an issue. I was personally involved in writing the SQL for those and I had systems in place to cross tab the amount coming into each new table so I could see new records and information from the old system trickling manually into the system and then being transferred.

Step
Test data input into new system

Step
Check test data input into new system with reference to domain users.

Step
Confirm go live date ensure staff available for issues

Step
Go live to production and start all new procedures ensure staff technical and domain key players on hand to make flexible solutions to things

Step
Project review on going maintenance and improvement of new system

Step
After suitable time turn off of old system if possible.

012 Postgres command line : psql : Run sql from a table

I wanted to be able to run thousands of queries or hundreds from Postgres like I can in MS Access this didn’t turn out to be too difficult.
Here’s something that works firstly lets create a new database

CREATE DATABASE sqlloopdb;

You will then need to connect to the database.

Next I will create 2 tables with; One table to be called t001sqltarget – this is the table we shall change with queries. One table called t002sqlrun – this will contain queries that we will run.

Please note the field names are important as well but I will let you study them in the code.

I then have 4 inserts that place valid SQL strings into the field sqltorun.

CREATE TABLE t001sqltarget (pkid serial primary key, fieldforupdate varchar(1));
CREATE TABLE t002sqlrun (pkid serial primary key, sqltorun varchar(1000));
INSERT INTO t002sqlrun(sqltorun) values ('INSERT INTO t001sqltarget(fieldforupdate) values (1);');
INSERT INTO t002sqlrun(sqltorun) values ('INSERT INTO t001sqltarget(fieldforupdate) values (2);');
INSERT INTO t002sqlrun(sqltorun) values ('INSERT INTO t001sqltarget(fieldforupdate) values (3);');
INSERT INTO t002sqlrun(sqltorun) values ('INSERT INTO t001sqltarget(fieldforupdate) values (4);');

First lets run the above and see what we have. Below you can see that I create the database then connect to it before opening the editor from which I run the above code I then take a look at the tables in the database and run a select to return all the records within the t001sqltarget table of which there are none.

Now lets run the following code and then take a look at t001sqltarget.

DO
LANGUAGE plpgsql
$$
DECLARE
stmt text;
BEGIN
FOR stmt IN
SELECT sqltorun FROM t002sqlrun
LOOP
EXECUTE stmt;
END LOOP;
END;
$$;

And after running there are 4 lines in the table

Every time I run the Do code four more records will be added to this table. Any SQL could be included in t002sqlrun and this is a nice demonstration of what I had previously able to do in MS Access and is massively powerful. It could be used for instance to calculate multiple measurements.

011 : Postgres amalgamate consecutive lines into a single line in a table

Here we take much of the work covered in post 010 and take the parts and user st_union to merge into a single record and place it in a table created by transforming a view into a table

Firstly go to your psql line and ensure that you are logged in with a username that you wish to be the owner of the table. In my case general

logging into edinburgh routing database

Now same measurement as before but this time we shall make a view out of the measurements then load that into a new table before deleting the view leaving us with the table with a combined measurement.

CREATE VIEW v001firstmeasurement AS SELECT seq,  id1 AS node, id2 AS edge, cost, geom, agg
  FROM pgr_dijkstra( 'SELECT id, source, target, st_length(geom) as cost FROM public.t01roadnetwork', 15883, 10967, false, false  ) as di
  JOIN public.t01roadnetwork pt ON di.id2 = pt.id ;

CREATE TABLE t003 as select sum(cost), st_union(geom) from v001firstmeasurement;

DROP VIEW v001firstmeasurement;

It is important in notepad to remove the blank spaces in the editor this looks as follows.

We then should then get some kind of confirmation that the view and table are created before the view is then dropped again. There might be a more efficient way of doing this but this was my first experiment. And we can go back to QGIS 3.4 and display the now single line in our project. Complete with now accurate measurement. It should be noted that if you were wanting to do multiple line measurements you would need to step out of the create statement and use an insert statement for all subsequent insertions as follows.
insert into t003(sum,st_union) select sum(cost),st_union(geom) from v001firstmeasurement;
This would allow you to do multiple measurments. I haven’t added up the measurement but it looks about right.

Blog theme gets upgraded to the 2016 WordPress standard

I had been using the 2010 WordPress standard theme as the basis for Round Up the Usual Suspects but decided it was time to upgrade. I decided to go for the 2016 WordPress standard theme as it is so well tested and with a relatively large back catalogue my primary concern was that I could port everything forward as easily as possible. I will be working on making it as user friendly as possible.

010 Postgres command line : psql : Getting started with pgrouting using open data from Ordnance Survey to identify and measure the shortest route between two points.

Objective here is to write a series of queries that can be used to measure the shortest distance between selected paired locations on a network such that the geometry of the routes can be calculated and displayed on a map.

For this particular tutorial you will need – QGIS 3 or higher and a version of Postgres I am using version 11.0 here (I have upgraded since my former posts). I believe this tutorial will work with previous versions but if you are following along now might be a good time to upgrade.

QGIS 3.4 or higher – needed as the Ordnance Survey road network geometry contains a z coordinate which will prevent the creation of the required geometry for measurement. QGIS 3 introduced the ability to save geometry excluding z coordinate. If you have a network without z coordinates you should not require this.

So let us first get the data. Here you tick the option in the top right hand corner – scroll to the bottom and submit your request after which you will be asked a few basic questions along with email address you wish the download to be sent to after a few minutes you should be sent the download link through your email – follow the instructions and you should be able to get the information

Ordnance Survey Open Data

The information you are downloading is a block framework for the whole of the uk. When you unzip the download into a folder you will see multiple files. We will be using a section of the national dataset relating to Edinburgh – NT. Choose the block or selection that you are interested in. More blocks may take more time however.

Open QGIS
Create a new project : eg EdinburghRouting.qgz
Load in your chosen network block : eg NT_RoadLink.shp

Select the layer you just loaded in : eg NT_RoadLink.shp

and navigate to the following in the menu settings
Layer / Save As

Fill out the Save Vector Layer as … dialog box
IMPORTANT – ensure within the Geometry section
Geometry type is set to LineString
Include z-dimension is unticked

Give the new file a name : eg ntosroutingnetwork.shp

Hit ok

Within the layer dialog of QGIS your new layer should appear you can now remove the for NT_RoadLink shape file from the project

Next go to your version of PostgreSQL and using a superuser account create a new database : eg edinburghrouting

I would suggest you use lower casing as well

As a superuser ensure you add the postgis and pgrouting extensions.

Next I set up the following connection between the QGIS project and PostgreSQL

Personal tastes may vary but I like like to select
Also list tables with no geometry
Allow saving/loading QGIS projects in the database

OK the selection and you should now have a connection to the new database you just created.

QGIS has an excellent dbmanager window which we will use to load our new shape file which excludes the z layer into the new database we created in PostgreSQL

Ensuring that you have a connection to your localpostgis database hit the

ImportLayerFile

Here I load the information into a new table t01roadnetwork

On pressing OK there will be delay after which if things go well you will receive the following message.

As ever it is good to check that things appear to be going well.
Add the layer to your project and determine approximately whether import was successful.

Next back in psql command line and in an editor we are going to run 4 queries
The first 2 add columns that are required in the shortest distance algorithm we shall use, the third will allow anyone to write an aggregation function to see the total cost of the route and the last creates a topology for the road network.

alter table public.t01roadnetwork add column source integer;
alter table public.t01roadnetwork add column target integer;
alter table public.t01roadnetwork add column agg smallint default 1;
select pgr_createTopology('public.t01roadnetwork', 0.0001, 'geom', 'id');

If things go correctly you should see the database engine start to create the topology and what I see is it gradually stepping through the creation process.

and on completion you should have something like the following:

A new table has been added to the edinburghrouting database and next step is to display the network and its vertices. In QGIS.

In QGIS we should see something like

The next thing that I like to do is to label the nodes so that for quick identification.

And look to the t01roadnetwork table and see if the columns are clear and present.

We are now ready to make a measurement. Here I choose the nodes 15883 and 10967

SELECT seq, id1 AS node, id2 AS edge, cost, geom , agg
  FROM pgr_dijkstra(
    'SELECT id, source, target, st_length(geom) as cost FROM public.t01roadnetwork',
    15883, 10967, false, false
  ) as di
  JOIN public.t01roadnetwork pt
  ON di.id2 = pt.id ;

Now we can load this as a new layer and then improve the symbology

Doing this we get.

It should be noted that the line you see is a collection of lines. In my next post I will go through and indicate how we can amalgamate that into a single line for storage in a table.

Congratulations if you have got this far you should be able to measure the shortest distance between any two points on a valid network by altering the numbers.

009 Postgres Command Line : psql : Altering the stated language – lets try Python

Given that on creation of a function it is a requirement to state the procedural language of calculation what happens if we try using Python?

Just so happens the calculation part of Python for Fahrenheit to Celsius syntatically is identical between SQL and Python sooo lets try this.

CREATE FUNCTION calcfp(integer) RETURNS integer AS 'SELECT ($1 - 32) * 5/9' LANGUAGE plpythonu RETURNS NULL ON NULL INPUT;

Yes they couldn’t just call python python it has to be plythonu.

This is what I got.So assuming I referred to Python correctly it would appear that I need to enable the use of python in postgres.

Given that I don’t know Python I am not going to install this as an extension but should you wish the following will be relevant;

Link to Create Language instruction

It has the following hightlighted instruction

Note: As of PostgreSQL 9.1, most procedural languages have been made into “extensions”, and should therefore be installed with CREATE EXTENSION not CREATE LANGUAGE. Direct use of CREATE LANGUAGE should now be confined to extension installation scripts. If you have a “bare” language in your database, perhaps as a result of an upgrade, you can convert it to an extension using CREATE EXTENSION langname FROM unpackage