Tag Archives: transact sql

Data Warehouse, Database, ETL, SQL Server, Transact-Sql

The INSERT statement and Column Defaults in Sql Server

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When you INSERT into a table which has a column with a default value defined, and you omit that column from your statement, what will happen? The default will be written. What if you write an explicit Null (and the column is nullable)? In nearly all cases the Null is written.

You may not want this – it’s one of the cases where it might be nice if there were more than one type of Null, as some people advocated in the early days. Then we could distinguish a “known unknown” (© D. Rumsfeld) Continue reading The INSERT statement and Column Defaults in Sql Server →

SQL, SQL Server, Transact-Sql

Complex T-Sql Column Expressions? You must try this!

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There’s an outstanding video by Kendra Little called “5 T-Sql Features You’re Missing Out On” which you can reach from my Links (Topical) page under “Database > Transact-Sql”. It describes a special way of using the CROSS APPLY statement in T-SQL. This is a technique that can change the way you write Sql, or at least it can in cases where you have an expression that is used in several columns of a SELECT statement. Continue reading Complex T-Sql Column Expressions? You must try this! →

Agile, Change Management, Data Warehouse, Database, SQL Server, Tools, Transact-Sql

“Test-First” Database Development (2)

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I’ve made additions and changes to the GitHub repository for “Test First” development of the database schema. All procedure names will now start with “Test”, so that they’re easier to find in Object Explorer and Intellisense. I’ve added a “TestHeader” stored procedure. You can put this at the top of your TDD script and it’ll add the date/time, database user, Sql Server version etc., to your results.

The spObjectExists procedure has been replaced by TestObjectExists, with the following signature:
CREATE PROCEDURE [dbo].[TestObjectExists]
@i_ObjectType sysname
,@i_ObjectName sysname = Null
,@i_ParentSchemaName sysname = Null --not needed if testing schema's existence
,@i_DbName sysname = Null
AS Continue reading “Test-First” Database Development (2) →

Agile, Change Management, Data Warehouse, Database, SQL Server, Tools, Transact-Sql

“Test-First” Database Development (1)

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I’m looking at the practicalities of using Continuous Delivery/Agile techniques where the database is a “high scale” project in Agile terms, and therefore relatively difficult (for more detail about this Agile terminology refer to Scott Ambler’s writings).

As well as thinking about the big issues, I want to start putting together some of the pieces to make it work. I’m doing this in Sql Server 2014 Transact-Sql. I’ve started with automated testing of reporting procedures. There may be utilities that can do this; finding suitable tools is part of the research. It still seems worthwhile having alternatives in Transact-Sql if possible. There’s no purchase or installation to approve, and the code is easy to understand and to edit. Continue reading “Test-First” Database Development (1) →

Data Warehouse, Database, ETL, SQL, SQL Server, Transact-Sql

Sql Server Collation Cheat Sheet

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This post is not written for an architect or DBA who has to choose a collation and wants an in-depth explanation, but for a developer (perhaps one with an error to fix) who needs a primer on the subject.

Put very simply, collations have to do with languages and with the rules used to compare characters. This is relevant in joins and sorting. You might think that a collation ought to be specified for the query; that in your sql statement you should determine the rules to use for comparing values. You can do that (although you’ll set it at column, not query level), but the columns in the tables have a collation property which is what the query uses by default. This is a convenience as it standardises comparisons and saves you having to specify the rules over and over again. It’s when the two conflict that you have an error which may make it necessary to override one or more default collations. Continue reading Sql Server Collation Cheat Sheet →

Data Warehouse, Database, ETL, SQL, SQL Server, Tools, Transact-Sql

OPENROWSET and BULK INSERT (3)

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This is the promised post about using a Powershell script to inspect large files. It won’t be possible to open a very large file in Excel of course, and some text readers may struggle under the weight of data. This script is an alternative that runs under most if not all versions of Windows, and doesn’t need an installation or a licence. Continue reading OPENROWSET and BULK INSERT (3) →

Data Warehouse, Database, ETL, Transact-Sql

OPENROWSET and BULK INSERT (2)

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As a data warehouse developer you’ll probably have to load big files. Even if you’re not responsible for loads in PROD, you may well have to import data into the DEV database. There’s often an expectation that this shouldn’t take long, so if you hit any problems you could come under time pressure.

A toolkit and a methodical approach can help you to grind out a predictable result every time. I hope these notes may be some help. Continue reading OPENROWSET and BULK INSERT (2) →

Data Warehouse, Performance, SQL Server

Stored Procedure Performance – What You Can Do

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There are lots of things you can do to address stored procedure performance issues in Sql Server (this is based on version 2014 which is what I’m currently working in). In fact, there are so many techniques that they seemed worth listing in a blog. Of course, correct indexing is fundamental; I’m assuming you’ve looked at that already. What is listed below would be more appropriate for problems such as execution plans being compiled with specific parameters and not working well when other parameters are passed in. There’s no detail here though: please bear in mind that some of the commands listed are well-known to be buggy. You’ll need to Google for more information on issues and trade-offs. Continue reading Stored Procedure Performance – What You Can Do →

Database, Oracle, Rants, SQL, SQL Server, Transact-Sql

Just Say No… to Day Number Functions

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In a Mental Status Examination a psychiatrist will assess the patient, often to decide whether they should be admitted to hospital. Quoting the article linked above, “Orientation is assessed by asking the patient … what time it is (time, day, date)”. So the patient is asked what day of the week it is.

What if the psychiatrist were to ask instead, “What is the number of today, based upon where it falls among the days of the week”? That might indicate that the doctor himself was under too much pressure and needed to take some time off, and it would also be quite unfair to the patient. We need to know what day it is, we often need to know when the week starts or finishes, but we don’t usually ask ourselves what number the day is.

There are database functions that provide the day number: in Sql Server it’s: SELECT DATEPART(weekday, SYSDATETIME()), and in Oracle it would be TO_CHAR('d', SYSDATE), which you can cast to a number of course. Do we ever need to know it? Continue reading Just Say No… to Day Number Functions →

SQL Server, Transact-Sql

Sequential uniqueidentifiers in Sql Server Tables

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I’ve just come across this feature of Sql Server which apparently has been around since Sql 2008 (code in this example tested in Sql Server 2014). There might be good reasons for wanting to use a GUID in a clustered primary key, but since the key is random there may be issues later on with INSERTs into the table.  Continue reading Sequential uniqueidentifiers in Sql Server Tables →