Some hand-matching of internal/external records may be needed even in an automated reconciliation. The matches will be stored in a database. Rules on matching can be enforced in the application, but there are often good reasons to place them in the database. In Sql Server, a filtered index (with a WHERE clause, in this case excluding Nulls) on the table can make this easier and more correct. Continue reading Simplify Reconciliation Code with Filtered Indexes
Category Archives: SQL
Forgotten Features of Sql Server
Well, not literally – these are features I tend to overlook because I don’t often need them. If you’re the same, this may be helpful. It isn’t a complete list (I’ve forgotten the others) but I’ll try to add to it as things come to mind. Continue reading Forgotten Features of Sql Server
Sql JOIN Cheat Sheet
Someone accidentally found my Sql Collation Cheat Sheet while searching for a “Sql JOIN Cheat Sheet” so I thought I’d knock out a post on the topic. Towards the end, you’ll find a script that demonstrates them. The script was run in Azure Sql. Some joins may be Microsoft extensions to the ANSI standard. Look at the documentation for fuller information.
When I was a beginner I had thought there was a deep meaning to the words “left” and “right”, as in LEFT OUTER JOIN. It was a mild let-down to find out that it only refers to placement of the table name in relation to the “JOIN” keyword; switching a LEFT OUTER to a RIGHT OUTER join defines the table named after the join keyword as the outer table. Continue reading Sql JOIN Cheat Sheet
Raising Errors in Transact-Sql
There seems to be quite a bit of confusion about the way errors should be raised in newer versions of Transact-Sql. The documentation for RAISERROR says: “New applications should use THROW instead.” It doesn’t say that RAISERROR is deprecated; when you look at the list of deprecated features what you find is that invoking RAISERROR without an error number is now deprecated, but it’s unclear whether the command itself will go. Continue reading Raising Errors in Transact-Sql
Sql Server CONTEXT_INFO with Numeric Values
A trigger takes no arguments but it is possible to use CONTEXT_INFO() to make 128 bytes of binary data values accessible to it. I wanted to provide an 8-byte (bigint) value from a sequence which the trigger would write to a primary key column.
Storing and retrieving a numeric value in CONTEXT_INFO is not difficult, but it’s another thing that doesn’t come up very often. For this type of problem I like to find concise explanations with source code so that I can get back to the main problem quickly. Once again my searches didn’t turn anything up so I’m trying to fill the gap with this post. Continue reading Sql Server CONTEXT_INFO with Numeric Values
Notes on the OVER Clause in Sql Server Ranking Functions
This article only deals with a couple of points so I’ll keep it short.
FIRST_VALUE, LAST_VALUE
FIRST_VALUE is a very useful ranking function and works predictably. LAST_VALUE is also useful but may give you surprises. You can ignore LAST_VALUE if you want, and just re-use FIRST_VALUE: Continue reading Notes on the OVER Clause in Sql Server Ranking Functions
Complex T-Sql Column Expressions? You must try this!
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!
Sql Server Collation Cheat Sheet
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
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)
Just Say No… to Day Number Functions
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
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