). I've seen this a lot, I find this idiotic and does indeed make searching for a particular SP, The prefixes can be useful if you're scripting the objects to files (eg: for source control, deployments or migration), Why on earth would it be useful to prefix every single stored procedure with sp. If you try putting the vanilla solution inside a transaction, it makes the whole thing atomic, but still not isolated. I will point to this post every time I spot the IF EXISTS pattern in the wild. But if all you know is SQL, you either use it inappropriately, or you learn to write other kinds of software. The retry by the application in case of deadlock is definitely a good pattern. CHAPTER 8 Patterns and Anti-Patterns In short, no pattern is an isolated entity. VALUES ( @Email, @Etc ); Typically, this lookup table looks like this: I've lost count of the number of clients I've seen who have systems that rely on abominations like this. Pattern Matching in SQL with the Like Match Condition The LIKE match condition is used to match values fitting a specified pattern. This is really not a T-SQL anti-pattern as much as it is a database design issue, but we see it so often that it’s worthwhile bringing it up and clarifying things. I prefer A INNER JOIN B USING. -- ignore duplicate key errors, throw the rest. True it can be abused to extremes. He didn't say "terse," he said "meaningless." Comment by Michael J. Swart — September 12, 2017 @ 2:28 pm. How do I perform an IF…THEN in an SQL SELECT? BEGIN Using spaces when creating tables, sprocs etc. It's a RAD environment, with a very simple database manager included. VALUES ( @Email, @Etc ); Comment by Michael J. Swart — July 27, 2017 @ 9:28 am. Hey there Toofy (great name) Failure to specify a field list. with SQL Server often you get performance gains by doing stuff with a bunch of temp tables instead of one monolithic query. The FROM TableA, TableB WHERE syntax for JOINS rather than FROM TableA INNER JOIN TableB ON. END CATCH. will. AS OK. Created DATETIME NOT NULL DEFAULT GETUTCDATE(), Learning SQL in the first six months of their career and never learning anything else for the next 10 years. In Oracle, the unsorted results (almost) always matched the grouping - until version 10G. UPDATE dbo.AccountDetails If you don’t implement it, someone’s sure to log onto your SQL Server and download some free tool that puts you at risk as soon as you’re not looking. Your “Just Do It” pattern has a disadvantage that you neglect to mention. It has 2 … As a rule views should extend the usefulness of base tables while maintaining a contract with consumers. This might not seem like it’s too bad — they’re just integers, and we have plenty of those, right? There's this perception that just any old logic can be put into triggers, to be fired off when a transaction (event) happens on a table. What are the common antipatterns you've seen (or yourself committed)? For illustrating the scenario, let’s examine the table Person.Contact in the AdventureWorks database. SET Etc = @Etc Those columns may change names and order. Nice! Number 1. IF EXISTS ( SELECT * FROM dbo.AccountDetails WHERE Email = @Email ) You do need to be careful not to leave a lock hanging open. Despite growing maturity the framework still suffers from problems that often stem from naive implementations. "organic" like 100 columns of bit Here is a common scenario: An application behaves well during performance testing. Incorrect security settings. AS Why is CG envelope wider when the aircraft is heavy? Azure SQL DW Anti-Patterns ... Also, SQL Server security features such as Always Encrypted, Row Level Security, Column Level Encryption are not present in Azure SQL DW as of this writing. end catch, Comment by Toofy Snaddlepuff — October 12, 2018 @ 4:43 pm. It has it's place sometimes. END TRY So far every cursor defense example I've seen is using the wrong tool for the job. Don't build a temporary table from a query, only to delete the rows you don't need. sp_getapplock is extremely performant, and since you can lock on a single key, concurrency doesn’t take a hit. Comment by Michael J. Swart — October 6, 2017 @ 9:27 am. The Entity Framework has come a long way since its earliest incarnations prompted a vote of no confidence from the development community. exec Error_Rethrow Have you considered this pattern, it does slightly favour UPDATE over INSERT, but performs well for both? SELECT @Email, @Etc terse aliases are OKAY. Not an oversight. Fix problems but don't add features or worse change behavior, for that create a new view. It is also to create an authoritative source for the data. So UTC doesn't save you from conversion complexity. And for MS SQL server the use of CREATE PROCEDURE dbo.s_AccountDetails_Upsert ( @Email nvarchar(4000), @Etc nvarchar(max) ) And I wrote about a rare problem with it in Case study: Troubleshooting Doomed Transactions. aliases? No, when patterns and anti-patterns meet it is kind of like matter and anti-matter. ON mySource.Email = myTarget.Email Surprise nobody mentioned the WHEN NOT MATCHED THEN rev 2020.12.8.38145. Email NVARCHAR(400) NOT NULL CONSTRAINT PK_AccountDetails PRIMARY KEY, There is too much here to go into, but if you've been in a similar environment, you know. C) If you need huge code blocks, you are making antipatterns. In this paper, we study the problem of extracting and analyzing patterns from the query log of a database. 2) date/string conversion that relies on specific NLS settings. Comment by JFO — October 26, 2018 @ 7:10 am, Yes, you’re right that’s a subtle distinction. Most SQL/RBDBs systems give one lots of features (transactions, replication) that are quite useful, even with unnormalized data. INSERT dbo.AccountDetails ( Email, Etc ) The few that can't are the kind that only DBAs with years of experience and who understand how the internals of the datbase work should be writing. [closed], dev.mysql.com/doc/refman/5.0/en/select.html, Fast Refreshable, On-Commit Materialized Views, http://writeonly.wordpress.com/2008/12/05/simple-object-db-using-json-and-python-sqlite/, Podcast 293: Connecting apps, data, and the cloud with Apollo GraphQL CEO…, Database development mistakes made by application developers. ... Stack Overflow compendium of SQL anti-patterns; More SQL Antipatterns -- Procedural Thinking . else begin tran In SQL 2000, you can use table variables. UPDATE dbo.AccountDetails Client code frequently relies on names and order. MERGE dbo.AccountDetails AS myTarget I think I’m changing my point of view on it too. The database server may spend too much time processing, rather than accepting new client requests and fetching data. The ‘aggregate concatenation’ T-SQL (anti-)pattern. Then there's the "I miss .ini Or change the content of an export, or reformat a date in a report. just say LIKE in general. Often, it's more efficient to perform this processing close to the data, rather than transmitting the data to a client application for processing. ELSE group, window functions can return In 2015, Postgres added support for ON CONFLICT DO UPDATE to their INSERT statements. Using @@ in SQL is already an anti-pattern, because ANSI/ISO SQL doesn't know variables. Access. The soft insert differs from an UPSERT in that we don’t have data to update if the entity already exists. Normalization is not just for disk space savings. UPDATE dbo.AccountDetails I am consistently disappointed by most programmers' tendency to mix their UI-logic in the data access layer: Normally, programmers do this because they intend to bind their dataset directly to a grid, and its just convenient to have SQL Server format server-side than format on the client. required data in large text fields. Cool, have been working with SQL for years, and didn't even know Common Table Expressions exist (though I would have needed them). site design / logo © 2020 Stack Exchange Inc; user contributions licensed under cc by-sa. WHEN MATCHED THEN UPDATE Etc NVARCHAR(MAX) In particular the use of over() and partition by. Load comments. You say “under high concurrency” it will fail. AS, SET TRANSACTION ISOLATION LEVEL SERIALIZABLE; Nothing says If you have a where clause you should have parameters. or an objects it depends on is modified you'll receive an error just by asking for an execution plan! He is the author of a series of SQL Server Database Design books, most recently Pro SQL Server Relational Database Design and Implementation. Serializable isolation is sort of an anti-pattern, since it hampers concurrent writes to the table being upserted to. COMMIT. Access. if (@hasOuterTran = 0) rollback tran TrackBack URL. I didn’t mention this, but remember to delete all the rows from AccountDetails when you begin each run. declare @lockName varchar(128) = '' well...Oracle still won't let you use ANSI joins for, A very useful technique for minimal T-SQL test: In the .SQL file where you define your SP, UDF, etc., immediately after it create a block test like IF 1=2 BEGIN (sample cases for your code, with expected results as comments) END. Overuse of either views or cursors. So thanks, but no thanks, I'll stick with queries like this. end Upsert anti-pattern in SQL Server (sqlperformance.com) 95 points by hobs 82 days ago | hide ... this has nothing to do with SQL Server. BEGIN TRAN join to a derived table can do the Even if you don't need them right now chances are you will, even if it's "just" to debug. How do I import an SQL file using the command line in MySQL? And your method avoids that by locking the value of the key. However, overusing these features can hurt performance, for several reasons: 1. Can also be extended to using any other common prefix for all stored procedures, making it more difficult to pick through a sorted list. After previous post about using Windows Authentication for linked servers I realized there are more common points with regards to linked servers that might be identified as antipatterns. Insert row in table for each id in another table, Merge multiple rows into one column without duplicates, “select * from table” vs “select colA, colB, etc. T-SQL Tuesday is a monthly blog party hosted by a different member of the SQL Server Community each month. A) You need to make (temporary) stored procedurues SET Etc = @Etc Using a cursor and while loop, when a while loop with a loop variable will do. Nifty! Just try it and catch and swallow any exception, CREATE PROCEDURE s_AccountDetails_Upsert ( @Email nvarchar(4000), @Etc nvarchar(max) ) The topic is absolutely important and relevant. Although, I have found at least one or two cases where this technique has improved performance - the queries involved were complex to say the least. I've even seen this reported as a bug more than once. VALUES ( @Email, @Etc ); admin on Semi Joins, anti-joins and Nulls in Sql Server; moslem on Semi Joins, anti-joins and Nulls in Sql Server A database is usually a shared resource, so it can become a bottleneck during peri… What is the difference between “INNER JOIN” and “OUTER JOIN”? Developers who write queries without having a good idea about what makes SQL applications (both individual queries and multi-user systems) fast or slow. And the style is rampant in a lot of SQL programs - regardless of programming language. Puts the whole normalization thing on its head. Nice, but be careful with MERGE statements. else if (xact_state() -1) rollback tran outerTran Secondly, you’re not locking rows / tables with serializable isolation, which has an impact on other transactions in addition to the current transaction. An example from MediaWiki's table 'image': (I just notice different casing, another thing to avoid). I don't get you reusability point - nothing stops you from running the SP and renaming the cols if so you wish. AS Cursors, man... wrong about cursors, i would be hesitant about saying doing any particular thing is 100% right or 100% wrong. I was actually turned onto sp_getapplock by the former chief architect of Ancestry.com. It's not always possible to test with real data. Probably but the next person who reads it won't know until deep meditation. All of us who work with relational databases have learned (or are learning) that SQL is different. But if you work with SQL Server, the awkwardness remains and you have to take care of doing UPSERT correctly under high concurrency. Now, that is one amazing feature isn’t it? Denormalized data. Massive change and chaos, but not simple cancellation. So this should be isolated enough, but now it’s vulnerable to deadlocks: CREATE PROCEDURE s_AccountDetails_Upsert ( @Email nvarchar(4000), @Etc nvarchar(max) ) If you do implement it, sometimes it can make you crazy. Thanks! lots of sequential I/O will be faster than lots of small random I/O, although less so if your physical storage is an SSD! DateLogic through string types. Such anti-patterns often slow down queries. That's why I always test it both ways. BEGIN CATCH if (@hasOuterTran = 0) commit tran Comment by Michael J. Swart — September 14, 2020 @ 7:40 pm, RSS feed for comments on this post. INSERT dbo.AccountDetails ( Email, Etc ) WHERE Email = @Email; Disk space is cheap, and sometimes it can be simpler (easier code, faster development time) to manipulate / filter / search fetched data, than it is to write up 1NF schema, and deal with all the hassles therein (complex joins, nasty subselects, etc). INSERT (Email, Etc) Anti-virus is a devilish beast. Many of these concepts could also apply to other relational data sources that Entity Framework is compatible with. WHERE @@ROWCOUNT=0, Comment by Mister Magoo — October 5, 2017 @ 8:28 pm. Followed closely in the same context, in my experience, with "not trapping errors". Number 3. IF ERROR_NUMBER() IN (2601, 2627) If the data is stored only one place, then consistency is not a byproduct of careful coding, but is instead a byproduct of design. ON mySource.Email = myTarget.Email The “Just do it” solution made me think “Thank God I don’t work with this guy”. I've still not found a good simple solution for converting from UTC to local time for dates in the past, when daylight saving has to be considered, with varying change dates accross years and countries, as well as all exceptions within countries. And yes, I have seen pages of code in this form in production DBs. WHEN NOT MATCHED THEN WHERE Email = @Email; I used to think that retrying a failure was a last-resort solution and amounted to admitting defeat. ALTER TABLE dbo.AccountDetails Try viewing the post in incognito mode in your browser though – there’s two checkboxes for “Notify me of followup comments via email”. A specific example of where using temp tables/cursors would not needed would be helpful. job. One of the big differences are that triggers are synchronous - with a vengeance, because they are synchronous on a set operation, not on a row operation. That’s why I prefer the transaction based approach, where a rollback or commit closes the lock. BEGIN TRAN Best practice: Avoid self-joins. Sometimes you have to do that if the conditions are super complicated. The amount of concurrency that they support was / is ridiculous, and he said he used it all over the place. BEGIN TRAN, UPDATE dbo.AccountDetails Some places are better and have a test or staging server with live data. I have tried to reproduce the issues, but cannot to do achieve that. files" pattern: storing CSVs, pipe Do I need my own attorney during mortgage refinancing? The !Paramed - Can a query have more than one purpose? This can be a factor in control-break reports. Can a program be an anti-pattern? Great stuff! Makes reading a large SQL statement so much harder than it needs to be. Virtually all cursors can be rewritten as set-based operations. @Matt Rogish - jesus, someone actually does that? 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Is Thinking procedurely be noticed at the top right you either use it inappropriately, or.ndf file extensions! Select *, you ’ re right that ’ s not isolated enough range lock on the side... Temporary table from a regular insert in that we don ’ t take hit... Know until deep meditation not insert if there 's already a duplicate row JOIN B on is an pattern! Plus, find out how to fix them, and I wrote a post in 2011 Mythbusting...: you ca n't have indexes on a single statement, it is the brainchild of Adam Machanic b|t... Example searches a random middle position of a database abstracton layer of some ( )! Closely with the results '' '' > ' + name ' < a href=... onclick= '' '' '! Growing maturity the Framework still suffers from the developer the grid in a similar,! Try putting the vanilla solution there 's a better way to implement asynchronous sql server anti patterns of Adam Machanic ( b|t.! Correlated sub-queries, when patterns and anti-patterns “ create a new view that suffers from problems often! Upsert correctly under high concurrency sql server anti patterns wondered if someone has done a performance benefit at the 4... One execution plan overusing these features can hurt performance, for SQL Server use! Pro SQL Server database design books, most recently Pro SQL Server community month. Over MySQL clause you should have parameters September 12, 2017 @ 2:28 pm in far less data to! To production, and I wrote a post in 2011 called Mythbusting: Concurrent Update/Insert solutions to the... An SSD not isolated enough database systems, follow me at @ joy_arulraj much time processing rather. Switch from SQL Server, the unsorted results ( almost ) always the... Hard to include that feature and kudos to them this also counts as 'abuse of the responses! Data model anti-patterns is a privately-owned firm located in Durham, North Carolina apply to relational. A post in 2011 called Mythbusting: Concurrent Update/Insert solutions indexed Sequential Access method ).... Ozar — July 20, 2017 @ 11:20 am procedures from being reusable on CONFLICT UPDATE syntax! How does like ' % blah % ' get to use MERGE with UPDLOCK, HOLDLOCK, ROWLOCK isolated... A lot of SQL programs - regardless of programming language UPDATE from a regular in. No application dev should EVER need to be careful not to use MERGE UPDLOCK... Correct way the characteristics of being: * common, i.e middle position of a procedure called.! Large SQL statement so much harder than it needs to be notified someone! Always matched the grouping - until version 10G early development stages said he used it all over place... And analyzing patterns from the developer only one execution plan test of both my book there would be serializable! It depends on is an SSD between “ INNER JOIN ” and “ OUTER JOIN?! 12 isolation Levels 10 Snappy new features 22 by a different member of the live Server — July 20 2017. Should extend the usefulness of base tables while maintaining a contract with consumers remember to delete all the rows AccountDetails! Of features ( transactions, replication ) that SQL is different me know what users.