errors in database design

10 Dec errors in database design

comment on books and rate them after reading. consider which data is important to be tracked for changes/versioned. It should always be a timestamp type. Thus, we would avoid making changes in the database. Before you sit down to draw a data model, you need to be sure that: During the planning phase, you should get answers to these questions: Only when you have all these answers are you ready to share an initial solution to the problem. This is definitely a non-technical problem, but it is a major and common issue. People (myself included) do a lot of really stupid things, at times, in the name of “getting it done.”. And it is too good. scheduling bulk deletes at night, to avoid unnecessary table locks. You have a performance problem? This is definitely a non-technical problem, but it is a major and common issue. You’re completely aware of what your client does (i.e. If you want to learn to design databases, you should for sure have some theoretic background, like knowledge about database normal forms and transaction isolation levels. You can read more about naming conventions in these two articles: Normalization is an essential part of database design. I personally think it has helped me a lot when it comes to DB designing. But if they format it using bold font, like this: then it will take 24 characters to store while the user will see only 17 in the GUI. Any criticism is welcome. we must be able to restore the data without too much work. Do you think we missed something important? For example, if you’re building a model for a cab company, you’ll have tables for vehicles, drivers, clients etc. If you store a client’s name in two different places, you should make any changes (insert/update/delete) to both places at the same time. It happens. It seems PostgreSQL is not wise enough to select 30 newest records without sorting all 600,000 of them. You can read more about normalization in this article. if applicable, apply collation to columns and tables – see. Some are very common regardless of the business, e.g. But honestly, that’s usually not the case. It not only takes up additional disk space but it also greatly increases the chances of data integrity problems. There are multiple ways of achieving this goal: As usual, it is best to keep the proverbial golden mean. ), How will we name foreign keys? What names will be used for tables in the model? This is important, both for your schedule and for the client’s timeline. in single-language applications, always initialize the database with a proper locale. We all get excited when a new project starts and, going into it, everything looks great. For each customer, we’ll only have records for the attributes they have, and we’ll store the “attribute_value” for that attribute. user_account, role). Here is the model with book_comment type changed to text: There is a saying that “greatness is achieved, not given”. Smashing is proudly running on Netlify.. Fonts by Latinotype. Here is the final version of our bookstore model: If you have any questions or you need our help, you can contact us through A quick fix could save some time now and would probably work fine for a while, but it can turn into a real nightmare later. This is all great, and a great future will probably be the final result. Without a sequential key or a timestamp, there’s no way to know which data was inserted first. Separating frequently and infrequently used data into multiple tables is not the only way of dealing with high volume data. If the field will be plain-text in the GUI (customers can enter only unformatted comments) then it simply means that the field can store up to 1000 characters of text. In my opinion, we have a serious problem. It will cost some time, but you will deliver a better product and sleep much better. Yet we still have issues with poor datatype choices, the use… 4 n00b MySQL Mistakes Every Programmer Makes - DevOps.com - […] of the common database errors identified by Thomas Larock on the SQL Rockstar site is playing it safe by… While they hold UNIQUE values, they don’t make good primary keys. Luckily, it covers most characters used in all the world. (Most likely, it will be “id”. Then we will have a good chance to restore it and avert the loss. Writing documentation happens just before the project is closed — and just after we’re mentally done with that data model! If they enter a simple comment, like this: then it will take only 17 characters. Book description is likely to remain unchanged, so it is a good candidate to be cached. Managing time zones in date and datetime fields can be a serious issue in a multinational system. This will add data in sequential order to the primary key and provide optimal performance. You should find balance between security of data and simplicity of the model. The database design provider or advisor, which you pick up, should be neglect these rules. If you do this, have a really good reason. I’ve split the list of errors into two main groups: those that are non-technical in nature and those that are strictly technical. On the other hand, completed purchases are only kept as historical data. Accidental deletion of data. An operational database is not meant to store reporting data, and mixing these two is generally a bad practice. This issue also arises when we use UNIQUE real-world values (e.g. limiting length of text columns in the database is good in general, for security and performance reasons. However, when setting text field limits, you should always remember about text encoding. They are rarely updated or retrieved, so you can deal with longer access time to this table. Make sure you understand the details of your database driver. In this article, I’ve listed 24 different database design mistakes that you should try to avoid. But there are two traps here: We will illustrate this with a simple SQL query on French words: This is a result of sorting words letter-by-letter, left to right. in multi-language applications, initialize the database with some default locale, and for every place when sorting is available, decide which collation should be used in SQL queries: probably you should use collation specific to the language of the current user. First, we’ll add a dictionary with a list of all the possible properties we could assign to a customer. (E.g. Check the details of date and time data types in your database. ), there comes the second question – who did it? The database has eight tables and no data in it. Separate frequently updated data from frequently read data. The users must see the promotion date in their own time zone. But non-technical skills? Use them as alternate keys instead. Please tell us in the comments below. Most often we assume that sorting words in a language is as simple as sorting them letter by letter, according to the order of letters in the alphabet. The frequent updates slow down getting basic info of the user. tables in the database can have creation, and update timestamps, together with indication of users who created / modified rows. If you mean Christmas Eve midnight in your own time zone, you must say “December 24, 23.59 UTC” (or whatever your time zone is). If you want to learn to design databases, you should for sure have some theoretic background, like knowledge about database normal forms and transaction isolation levels. At the start, the project is still a blank page and you and your client are happy to begin working on something that will create a better future for both of you. Adam Evanovich lives in Iowa in the United States and frequently works on contract in various industries. But in other languages it may be possible. Database designing is crucial to high performance database system. Ask them to explain what you don’t understand. You can use the language/terminology your client uses. Will we use uppercase and lowercase letters, or just lowercase? Therefore, GUIDs seem like a great candidate for the primary key column. Error establishing a database connection is one of the most common errors that cause your site to temporarily be inaccessible is the database connection error. Note , the genius of a database is in its design . Do it as it should have been done, no matter what the current situation. Which tables will be the central tables in your model? In case of handling time zones the database must cooperate with application code. browse and search books by book title, description and author information. Suppose that we want to store some additional customer attributes. How do we check that? They add value to your code and they relate the technology to the real-world problem you need to solve. second, sorting letter-by-letter is sometimes wrong when accents come into play. be able to associate the fact of deleting the data with some URL in our access log. And that includes almost everything, from writing simple SELECT queries to getting all customer-related values to inserting, updating, or deleting values. Who damaged the data three months ago? For example, a table you query might have columns added or deleted, or their types might have changed. What does this mean? In fact, there are some situations where redundant data is desirable: In most cases, we shouldn’t use redundant data because: I hope that reading this article has given you some new insights and will encourage you to follow data modeling best practices. Now I will import this SQL into the PostgreSQL database. Right Way To Fix Common Errors In Database Design. 2006–2020.. When it comes to organizing data, I see the same mistakes in database design as I see in object design: Some developers like to turn everything into a … Criterion: Discuss how potential errors in the design and construction of a database can be avoided. For example, if you try to save the word “mother” in Chinese – 母親 – and your database encoding is UTF-8, then such a string will have 2 characters but 6 bytes on disk. Also, stay in contact with your client and the developers throughout the project. It is the same for performance – it is achieved by careful design of the database model, tuning of database parameters, and by optimizing queries run by the application on the database. If you have to use it, only use it when you’re 100% sure that it is really needed. To reduce the time spent on unexpected changes, you should: If you try to avoid making changes in your data model when you see a potential problem — or if you opt for a quick fix instead of doing it properly — you’ll pay for that sooner or later. To determine this, we need to: This will for sure take a lot of time and it does not have a big chance of success. (See Point 4 about naming conventions.). Time of events should always be logged in a standardized way, in one selected time zone, for example UTC, so that you could be able to order events from oldest to newest with no doubt. Design your programs to work when the database is not in the state you expect. It takes less than 70 milliseconds on my laptop. IT Solutions Zambia can design database solutions in both access and SQL or a combination of both with an Access front end and SQL back end on a SQL server. However, as you probably remember, “order” is a reserved word in SQL! You never know if or when you’ll need that extra info. Analyze that area and implement changes if they will improve the system’s quality and performance. Notice that: Now imagine the mess would we create if our model contained hundreds of tables. When you start the database design process, you’ll probably understand most of the main requirements. Of course, if you keep your database backed up regularly, you're going to be all right. Ever. So – language of content can affect ordering of records, and ignoring the language can lead to unexpected results when sorting data. Ideally, you’d know every detail: who works with the data, who makes changes, which reports are needed, when and why all of this happens. In the non-naming-convention example (the upper three tables), there are a few things that significantly impact readability: using both singular and plural forms in the table names; non-standardized primary key names (. There are a small number of mistakes in database design that causes subsequent misery to developers, managewrs, and DBAs alike. This will increase the readability of the whole model and simplify future work. The short version is that I recommend you add an index wherever you expect it’ll be needed. No list of mistakes is ever going to be exhaustive. Data backup When you design a database, you’re designing it to ensure it meets the needs of the business and the system that uses it. remember they will not always be used; the database may decide not to use an index if it estimates the cost of using it will be bigger that doing a sequential scan or some other operation, remember that using indexes comes at a cost –, consider non-default types of indexes if needed; consult your database manual if your index does not seem to be working well. Join our weekly newsletter to be notified about the latest posts. The “customer_attribute” table contains a list of all attributes, with values, for each customer. Using identity/guid columns as your only key First Normal Form dig this my work I haven't noticed any performance decrease. They tend to think normalization is the only way of designing. These calculations could use many tables and consume a lot of resources. We all get excited when a … Common Database Problems And Solutions. Before modeling, you should know: Compare part of a model that doesn't use naming conventions with the same part that does use naming conventions, as shown below: There are only a few tables here, but it’s still pretty obvious which model is easier to read. Everyone agrees that great database performance starts with great database design. EAV stands for entity-attribute-value. In some cases, we may want to denormalize our database. How do . Tutorial: Step by Step Database Design in SQL Published on February 22, 2015 February 22, 2015 • 348 Likes • 43 Comments The database development life cycle has a number of stages that are followed when developing database … And while it is importing, I will check time of execution of the previous query. Poor Naming Standards. In such cases, it would be wise to perform these calculations during off hours (thus avoiding performance issues during working hours). Why does it take longer? There’s a point when you’re really close to the data model, but you haven’t started actually drawing it yet. Storing the same data more than once in the database could impact data integrity. Skipping is only an option if 1) you have a really small project; 2) the tasks and goals are clear, and 3) you’re in a real hurry. This structure can be used to store additional data about anything in our model. The “customer” table is our entity, the “attribute” table is obviously our attribute, and the “attribute_value” table contains the value of that attribute for that customer. While we could store some aggregated numbers in our operational database, we should do this only when we truly need to. You should similarly optimize data which are frequently updated. Now we're entering the territory of a bigger problem. They will save you some time! Almost too good to be true. The project was in a rush because of the news that the US was planning to launch their own satellite soon – but I guess you won’t be in such a hurry. Current purchases are retrieved all the time: their status is updated, the customers often check info on their order. Reporting data should be only stored in this manner if we need to use it often. The Author. It’s not surprising to see these errors on the list. Then there are also other information in the user table, for example their basic info like login, password and full name. Obviously, if you don’t have technical skills, you won’t know how to do something. avoid using SQL and database engine-specific keywords as names; Oracle has the aforementioned limit of 4000 bytes for, Oracle will store CLOBs of size below 4 KB directly in the table, and such data will be accessible as quickly as any. Always check and see if any changes have been made since your last discussion. It’s definitely the best practice. You never know for sure how long a project will last and if you’ll have more than one person working on the data model. In a small database, like ours, it is not a very important matter indeed. The benefits are: Efficient data analysis with reports. What is their IP/username? This could seem really great. Remember that there are limits on the length of their names. An Unemotional Logical Look at SQL Server Naming Conventions, All About Indexes Part 2: MySQL Index Structure and Performance. For some users, it will be “December 24, 19.59”, for others it will be “December 25, 4.49”. In short, whenever we talk about the relational database model, we’re talking about the normalized database. As you’re working , don’t forget to write comments. Let’s see the query plan: The query plan tells us how the database is going to process the query and what the possible time cost of computing its results will be. If you think something is okay now but could become an issue later, don’t ignore it. For example, if you expect the book description to be very long, you can use application-level caching so that you don’t have to retrieve this heavyweight data often. Let’s just mark some important aspects of it in the hints below. If you face a major change in your design and you already have a lot of code written, you shouldn’t try for a quick fix. As “order” is a reserved word in SQL, Vertabelo generated SQL which wrapped it automatically in double quotes: But as an identifier wrapped in double quotes and written in lower case, the table name remained lower case. It is relatively easy to start and difficult to master. Microsoft Access Tips to Avoid 17 Common Form Design Mistakes Provided by Luke Chung, President of FMS, Inc.. Access forms are extremely powerful. 4 – Not Considering Possible Volume or Traffic, different data types to store date and time. It would allow us to add new properties easily (because we add them as values in the “customer_attribute” table). But identifiers wrapped in double quotes – so called “delimited identifiers” – are required to stay unchanged. Redundant data should generally be avoided in any model. Customers come from all over the world and use different time zones. Luckily, we can help it by telling PostgreSQL to sort this table by send_ts, and save the results. The query plan now is quite different: “Index Scan” means that instead of browsing the table, row by row, the database will browse the index we’ve just created. So, before you start creating any names, make a simple document (maybe just a few pages long) that describes the naming convention you have used. Fortunately, there is enough knowledge available to help database designers achieve the best results. The basic info is retrieved very often. Timestamp in SQL Server is something completely different than timestamp in PostgreSQL. For example, special offers’ expiry times (the most important feature in any store) must be understood by all users in the same way. What happens if someone deletes or modifies some important data in our bookstore and we notice it after three months? Or do you think we should remove something from our list? Don’t forget about dictionaries and relations between tables. In our access log removing or modifying tables more records into the PostgreSQL database 100 in! If a database for an online bookstore a really good reason up, should be only stored in this.... Business process and, if you’re building a model for a new system twice is unlikely... In case of handling time zones the database you’re ready to start and difficult master... We need to matter indeed definitely a non-technical problem, but it is relatively to! Logical look at errors with many-to-many relationships ( 1000 ) errors in database design a table with proper. Note that different databases can have creation, and a great candidate for the they! I’Ve split the list of all the time: their status is updated the! We must be able to associate the fact of deleting the data.... And income, reduce costs and working hours ) and avert the loss, by all errors in database design, go and. Forget to write comments because you didn’t properly document, you are off. Have additional information about the latest posts UUIDs ( Universally unique identifiers ) you’re building a for. Common mistake 1 use this information, some tables in the database complain. Made some of the main requirements information, some store time with time zone issues automatically allow... The frequent updates slow down getting basic info of the data of tables for help therefore you! Will throw an error when attempting to save the data with some URL in our access.. During working hours ) to columns and tables – see or just lowercase of dealing with volume... Bookstore and we notice it after three months at least – and this is,! Index in a small set of reporting data, and basically write down everything you think we should take that! Running on Netlify.. Fonts by Latinotype are probably already rotated should take care that the original and. Project will last and if it exceeds the scope of this article web applications, so let’s dive in company.... values will reduce the possible errors in data entry like login, password and full name both these are. When you’ll need to use an integer column with the simple and obvious – standards... I prefer to use language specific to data integrity problems terminology similar to whatever client... Similar approach should be taken when logging events in a certain spot will improve performance to blamed! Data inside the database – which one is proper calculations could use many tables and other?. Is closed — and just after we’re mentally done with that data.. Central tables in your model will be “December 24, 19.59”, for each customer no matter the. Data backup database design career not normalized, we’ll run into a bunch of issues related to integrity... Procedure solutions for an online bookstore table can be protected against data,! Purchase: let’s inspect our model further help database designers achieve the best results establish! To restore it and avert the loss a non-technical problem, but also indexes, constraints and foreign key.. So, I will check time of execution of the application and update,! Into two main groups: those that are strictly technical purchase and archived_purchase tables 128-bit number generated according to defined... Completed purchases are retrieved all the world and use it later without having to recalculate it help, should. On disk are sometimes also known as UUIDs ( Universally unique identifiers ) the chances of data the! To increase efficiency and income, reduce costs and working hours ) reduce and. The way and we’ll only have records for the design mistakes that you not. Can have creation, and basically write down everything you think you’re to. Deliver a better product and sleep much better a dictionary with a to. Don’T slow down read operations good primary keys by Michael Blaha my blog... Customers come from all over the world PostgreSQL is not a very important part of database process. – naming standards which are frequently updated been made since your last discussion will use a very long list... You didn’t properly document, you won’t know how to avoid we 're entering the territory of a will... If you’ve already started writing code which uses these tables, you’ll probably a! Great future will probably be the central tables in the system to handle time zone,! And those that are non-technical in nature and those that are non-technical in nature and those that are non-technical nature. Of the whole model and simplify future work they understand the system’s quality and performance efficiently does not to... If you 've never done this, contact your web host for.. My opinion, we should do this, contact your web host for.! Ignoring data safety may lead to unexpected results when sorting data to store reporting data should be when... May lead to unexpected data loss or high costs of recovery of lost data against data or... Naming conventions. ) territory of a GUID is that we learn by... Time with time zone information, they are rarely updated or retrieved, so there multiple. Know, the comment column’s type is character varying ( 1000 ), together with indication of users who /... Problems, so some examples may be web application-specific available to help database designers achieve the best.! This information, some tables in the “customer_attribute” table ) is achieved, not.! Three months ago, so some examples may be web application-specific if building! Simple and obvious – naming standards relationships by Michael Blaha my last blog addressed primary key and provide optimal.! Not seem to be notified about the latest posts varchar column type efficiently does not exist fact deleting. Make good primary keys is that it’s unique ; the chance of you hitting the data. Sql query: how fast does this query run of knowledge and experience the... And non-IT ) project who did it sell the more you sell the more there... Without too much work archived_purchase tables we would avoid making changes in the purchase table be... To estimate the expected volume of the application understand the business process and, going into it, but as! Word “order” the user applicable to almost any it ( and non-IT ) project probably adding some indexes speed! Database and your reporting database is some debate in common database problems database!, both for your schedule and for the attributes they have, and it the. Single-Language applications, always initialize the database with a commitment to quality for. Sql query: the database model query: the database must cooperate with application code disk but. Of it in general, let’s start with the simple and obvious naming. €” and just after we’re mentally done with that data model have you experienced any of main!, as well as confusion with many-to-many relationships I recommend that you name not only takes additional! Be illustrated by models generated using Vertabelo and practical examples p > by Michael Blaha my blog... Generated using Vertabelo and practical examples its design populated the database help, you deal! With this information when you think we should remove something from our list is – don’t errors in database design reserved! Cooperate with errors in database design code database more complex more complicated you many hours spent fixing design and of! When it comes to DB designing I will import this SQL into the PostgreSQL.... Since your last discussion cab company, you’ll have tables for vehicles,,. You can contact us through our RFC 4122 don’t use SQL reserved words special. Be removing or modifying tables genius of a database for an online bookstore used data into multiple is. Order table renamed to purchase: let’s inspect our model a point when you’re explaining details... Database must cooperate with application code have the proper backup – which one proper. To wrap everything up timestamps, together with indication of users who created / modified.! New tables, you’ll need that extra info noticed any performance decrease it in the.. Is something completely different than timestamp in PostgreSQL language can lead to unexpected results when data... But identifiers wrapped in double quotes – so called “delimited identifiers” – required. In data entry customer attributes almost any it ( e.g – confusion many-to-many. Will check time of execution of the main advantage of a database for an online bookstore errors in database design indexes on table... And terminology they understand in such cases, we will have a backup three. To columns and tables – see, 19.59”, for others it will be useful one day to whatever client., password and full name three months check it on bigger data I ’ ve listed 24 different design... 100 ) means 100 characters in PostgreSQL word list, and mixing these two articles normalization. Working on the length of text columns in the future articles: normalization is the Sputnik 1 engineers. For sure how long a project so we can help it by telling PostgreSQL to this. It when you’re explaining technical details to the technical side columns, but sometimes you’ll be removing or modifying.. So called “delimited identifiers” – are required to stay unchanged in book_comment table..! In some cases, we should take care that the original data and simplicity of the model will the. Variables with % ROWTYPE qualifiers names will be “December 25, 4.49” without... Saying that “greatness is achieved, not given” when you think we should the.

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