Database Fundamentals #16: Removing Data With T-SQL

Database Fundamentals
Deleting data from a table using T-SQL works quite a lot like the UPDATE statement. How it Works In the same way you supply the statement, DELETE, and then the table name. You’re not going to specify columns in any way because deleting data is all about removing a row. If you just wanted to remove the values in a column, you would use the UPDATE statement. Because of this, the only other thing you need for a DELETE statement is the WHERE clause. Just like with the UPDATE statement, if you don’t supply a WHERE clause, then the DELETE statement will remove all data in the table. Be very careful about using this statement. Make sure you’ve always got a WHERE clause. This example would delete all the rows…
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Database Fundamentals #15: Modifying Data With T-SQL

Database Fundamentals, SQL Server 2005, SQL Server 2008, SQL Server 2012, SQL Server 2014, SQL Server 2016, SQL Server 2017
The preferred method for modifying your data within a database is T-SQL. While the last Fundamentals post showed how to use the GUI to get that done, it's not a very efficient mechanism. T-SQL is efficient. UPDATE The command for updating information in your tables is UPDATE. This command doesn’t work the same way as the INSERT statement. Instead of listing all the columns that are required, meaning columns that don’t allow for NULL values, you can pick and choose the individual columns that you want to update. The operation over-writes the information that was stored in the column with new information. In addition to defining the table and columns you want to update, you have to tell SQL Server which rows you’re interested in updating. This introduces the WHERE…
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Database Fundamentals #14: Modifying Data Through SSMS

Database Fundamentals
I've said it before, but I feel I should repeat myself. Using the SSMS GUI for data entry and data manipulation is not the preferred mechanism. T-SQL is the right way to manipulate the data in your database. For purposes of completion though, I will show the GUI methods in this blog series. Information doesn’t go into the database and stay there, unchanged, forever. Data is modified. This occurs because information changes, such as when a person marries and changes their name, or information was incorrectly entered, in which case you need to fix it, or just about anything else. You have to have a mechanism for modifying existing information. Modifying Data You start modifying data in the tables the same way you did the insert, by taking advantage of…
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Database Fundamentals #13: Data Entry Through T-SQL

Database Fundamentals
T-SQL provides lots of functions that help to make data entry through T-SQL much more powerful. Over time you won’t be typing everything into T-SQL directly as we’ll do here. You’ll be able to use stored procedures and parameters to automate the use of scripts. These will also be generated or used by applications. To  start using T-SQL, you need to open a query window. You can do this by right clicking on a database and selecting the “New Query” command from the context menu. This will open a new query window in the main window on your screen. This is basically just a big, open text box into which you can type commands. The INSERT Statement To add rows using T-SQL, the principal statement is the INSERT statement. The…
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Database Fundamentals #12: Adding Data with SSMS GUI

Database Fundamentals
In the previous Database Fundamentals, I argued that you should be learning T-SQL, yet the very next post I'm showing you how to use the GUI. What's up? Why the GUI? It's a very simple reason. I want to show you what it is so that I'm not hiding things. However, showing it to you will quickly expose the weaknesses inherent in using the SSMS GUI for direct data manipulation. It's a poor choice. However, we'll understand how it works at the end of this post. I'll also cover it in other posts, showing how to UPDATE and DELETE data using the GUI. They will further illustrate the weaknesses. You will however know how it works. Data Entry through the GUI If you are not already connected to the server,…
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Database Fundamentals #11: Why Learn T-SQL

Database Fundamentals
If you've been following along with the previous 10 Database Fundamentals blog posts, you have a SQL Server installed and a database with a table in it. You may have more if you've been practicing. Now would be the time to start adding data to the database, but first, I want to talk about the importance of T-SQL Why T-SQL? The way SQL Server accepts information is very different than most programs you’re used to using. Most programs focus on the graphical user interface as a mechanism for enabling data entry. While there is a GUI within SQL Server that you can use for data entry, and I will do a blog post on it, the primary means of manipulating data within SQL is the Transact Structured Query Language, or…
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Database Fundamentals #10: Modifying Tables

Database Fundamentals
Invariably, either while building a new database, or while maintaining old ones, you will find that the business needs change or that you’ve made a mistake. Either way, you will need to modify the tables that you’ve created. Change is inevitable and luckily SQL Server takes that into account, providing you with mechanisms to modify structures after you’ve created them. Important Warning One of the fundamental concepts of databases is that the data is stored. You can’t simply throw data away when you need to make a change to a table. There are two levels of changes you can make to a table. The first, is a change that won’t affect data in the table. These are simple changes and we’ll cover them in this blog post. The second level…
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Database Fundamentals #9: Schemas As Containers

Database Fundamentals
Schemas are a very useful tool for managing the objects in your database. From security through process, through placement, schemas provide you with another tool to control how your database behaves. Schemas The tables created so far in this blog series have all been attached to a schema, dbo. Depending on how you login to the server and the security settings for your user, this is usually the default schema. A schema is simply a container in which you place objects. Once placed there, a schema is a method for managing the objects it contains. Schemas give you a simple way to control placement of the objects on filegroups. Schemas are a very easy way to manage security. The use of schemas becomes extremely important as your database becomes more…
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Database Fundamentals #8: All About Data Types

Database Fundamentals
SQL Server provides all different kinds of data types in order to give you more flexibility and control for how you store your data. You define these data types as you define the columns in your tables. If you wanted to store information about the date and time that a purchase was made online you’re going to store the values in a column, or columns, that define dates and times in order to ensure accuracy in your data. Choosing a Data Type You could make the data type into one that stores just about anything you give it, such as one of the character types like char or varchar. Do this and you’re going to run into issues when you start running queries against that data. For example, your business…
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Database Fundamentals #7: Create a Table Using T-SQL

Database Fundamentals, TSQL
The syntax for creating a table logically follows many of the same steps that you did when using the GUI, but it will all be done with the statements. This script will exactly replicate everything that you did with the GUI: [crayon-5a6c1b9951b13292310977/] Breaking the script into separate lines, it’s easy to see how the TSQL commands perform the actions defined in the GUI (it also makes it easier to read). The CREATE TABLE statement in this context is self-explanatory.  After that you’re defining the schema and the table name. Within the parenthesis you define each of the columns. First is the name of the column followed by the data type and, for most columns, the ability of the column to store NULL values. The table will be stored on the…
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