A database is primarily a group of computer files that each has a name and a location. There are different ways to create a database. To visually create a new database in Microsoft SQL Server Management Studio, in the Object Explorer, you can right-click the Databases node and click New Database... This would open the New Database dialog box.
After creating an object whose name includes space, whenever you use that object, include its name between [ and ]. Examples are [Countries Statistics], [Global Survey], or [Date of Birth]. Even if you had created an object with a name that doesn't include space, when using that name, you can still include it in square brackets. Examples are [UnitedStations], [FullName], [DriversLicenseNumber], and [Country].
When originally creating a database, you may or may not know how many lists, files, or objects the project would have. Still, as a user of computer memory, the database must use a certain portion, at least in the beginning. The amount of space that a database is using is referred to as its size. If you use the New Database dialog box, after specifying the name of the database and clicking OK, the interpreter automatically specifies that the database would primarily use 2MB. This is enough for a starting database. Of course, you can either change this default later on or you can increase it when necessary. If you want to specify a size different from the default, if you are using the New Database to create your database, in the Database Files section and under the Initial Size column, change the size as you wish.
As you should be aware of already from your experience on using computers, every computer file must have a path. The path is where the file is located in one of the drives of the computer. This allows the operating system to know where the file is, so that when you or another application calls it, the operating system would not be confused. By default, when you create a new database, Microsoft SQL Server assumes that it would be located at Drive:\Program Files\Microsoft SQL Server\MSSQL10.MSSQLSERVER\MSSQL\DATA folder. If you use the New Database dialog box of the SQL Server Management Studio, if you specify the name of the database and click OK, the interpreter automatically creates a new file, and appends the .MDF extension to the file: this is the (main) primary data file of your database. If you do not want to use the default path, you can change it. If you are using the New Database dialog box, to change the path, under the Path header, select the current string: Replace it with an appropriate path of your choice.
When you install Microsoft SQL Server, it also installs 4 databases named master, model, msdb, and tempdb. These databases will be for internal use. This means that you should avoid directly using them, unless you know exactly what you are doing. One of the databases installed with Microsoft SQL Server is named master. This database holds all the information about the server on which your Microsoft SQL Server is installed. For example, you know that, to perform any operation on the server, you must login. The master database identifies any user who accesses the database, when, and how. Besides identifying who accesses the system, the master database also keeps track of everything you do on the server, including creating and managing databases. You should not play with the master database at the risk of corrupting the system. For example, if the master database is not functioning right, the system would not work.
Every statement in SQL can be terminated with a semi-colon. Although this is a requirement in some implementations of SQL, in Transact-SQL, you can omit the semi-colon. Otherwise, the above formula would be CREATE DATABASE DatabaseName; Here is an example: CREATE DATABASE NationalCensus; This formula is used if you don't want to provide any option. We saw previously that a database has one or more files and we saw where they are located by defauft. We also saw that you could specify the location of files if you want. To specify where the primary file of the database will be located, use the following formula: CREATE DATABASE DatabaseName ON PRIMARY ( NAME = LogicalName, FILENAME = Path ) The only three factors whose values need to be changed from this formula are the database name that we saw already, the logical name, and the path name. The logical name can be any one-word name but should be different from the database name. The path is the directory location of the file. This path ends with a name for the file with the extension .mdf. The path should be complete and included in single-quotes. Here is an example: CREATE DATABASE NationalCensus
ON PRIMARY
( NAME = DataRepository, FILENAME = 'C:\Exercises\NationalCensus.mdf')
GO
Besides the primary file, you may want to create and store a log file. To specify where the log file of the database would be located, you can use the following formula: CREATE DATABASE DatabaseName ON PRIMARY ( NAME = LogicalName, FILENAME = Path.mdf ) LOG ON ( NAME = LogicalName, FILENAME = Path.ldf ) Like the primary file, the log file must be named (with a logical name). The path ends with a file name whose extension is .ldf. Here is an example: CREATE DATABASE NationalCensus ON PRIMARY ( NAME = DataRepository, FILENAME = 'C:\Exercises\NationalCensus.mdf') LOG ON ( NAME = DataLog, FILENAME = 'C:\Exercises\NationalCensus.ldf') GO
To specify more options with code, Microsoft SQL Server ships with various sample codes you can use for different assignments. For example, you can use sample code to create a database. The sample codes that Microsoft SQL Server are accessible from the Template Explorer. To access the Template Explorer, on the main menu, you can click View -> Template Explorer. Before creating a database, open a new Query Editor. Then:
After any of these actions, Microsoft SQL Server would generate sample code for you. You would then edit the code and execute it to create the database. From the previous lessons and sections, we have reviewed some characters such as the comments -- and some words or expressions such as GO, CREATE DATABASE, and SELECT. We will study the other words or expressions in future lessons and sections.
While writing code in a Query Editor, you should always know what database you are working on, otherwise you may add code to the wrong database. Before visually making a database the current, a Query Editor must be opened. To visually select a database and make it the current, in the SQL Designer toolbar, click the arrow of the Available Databases combo box and select the desired database:
To programmatically specify the current database, in a Query Editor or using the SQLCMD utility (including PowerShell) at the Command Prompt, type the USE keyword followed by the name of the database. The formula to use is: USE DatabaseName; Here is an example: USE Exercise;
Some of the windows that display databases, like the SQL Server Management Studio, don't update their list immediately if an operation occurred outside their confinement. For example, if you create a database in a Query Editor, its name would not be updated in the Object Explorer. To view such external changes, you can refresh the window that holds the list. In SQL Server Management Studio, to update a list, you can right-click its category in the Object Explorer and click Refresh. For example, to refresh the list of databases, in the Object Explorer, you can right-click the Databases node and click Refresh.
If you have created a database but don't need it anymore, you can delete it. It is important to know, regardless of how you create a database, whether using SQL Server Management Studio, code in the Query Editor, or the Command Prompt, every database can be accessed by any of these tools and you can delete any of the databases using any of these tools. As done with creating a database, every tool provides its own means.
To delete a database in SQL Server Management Studio, in the Object Explorer, expand the Databases node, right-click the undesired database, and click Delete. A dialog box would prompt you to confirm your intention. If you still want to delete the database, you can click OK. If you change your mind, you can click Cancel.
To delete a database in a Query Editor, use the DROP DATABASE expression followed by the name of the database. The formula used is: DROP DATABASE DatabaseName; Before deleting a database in SQL, you must make sure the database is not being used or accessed by someone else or by another object.
A namespace is a group of "things" where each thing has a unique name. This can be illustrated as follows:
Notice that there are various types of objects within a namespace. For example, inside a company, each department has a unique name. Because two companies are independent, they can have departments that have the same name inside each company. To organize its own items, a namespace can have other namespaces inside. That is, a namespace can have its own sub-namespaces, just like a company can have divisions.
As mentioned already, a namespace can have objects inside. To further control and manage the objects inside of a namespace, you can put them in sub-groups called schemas. Therefore, a schema (pronounced skima) is a group of objects within a namespace. This also means that, within a namespace, you can have as many schemas as you want. This can be illustrated as follows:
Notice that, just like a namespace can contain objects (schemas), a schema can contain objects also (the objects we will create throughout our lessons). To manage the schemas in a namespace, you need a way to identify each schema. Based on this, each schema must have a name. In our illustration, one schema is named Schema1. Another schema is named Schema2. Yet another schema is named Schema_n. A schema is an object that contains other objects. Before using it, you must create it or you can use an existing schema. There are two types of schemas you can use, those built-in and those you create. When Microsoft SQL Server is installed, it also creates a few schemas. One of the schemas is named sys. Another is called dbo. The sys schema contains a list of some of the objects that exist in your database system. One of these objects is called databases (actually, it's a view). When you create a database, its name is entered in the databases list using the same name you gave it. To access the schemas of a database, in the Object Explorer, expand the Databases node, expand the database that will hold or own the schema, and expand the Security node. To visually create a schema, in the Object Explorer, expand the database:
This would open the Schema - New dialog box. In the Schema Name text box, enter a one-word name. Here is an example: After providing a name, you can click OK. The basic formula to create a schema is: CREATE SCHEMA schema_name_clause [ <schema_element> [ ...n ] ] Here is an example: 1> CREATE SCHEMA PrivateListing; 2> GO 1>
Inside of a schema, two objects cannot have the same name, but an object in one schema can have the same name as an object in another schema. Based on this, if you are accessing an object within its schema, you can simply use its name, since that name would be unique. On the other hand, because of the implied possibility of dealing with objects with similar names in your server, when accessing an object outside of its schema, you must qualify it. To do this, you would type the name of the schema that contains the object you want to use, followed by the period operator, followed by the name of the object you want to use. From our illustration, to access the Something1 object that belongs to Schema1, you would type: Schema1.Something1 When Microsoft SQL Server is installed, it creates a schema named dbo. This is probably the most common schema you will use. In fact, if you don't create a schema in a database, the dbo schema is the default and you can apply it to any object in your database.
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