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Nội dung Text: MASTERING SQL SERVER 2000- P3

  1. 70 CHAPTER 3 • OVERVIEW OF SQL SERVER DB-Library Options Tab One of the features that makes SQL Server such a powerful tool is the variety of meth- ods that you can use to retrieve data from it. You can execute Transact-SQL code using tools such as Query Analyzer or the OSQL command line tool, or you can write your own custom programs. DB-library is one of the tools available for writing custom pro- grams using a language like C++ or Visual Basic. DB-library is an application program- ming interface (API), which is a collection of functions and commands that developers can access through their own code. Using APIs, developers do not need to rewrite code that Microsoft has already writ- ten. This makes the developer’s job much easier. As Microsoft makes changes and updates to the code in SQL Server, the DB-library API gets upgraded, which means that you may occasionally need to get a new copy from the Microsoft Web site. To ascertain which version of the API you have loaded on your system, check the DB- library information box at the top of the DB-Library Options tab. This tells you the version, size, and date of the DB-library file you are using. Not only can you view the version of the DB-library installed on your machine using the DB-Library Options tab, you can also set two options that can change the way your DB-library works: Automatic ANSI to OEM Conversion: This setting will allow the DB- library to convert data from the client (OEM) into data that SQL Server will understand (ANSI) and vice versa. Use International Settings: This setting will allow the DB-library to get date, time, and currency formats from the server, instead of you having to hard code the formats into all your applications.
  2. PROGRAMS INSTALLED WITH SQL SERVER 71 Network Libraries Tab PA R T The sole function of the Network Libraries tab is to display the version number and I date of the network library files that you have installed on your local system. If your files are out of date, you can upgrade them by installing the latest service pack (dis- cussed in Chapter 1). The best way to tell whether these files are out of date is to Introducing SQL check your version numbers on the Network Libraries tab and compare them with the version numbers that Microsoft posts in the service pack readme file. A readme file will contain information on all of the fixes and new file versions that come with the service pack. Server Server Network Utility The Server Network Utility, located in the Microsoft SQL Server 2000 group in the Pro- grams group on the Start menu, works much the same as the Client Network Utility in that it is used to configure the net-libraries on which the server listens. The biggest dif- ference that you may notice is the addition of the WinSock Proxy information. With this proxy information, you can configure SQL Server to listen for client calls over the Internet through a Microsoft Proxy Server. All you need to do is check the Enable WinSock Proxy checkbox and supply the IP address or computer name of the proxy server as well as the port number for the proxy server to listen on. The Network Libraries tab here performs the same function as the Network Libraries tab in the Client Network Tool.
  3. 72 CHAPTER 3 • OVERVIEW OF SQL SERVER Service Manager Having only one function, the Service Manager is a simple tool compared to the rest. The Service Manager exists to start, stop, pause, and monitor the status of your SQL Server services. The easiest way to get to this tool is by double-clicking the small server icon in your Taskbar tray—or you can get to it from the SQL Server 2000 group in Programs on the Start menu. Once opened, this tool can be used to start, stop, or pause any of the four SQL Server services. Distributed Transaction Coordinator: Primarily used to control trans- actions that are distributed between multiple servers, this service is covered in Chapter 8. MSSQLServer: This service is the heart of SQL Server, because it performs such functions as executing queries, managing access to data, and allocating system resources (such as RAM and CPU). SQLServerAgent: This service will be discussed in detail in Chapter 14, but it controls automation. This service will execute tasks (such as backing up a database) and send e-mail in the event of a problem. Microsoft Search: This service creates and maintains full-text search indexes. These indexes allow users to perform faster searches on fields of the text datatype. We’ll discuss full-text search in Chapter 6.
  4. PROGRAMS INSTALLED WITH SQL SERVER 73 PA R T I Introducing SQL Server N OTE When you look at the icon in the system tray, you will notice a green arrow, which means your service is running. If the arrow is red, your service is stopped. Yellow means paused. TI P You can also perform Service Manager operations by right-clicking the Service Man- ager icon in the system tray. Profiler Once you have successfully designed and deployed your databases, and your users are accessing them on a regular basis for inserting, updating, and deleting data, you need to monitor the server to make sure it is running the way it is supposed to. You need to know such things as how fast the server is running, what sort of data the users are accessing, and whether anyone is trying to hack into your server. In the SQL Server 2000 group in the Programs group on the Start menu, you will find Profiler, a powerful monitoring tool that can show you all of this information and a great deal more. Using Profiler involves setting up event-monitoring protocols, called traces. An event is anything that happens to a running system, such as a failed or successful login, a query being properly routed and the results retrieved, or a report being run. You can design each trace to look at specific aspects of the system, which you’ll get a
  5. 74 CHAPTER 3 • OVERVIEW OF SQL SERVER chance to do in Chapter 26. By monitoring events, you can tell how the system is being used and whether anything needs tweaking for greater efficiency. NOTE For more information on using SQL Profiler, see Chapter 24. Query Analyzer In Start ➣ Programs ➣ SQL Server 2000, you will find Query Analyzer, a graphic tool that allows you to execute collections of Transact-SQL statements, called queries. Most of the queries executed in Query Analyzer will be SELECT queries, designed to display data stored in your database tables. Other examples of queries that you can execute here might be DELETE queries, designed to remove data from your database, or INSERT queries, which add data. Some of the queries you execute with this tool will not modify your data; rather, they will modify the structure that holds your data. These types of queries are referred to as data definition statements, and they are used to accomplish such tasks as creating tables, indexes, views, users, etc. Any Transact-SQL code that you need to run can be executed using this tool. However, that is only half of what it does.
  6. PROGRAMS INSTALLED WITH SQL SERVER 75 PA R T N OTE Throughout this book, you will see the term query, which is a term used to I describe a request for data from SQL Server. This request is made using Transact-SQL state- ments, usually a SELECT statement (which is designed specifically for the purpose of retrieving data). Introducing SQL Query Analyzer not only executes Transact-SQL queries, it analyzes them as well (thus the name). The analysis will tell you such things as how much CPU time the query took to run, how much time it spent reading from the hard disk, etc. Once you Server know how much time and resources your queries take to run, you can tune them accordingly. If your queries run too slowly, you can rewrite them to make them run faster (that discussion is in Chapter 6). If you take a look at Figure 3.1, you will see a picture of Query Analyzer displaying the results of a query for all of the records in the Authors table of the pubs database. The top half of the screen contains the actual SELECT query, and the bottom half of the screen contains the results of that query, called the result set. FIGURE 3.1 Query Analyzer is used to execute Transact-SQL code and display the results.
  7. 76 CHAPTER 3 • OVERVIEW OF SQL SERVER NOTE When you first open Query Analyzer, you will see the Object Browser. We have closed it for many of the examples in this book for the sake of simplicity. You’ll learn how to use Query Analyzer in more detail in Chapter 5. OSQL OSQL is a command line tool that executes Transact-SQL code and displays the results, just like Query Analyzer. Aside from the fact that Query Analyzer is graphical and OSQL is a command line tool, there is only one small difference between the two: OSQL does not have the ability to analyze queries and display statistics on speed of execution. Other than that, the two tools perform much the same function, executing Transact-SQL code. This begs the question, “Why use OSQL if you have Query Ana- lyzer?” The answer is scheduling. Suppose that you have a sales manager who needs to see daily figures on sales. Because you cannot schedule Query Analyzer to run a command automatically, you would need to instruct the manager how to execute a query in Query Analyzer so that they could manually extract the data every night. Not many managers out there have this kind of time on their hands, though. Another method you could consider is creating a job to automate the task. A job is a series of steps that can be executed automatically by SQL Server. One of those steps could be the query that extracts the data your manager needs, but there is no way to get that data from a job to the manager. OSQL can be used to run the query and save the data to a text file. The command can also be scheduled (using such tools as the Windows NT AT command or a SQL Server job) to run automati- cally. The manager can then read the text file whenever they want. NOTE OSQL runs in one of two modes: interactive or batch. Interactive mode func- tions much like Query Analyzer in that it allows you to enter commands at a prompt, and when you finish, you type EXIT. Batch mode sends a single command to the server and returns a result set. Batch mode is used for automation. Several arguments can be used to control the behavior of the OSQL program. All of them are case-sensitive, which means that an uppercase E means something entirely different than a lowercase e. The arguments that you can use are listed here: -Uusername: To send queries to a SQL Server, you must gain access by log- ging in. There are two ways to log in. One way is by using a trusted connection,
  8. PROGRAMS INSTALLED WITH SQL SERVER 77 which means that SQL Server trusts Windows NT to verify your username and PA R T password. The second way is by establishing a nontrusted connection, which I means that SQL Server must verify your username and password. The -Uuser- name parameter tells SQL Server which user to log you in as using a nontrusted connection. Therefore, if you want to log in as a user named Bob, the -U para- meter would look as follows: -Ubob. Introducing SQL -Ppassword: This specifies the case-sensitive password to be used in con- junction with the -U parameter. If you are logging in as Bob and your password is doughnut, the -P parameter would look as follows: -Pdoughnut. Server -E: This specifies a trusted connection, where SQL Server trusts Windows NT to verify your username and password. This requires no username or password to be entered because OSQL will detect the username and password you used to log on to your computer, and use that same information to log you in to SQL Server. -Sserver_name: This specifies the name of the server that you want to con- nect to in order to perform queries. The -Slondon parameter, for example, would connect you to a server named london. -L: If you cannot remember the name of the server you want to connect to in order to query, the -L parameter detects all of the SQL Servers on the network and displays a list for you. -e: This parameter will repeat (or echo) the commands that you type. If you enter a query, for example, it will be repeated on the first line of the result set. -p: This parameter will print performance statistics about the query executed. It displays execution time, extracted records per second, and network packet size. -n: In interactive mode, you normally see line numbers before each line of text that you type as well as a > symbol. The -n parameter removes the line numbers and the > symbol. -ddb_name: This sets the database with which you will be working. If you want to query one of the tables in the pubs database, for example, this parame- ter would be -dpubs. -Q“query”: This will execute the query encased in quotation marks and immediately exit the OSQL program. Note that queries must be encased in double quotes. -q“query”: This also executes the query in quotes, but does not exit OSQL after execution. Once the query is finished, you remain in interactive mode. -ccmd_end: Ordinarily, when working in interactive mode, you must enter the word GO on a line by itself to tell OSQL that you have finished entering
  9. 78 CHAPTER 3 • OVERVIEW OF SQL SERVER code and it should be executed now. This is called a command terminator. Using this parameter, you can set a different command terminator. -hheaders: By default, you will see the names of the columns in the result set printed only once, at the top of the result set. If this is not enough, you can use the -h command to print the header more often. The -h5 parameter reprints the names of the columns (the headers) every five lines. -wcolumn_width: The default number of characters that are displayed on a single line of output is 80. The -w parameter changes that to be more or fewer characters. For example, -w70 would display only 70 characters on a line of output. -scol_separator: The default method of separating columns on the screen is to use a blank space. Because this may be difficult for some people to read, you can change the separator using the -s parameter. For instance, -s> would sepa- rate your columns from one another using the > symbol. -ttimeout: If a command fails while it is running (for example, the SQL Server goes down), the command will run indefinitely by default. To change that behavior, you can specify a timeout parameter. For example, -t5 would instruct OSQL to time out after waiting 5 seconds for a response. -merror_level: SQL Server recognizes several levels of error severity from 1 to 25; 1 is the lowest (reserved by SQL Server), 10 is informational (something happened, but it’s not too bad), and 25 is the highest (your server is having a stroke). The -m parameter tells OSQL which levels to display; for instance, -m10 displays all level 10 errors and higher, but nothing lower. -I: In interactive mode, you ordinarily place strings of text inside single quotes (‘’). With this option set, you can encase text strings in double quotes instead (“”). -r {0 | 1}: Because not all error messages are printed to the screen, you can use this parameter to redirect them to the screen. The parameter -r0 will display error messages of 17 or higher, and -r1 will display all messages on the screen. -Hwksta_name: With this parameter, you can specify the name of the com- puter from which you are connecting. The default for this is the computer name. However, if you are on a Windows NT machine that has both a com- puter name (used by other Microsoft machines) and a hostname (used by Unix machines and other TCP/IP hosts), you can instruct OSQL to connect as your hostname rather than your machine name.
  10. PROGRAMS INSTALLED WITH SQL SERVER 79 -R: Various settings control the process of converting currency, date, and PA R T time values into character data to be displayed on the screen. The -R setting I instructs OSQL to use the client settings rather than the server settings to per- form this conversion. -iinput_file: SQL Server can accept a text file as an input parameter by using the -i parameter. This means that you can enter all of your settings and your Introducing SQL query in a text file (using something like Notepad), and then, instead of enter- ing all of the information on the command line every time, you can specify an input file. Server -ooutput_file: This will copy the result set to a text file, as opposed to the screen (which is the default). The -oc:\output.txt parameter, for instance, copies the result set from your query to a file named output.txt. -u: This is used in conjunction with the -o parameter to specify that the out- put file be stored as Unicode data rather than ASCII (the standard character set that displays 256 characters). This is useful for companies that store data in multiple languages. -apacket_size: This specifies the amount of data (in kilobytes) that SQL Server will send to or receive from OSQL at a time, called a packet of data. The default size is 512KB, which works fine for most transfers, but if you are performing a bulk insert of data from a large text file into a table, you may want to increase this to 8192 (Microsoft recommends this based on their testing). -b: This parameter instructs OSQL to exit to DOS and return a DOS error level of 1 when a problem arises. DOS error levels can be used in batch files for troubleshooting. -O: This forces OSQL to behave more like its precursor, ISQL. This parameter sets the default DOS ERRORLEVEL value to –1 and specifically turns off the fol- lowing features: EOF batch processing Automatic console width scaling Wide messages -ltimeout: This specifies the amount of time that OSQL will wait for a login to be verified. If this parameter is not specified, OSQL will wait indefinitely. -?: This parameter will display a list of all the available switches to be used with OSQL.
  11. 80 CHAPTER 3 • OVERVIEW OF SQL SERVER Fortunately, you do not need to specify every parameter listed here to make OSQL work. Let’s look at using OSQL to run a query and save the results to a text file: 1. To get to the command prompt, click your Start button, select Programs, and click the Command Prompt icon. 2. To execute a query with OSQL, type the following command at the command prompt: OSQL –Sserver_name –dpubs –Q”select * from authors” –Usa –Ppassword –ooutput.txt 3. Open output.txt with a text editor such as Edit. The result set should display all of the records in the Authors table in the pubs database. Another command line tool that may come in handy is BCP, the Bulk Copy Program. Bulk Copy Program (BCP) Once you have created databases in SQL Server, you will need to fill them with data. A popular way to do this is by importing text files into your tables. If you opt for this route, you can use the Bulk Copy Program (BCP), which is a command line tool designed solely for the purpose of importing and exporting text files to and from tables at the rate of about 2000 rows per second (for you Trekkies, that’s about WARP 9.9). This program is still here to provide backward compatibility and is being replaced by faster methods of import, such as the Bulk Import Transact-SQL command. This com- mand will be discussed in more detail in Chapter 14. Enterprise Manager Many of the administrative tasks you perform with SQL Server will be accomplished using Enterprise Manager. Using this tool, you can create databases and all of their associated objects (tables, views, etc.). You can perform maintenance tasks such as database backups and restorations. Server and database security can be maintained from this tool, error logs can be viewed, and much more. When you first open Enter- prise Manager, you should see something that looks like Figure 3.2.
  12. PROGRAMS INSTALLED WITH SQL SERVER 81 FIGURE 3.2 PA R T Enterprise Manager is I used for many admin- istrative tasks. Introducing SQL Server The tool that you are seeing in Figure 3.2 is actually the Microsoft Management Console with an Enterprise Manager snap-in. The Microsoft Management Console (MMC) is designed to conglomerate your applications so that you can manage all of them from a single interface. The application-specific tools that MMC hosts are called snap-ins. To manage a new application with MMC, all you need to do is insert a snap-in. The snap-in is the most basic part of the MMC, allowing you to access your programs. What you are seeing when you look at the Enterprise Manager is the Enterprise Manager snap-in for the Microsoft Management Console. There are two panes in the Enterprise Manager, the contents pane on the right and the tree pane on the left. By clicking the + icons next to the container objects in the tree pane on the left, you can drill down to greater levels of detail. By examining the contents pane, you will be able to see the objects contained in the container objects. For example, if you click the + icon next to Microsoft SQL Servers, and then on SQL Server Group, and finally on your server, you will see the same thing as in Figure 3.2. By expanding Databases, expanding pubs, and then clicking the Tables icon, you will see the contents pane fill with the names of all available tables in the pubs database, as shown in Figure 3.3.
  13. 82 CHAPTER 3 • OVERVIEW OF SQL SERVER FIGURE 3.3 Displaying the pubs database tables in Enterprise Manager As we journey through the rest of this book, you will be exposed to Enterprise Manager on an ongoing basis and will gain a great deal of experience with it. Now that you have a general overview of the tools available to you, you’ll need to under- stand what you will be creating with those tools. Let’s take a look at the various parts of a database. NOTE For more information on the capabilities of SQL Server Enterprise Manager, see Chapter 9. Parts of a Database As Microsoft describes it, a database is an object that contains tables and other objects that are combined to facilitate data retrieval. In essence that is true, but you can think of a database as being more like a toolbox. If you own any amount of tools, you prob- ably don’t just have them scattered about your property. If you did, you would have no way of finding them when you needed them. Rather, you put them all in a tool- box. Your wrenches go in the wrench drawer, screwdrivers in the screwdriver drawer,
  14. PARTS OF A DATABASE 83 and so on. When your tools are organized that way, you know exactly where to look PA R T when you want a particular tool. I A database is like a toolbox in that it is useless by itself, but when you fill it with other objects (tables, views, etc.), it serves a purpose by keeping those objects orga- nized. Now when you want data, you know exactly where to go to get it. If, for instance, you want accounting data, you go to the Accounting database and dig Introducing SQL through the accounting tables to find your data. Because a database is primarily a conglomeration of objects, you need to under- stand those objects before you can successfully use a database. Let’s look at some of Server those now, starting with tables. Tables Tables are the objects in the database that actually store the data. Because all other objects in the database depend on their existence, tables can be considered the build- ing blocks of the database. The data stored in tables is organized further into fields and rows. A field can be thought of as a vertical element in the table and contains information of the same type, such as last name or zip code. Fields are organized into columns. A record can be thought of as a horizontal element and contains informa- tion that spans all of the fields in the table within a single row. One record in an employee database, for example, might contain the last name, first name, address, Social Security number, and hire date of a single employee. A spreadsheet, such as that shown in Figure 3.4, may help you to visualize fields and records a little better. FIGURE 3.4 Last Name Tables are organized Field into fields and records. Varchar datatype Lastname Firstname Address Hiredate Varchar(25) Varchar(15) Char(30) Datetime Jorden Joe 12 Main St. 1/1/99 Joe Jorden Record Gunderloy Mike 156 South 3rd 2/7/95 Spiller Melanie 9087 Marina Parkway 8/9/87
  15. 84 CHAPTER 3 • OVERVIEW OF SQL SERVER Each of the fields in a table can contain only one type of data, such as character or numeric data. This aspect of the field is referred to as the column’s datatype. In the example presented in Figure 3.4, you’ll notice that the address column has a datatype of char (30), which means that this column holds 30 characters. If any numbers are stored here, you will not be able to perform any mathematical functions on them (such as adding or subtracting) without first converting the values stored in the field to numeric data. Once you have tables created in your database (which we’ll discuss in more detail in Chapter 11), you can start creating other objects that depend on them, such as views or stored procedures. Views Much like tables, views are comprised of fields and records. Unlike tables, views do not contain any data. Views are always based on tables and are used to provide a different perspective of the data stored in those tables. For example, suppose that you have a human resources database that contains employee names, addresses, phone numbers, Social Security numbers, and pay rates. The names, addresses, and phone numbers are usually public information, but the Social Security numbers and pay rates are not meant for the general populace. One way to secure this data so that only authorized people can see it is by creating a view that does not contain the latter two columns and setting permissions on the table and view. This way, only people with the proper authority can read from the table itself, and everyone else can read from the view. You can use the view method to store the data only once (in the table), but still have two ways of looking at it. Figure 3.5 ought to help you visualize this a little better. FIGURE 3.5 Lastname Firstname Address Views can display select fields from a Jorden Joe 12 Main St. single table. Gunderloy Mike 156 South 3rd Spiller Melanie 9087 Marina Parkway Lastname Firstname Address SSN Payrate Jorden Joe 12 Main St. 555-66-7777 1.00 Gunderloy Mike 156 South 3rd 666-77-8888 1.00 Spiller Melanie 9087 Marina Parkway 888-99-0000 1.00
  16. PARTS OF A DATABASE 85 Another valuable service provided by views is the combining of data from two or PA R T more separate tables into one easy-to-read format. For instance, suppose that you I have two tables, one that contains customer information such as name, address, and so on, and a separate table that contains information about what those customers have ordered from you. If you want to see your customers’ names, addresses, and details about what they have ordered, you can create a view that combines the two Introducing SQL tables and presents the data all at once, rather than executing two separate queries to get the data. Figure 3.6 should help you visualize the concept. Server FIGURE 3.6 This view pulls data View based on CustID Name QTYordered from multiple tables multiple tables 1 Bob Smith 27 and presents it all in one place 2 John Doe 32 3 Sam Jones 56 CustID Name Address CustID Product QTYordered 1 Bob Smith 12 First 1 Screws 27 2 John Doe 17 Main 2 Bolts 32 3 Sam Jones 145 3rd 3 Wingnuts 56 TI P Why not just store the data in the format that you’d like to view it in later? Because the organization that makes the most sense to human beings may not make the most sense for quick and error-free data storage and retrieval. The name for this notion is nor- malization, and you can read much more about it in Chapter 4. Stored Procedures You already know that data is stored in tables and that you need to execute queries to read the data in the tables. But where should those queries be stored? One place to store them is in a database on the server. Such stored queries are called stored proce- dures. You could also store the queries in the code on the client machines, or you could allow the users to generate these queries themselves using Query Analyzer;
  17. 86 CHAPTER 3 • OVERVIEW OF SQL SERVER these are called ad hoc queries. Stored procedures are generally preferred because of the problems that are inherent with the spontaneity of ad hoc queries. The first problem is that all of your users will be performing queries to get the data out of the tables, all of those queries will be traversing the network, and all will cause network traffic. If all of those queries contain several lines of text, you can imagine the havoc that would be wreaked on your bandwidth. Another problem caused by ad hoc queries is that they can also slow SQL Server down. When an ad hoc query is sent to SQL Server the first time, it cannot be exe- cuted right away; it must first be compiled. To compile a query, SQL Server must read the query and figure out the fastest way to execute it by comparing the query to the available indexes. The process of compiling takes system resources (such as CPU time and RAM) and slows the system down. NOTE To accelerate query processing speed, SQL Server uses indexes. Indexes speed up data access by keeping a list of all the values in one or more fields of a table and point- ers to where the records that contain those values are located. Indexes are discussed in detail in Chapter 12. An interesting fact about users is that most of them want to see the same data as everyone else, which means that all of your users are sending the exact same queries to the SQL Server over the network. Instead of having each of your users send the same query a bunch of separate times over the network, you can store the query on the server (called a stored procedure) and have the users send a simple command to have SQL Server run the stored procedure. This way, instead of sending several lines of text over the network and wasting bandwidth, your users send a simple, one-line command: execute stored_procedure. These stored procedures are also precompiled, which means that you are saving system resources as well. NOTE For a detailed discussion of stored procedures, please see Chapter 14. Diagrams When you looked at the tables container in the pubs database earlier in this chapter, chances are that you did not find it very easy to look at. That is a natural reaction for most people: People don’t like staring at long lists trying to find what they need. That is why there are database diagrams.
  18. PARTS OF A DATABASE 87 A database diagram is a graphical representation of a database that shows all of the PA R T objects in the database and how they relate to one another. Using a diagram, you can I change table structure (for example, adding fields), relate them to other tables, and even create new indexes for them (all of which are discussed later). Without these dia- grams, you would need to find each object individually in its own container and try to work with each separately, a mind-numbing task indeed. The following graphic Introducing SQL shows what a diagram of the pubs database might look like. Server NOTE You’ll learn more about creating and using database diagrams in Chapter 11. Database User Accounts As mentioned earlier, most companies store data that is not meant for the general populace of the company. Not everyone is privy to pay rates and Social Security num- bers, for instance. So how do you keep prying eyes out of places they don’t belong? With database user accounts.
  19. 88 CHAPTER 3 • OVERVIEW OF SQL SERVER To access SQL Server, users must have what is called a login account. There are two types of login accounts that you can give to your users: standard and integrated. An integrated account is also referred to as a trusted connection, because with this type of login, SQL Server trusts Windows NT to verify the username and password. This type of login can be used only for Microsoft clients, such as Windows 98 or Windows NT. Standard accounts do not trust Windows NT to verify account information and there- fore are useful for clients that do not have a Windows NT account, such as Macintosh or Unix clients. Either type of login account will let your users access SQL Server as a whole, but not the individual databases. To give users access to individual databases, you must create a database user account for them in each database where they require access. For example, suppose that you have a user named Bob who requires access to the Accounting database, but is not allowed to access the Sales database for any reason. To grant Bob access to the Account- ing database, you would create a database user account in the Accounting database. This database user account will allow Bob access to the Accounting database. Because you do not want Bob to access the Sales database, if you don’t create a database user account for him in the Sales database, he won’t be able to get in without it. This is just an overview, of course. Security will be discussed at length in Chapter 18. Database Roles Many large companies have thousands of users, assigned organizationally into vari- ous departments. Each of the people in the various departments requires access to the same segments of information. For instance, accounting personnel all need access to the accounting data, sales personnel need access to the sales data, and so on. There are two ways to get users the access they need. The first way is to create user accounts for each and every one of the users (which you have to do anyway) and then individ- ually grant permissions to each user. The second and much easier way is to create the user accounts and assign the accounts to roles in the database. A role is a predefined set of permissions to which you can add users. Once the user is a member of a role, they inherit the permissions of that role, and you need not individually assign them permissions. For example, if everyone in your accounting department needs to be able to read data from the accounting tables, you could assign the individual users’ accounts to a role that already has the appropriate permission— and voila, they are able to read the data.
  20. PARTS OF A DATABASE 89 User-Defined Datatypes PA R T I As discussed earlier, each of the fields in a table can contain only data of a certain type referred to as the datatype. SQL Server has several built-in datatypes, including: bit: Integer data with either a 1 or a 0 value. 31 31 int: Integer (whole number) data from –2 (–2,147,483,648) through 2 – 1 Introducing SQL (2,147,483,647). 15 15 smallint: Integer data from –2 (–32,768) through 2 – 1 (32,767). tinyint: Integer data from 0 through 255. Server 38 decimal: Fixed precision and scale numeric data from –10 – 1 through 38 10 – 1. numeric: A synonym for decimal. 63 money: Monetary data values from –2 (–922,337,203,685,477.5808) 63 through 2 – 1 (922,337,203,685,477.5807), with accuracy to a 10,000th of a monetary unit. This monetary unit can be set by adding any one of the follow- ing units of measure: • Dollars • Pounds • Yen • Bengali Rupee • Thai Baht • Euro-Currency • Cruzeiro • Franc • Lira • Nira • Peseta • Won • New Sheqel • Dong smallmoney: Monetary data values from –214,748.3648 through 214,748.3647, with accuracy to a 10,000th of a monetary unit. This uses the same monetary units as money. float: Floating precision number data from –1.79E + 308 through 1.79E + 308.
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