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Discovering Database Structure with VB .NET

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When you build a database yourself, you know what you've put in it. But what do you do if you have a legacy database thrust upon you? How do you figure out what tables are present? What fields are in the tables? How are the tables related? This article explains some useful techniques for learning about the structure of an MSDE or SQL Server database using Visual Basic .NET.
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If you're an experienced ADO programmer, you probably know that you can find out what fields a table contains by executing a SQL SELECT command and then examining the results. For example, the following statement selects all of the fields in the Customers table. After you execute it, you can look through the results to get the names of the fields.

SELECT * FROM Customers 

That's fine as far as it goes but an MSDE or SQL Server database can contain a lot of other important information. This technique doesn't tell you which fields are required, which have associated validation routines, which are related to fields in other tables as foreign keys, or which must have unique values.

Fortunately, SQL Server databases provide an overabundance of stored procedures that return information about the server and about the database. This article describes some of the more useful of those procedures.

Notes

Note that this only works for SQL Server and MSDE databases (MSDE is a restricted set of SQL Server. See my article, "Getting Started with MSDE and VB .NET," for information about MSDE databases). They won't work for Access, Oracle, Informix, or other databases. Oracle and other high-end databases may contain their own stored procedures for performing similar chores, however.

After you know what the stored procedures described here do, you'll need a way to execute them. You can easily write a Visual Basic .NET application that executes the procedures, examines the results, and takes whatever action is necessary. For example, a program might build an SqlConnection object, attach it to a database, and then use the sp_tables stored procedure to list the tables in the database. Processing the results is a bit outside the scope of this article, however.

My article, "Executing Ad Hoc Queries with VB .NET," shows how to build a program that can execute any SQL statement and display the returned values. You can use that program to run these stored procedures and examine the results. See that article for more details and to download the program.

The last section in this article also shows you how to make a program that uses the stored procedures to study the basic structure of a database. You can use that program as a starting point for your own.

Test Database

The examples shown in this article use a small quiz score database named TestScores. The database contains two tables, Students and TestScores, which were created using the following SQL script:

# Students.
CREATE TABLE Students (
  StudentId    INT      IDENTITY(1,1) PRIMARY KEY,
  FirstName    VARCHAR(20)  NOT NULL,
  LastName    VARCHAR(20)  NOT NULL,
  CONSTRAINT con_Students_Names UNIQUE (FirstName, LastName)
);

# Scores.
CREATE TABLE TestScores (
  StudentId    INT      REFERENCES Students (StudentId),
  TestNumber   INT      NOT NULL,
  Score      INT      NOT NULL CHECK ((Score >= 0) AND (Score <= 100)),
  CONSTRAINT pk_TestScores PRIMARY KEY (StudentId, TestNumber)
);

This script contains several interesting bits of database code including a UNIQUE constraint on the FirstName/LastName combination in the Students table, a CHECK constraint in the TestScores table, a two-field primary key in the TestScores table, and a foreign key in the TestScores table (the StudentId field references the Students table's StudentId field). Using SQL Server's stored procedures, a VB .NET application can learn about all of these things.

The following sections describe stored procedures that return information about the database at three different levels: server, database, and table.

Exploring the Server

In SQL Server, a server contains one or more databases. Usually, you need to work with a particular database, but you may need to find out what databases the server contains. You may also need to learn about the server itself. The following subsections describe some of the more useful server-level stored procedures.

sp_server_info

The sp_server_info stored procedure lists information about a server. The stored procedure returns a series of records with three fields: attribute_id, attribute_name, and attribute_value. The results include such values as the database management system's name (Microsoft SQL Server) and version, and whether the database supports save points and named transactions.

sp_helpserver

The sp_helpserver stored procedure returns a single record giving additional information about the server. The following table shows the values returned during one database session. Your program probably knows the name of the server to which it is connected, but the name and network_name fields may be useful if you don't have that information handy. For example, if you are building a small subsystem, it may be easier to fetch this information yourself than it would be to ask other developers to modify the part of the application that connects to the database.

Field Name

Value

name

BENDER\NetSDK

network_name

BENDER\NetSDK

status

rpc,rpc out,use remote collation

id

0

collation_name

NULL

connect_timeout

0

query_timeout

0


sp_who

The sp_who stored procedure returns information about the users and processes connected to the server. The following text shows some typical output. Most of the entries describe automatic database system processes. The program that generated this output is listed second-to-last. When the stored procedure ran, the program was connected to the OrderEntry database, and it was running a SELECT statement (as part of the stored procedure).

All of the processes in this output were logged in as sa (system administrator). If your database contains separate IDs for each user, the loginname field will be much more useful.

spid ecid status          loginame hostname blk   dbname     cmd       
==== ==== =============== ======== ======== ===== ========== ================
  1  0    background      sa        0       NULL    LAZY       WRITER   
  2  0    sleeping        sa        0       NULL    LOG        WRITER   
  3  0    background      sa        0       master  SIGNAL     HANDLER 
  4  0    background      sa        0       NULL    LOCK       MONITOR  
  5  0    background      sa        0       master  TASK       MANAGER  
  6  0    background      sa        0       master  TASK       MANAGER  
  7  0    sleeping        sa        0       NULL    CHECKPOINT SLEEP
  8  0    background      sa        0       master  TASK       MANAGER  
  9  0    background      sa        0       master  TASK       MANAGER  
 10  0    background      sa        0       master  TASK       MANAGER  
 11  0    background      sa        0       master  TASK       MANAGER  
 51  0    runnable        sa       BENDER   0       OrderEntry SELECT     
 52  0    sleeping        sa       BENDER   0       master     AWAITING COMMAND

sp_databases

The sp_databases stored procedure lists the databases available on a server. The following text shows the results of this statement on my database book's test server. Some of these, including master, are SQL Server system databases. For example, the master database contains the system stored procedures and other system information.

DATABASE_NAME   DATABASE_SIZE REMARKS
=============== ============= =======
Contacts                 3072 NULL  
Customers                3072 NULL  
master                  12480 NULL  
model                    1152 NULL  
msdb                    13312 NULL  
MultiUserOrders          3072 NULL  
Numbers                  3072 NULL  
OrderEntry               3072 NULL  
Orders                   3072 NULL  
tempdb                   8704 NULL  
TestAccounts             3072 NULL  
TestRoles                3072 NULL  
TestScores               3072 NULL  
TestSecurity             3072 NULL  
TestViews                3072 NULL  
Trans                    3072 NULL  

sp_helpdb

The sp_helpdb stored procedure returns additional information about the server's databases. The following text shows the results returned for my book's test server. The status field has been truncated because it is very long for some databases.

name            db_size       owner dbid created     status             compatibility_level
=============== ============= ===== ==== =========== ================== ===================
Contacts         3.00 MB       sa      7 Jan 3 2002   NULL                       80
Customers        3.00 MB       sa     13 Dec 12 2001  NULL                       80
master          12.19 MB       sa      1 Aug 6 2000   Status=ONLINE, ...         80
model            1.13 MB       sa      3 Aug 6 2000   Status=ONLINE, ...         80
msdb            13.00 MB       sa      4 Aug 6 2000   Status=ONLINE, ...         80
MultiUserOrders  3.00 MB       sa     16 Jan 12 2002  NULL                       80
Numbers          3.00 MB       sa      9 Dec 5 2001   NULL                       80
OrderEntry       3.00 MB       sa      5 Nov 5 2001   Status=ONLINE, ...         80
Orders           3.00 MB       sa     15 Jan 9 2002   NULL                       80
tempdb           8.50 MB       sa      2 Jan 16 2002  Status=ONLINE, ...         80
TestAccounts     3.00 MB       sa      8 Dec 3 2001   NULL                       80
TestRoles        3.00 MB       sa     10 Dec 7 2001   Status=ONLINE, ...         80
TestScores       3.00 MB       sa      6 Nov 7 2001   Status=ONLINE, ...         80
TestSecurity     3.00 MB       sa     11 Dec 7 2001   Status=ONLINE, ...         80
TestViews        3.00 MB       sa     12 Dec 7 2001   Status=ONLINE, ...         80
Trans            3.00 MB       sa     14 Dec 28 2001  Status=ONLINE, ...         80
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