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Learning About Tables

After you know what databases are available on the server, you can look for information about the tables in a database. The following sections describe stored procedures that describe tables.

Note that the program must be using a database before it can execute these procedures. For example, to use the sp_tables procedure to see what tables are in the TestScores database, the program must be connected to the TestScores database. A simple SQL script to use the TestScores database and then execute the sp_tables procedure would look like this:

USE TestScores;
sp_tables;

sp_tables

The sp_tables stored procedure lists the tables in a database. For example, the sp_tables statement produces the following output for the TestScores database.

TABLE_QUALIFIER TABLE_OWNER TABLE_NAME          TABLE_TYPE   REMARKS
=============== =========== =================== ============ =======
TestScores          dbo     syscolumns          SYSTEM TABLE NULL  
TestScores          dbo     syscomments         SYSTEM TABLE NULL  
TestScores          dbo     sysdepends          SYSTEM TABLE NULL  
TestScores          dbo     sysfilegroups       SYSTEM TABLE NULL  
TestScores          dbo     sysfiles            SYSTEM TABLE NULL  
TestScores          dbo     sysfiles1           SYSTEM TABLE NULL  
TestScores          dbo     sysforeignkeys      SYSTEM TABLE NULL  
TestScores          dbo     sysfulltextcatalogs SYSTEM TABLE NULL  
TestScores          dbo     sysfulltextnotify   SYSTEM TABLE NULL  
TestScores          dbo     sysindexes          SYSTEM TABLE NULL  
TestScores          dbo     sysindexkeys        SYSTEM TABLE NULL  
TestScores          dbo     sysmembers          SYSTEM TABLE NULL  
TestScores          dbo     sysobjects          SYSTEM TABLE NULL  
TestScores          dbo     syspermissions      SYSTEM TABLE NULL  
TestScores          dbo     sysproperties       SYSTEM TABLE NULL  
TestScores          dbo     sysprotects         SYSTEM TABLE NULL  
TestScores          dbo     sysreferences       SYSTEM TABLE NULL  
TestScores          dbo     systypes            SYSTEM TABLE NULL  
TestScores          dbo     sysusers            SYSTEM TABLE NULL  
TestScores          dbo     Students                   TABLE NULL  
TestScores          dbo     TestScores                 TABLE NULL  
TestScores          dbo     sysconstraints      VIEW         NULL  
TestScores          dbo     syssegments         VIEW         NULL  

Of the tables shown, I created only the Students and TestScores tables. All of the others are automatically created by the database. Those tables contain information about the database itself. You can query these tables directly to learn more about the database, although it is often easier to find a stored procedure to make the query for you.

sp_pkeys

The sp_pkeys stored procedure gives information about a table's primary key. For example, the statement sp_keys TestScores returns the following results.

TABLE_QUALIFIER TABLE_OWNER TABLE_NAME COLUMN_NAME KEY_SEQ PK_NAME   
=============== =========== ========== =========== ======= =============
TestScores      dbo         TestScores StudentId     1     pk_TestScores
TestScores      dbo         TestScores TestNumber    2     pk_TestScores

This output indicates that the TestScores table's primary key consists of the StudentId and TestNumber fields. The KEY_SEQ field gives you the ordering of the fields within the key.

sp_fkeys

The sp_fkeys stored procedure gives information about a table's foreign keys. This procedure returns a lot of fields so they are not all shown here. Probably the most important fields are PKTABLE_NAME, PKCOLUMN_NAME, FKTABLE_NAME, and FKCOLUMN_NAME. These fields give the names of the primary and foreign tables and their related columns. The KEY_SEQ field gives the ordering of the fields if they are in a sequence that must match. For example, if the FirstName and LastName fields in one table must match the FName and LName fields in another table, KEY_SEQ tells you how to order the fields.

The following text shows these columns in the results for the statement sp_fkeys Students executed on the test database.

PKTABLE_NAME PKCOLUMN_NAME FKTABLE_NAME FKCOLUMN_NAME KEY_SEQ
============ ============= ============ ============= =======
Students     StudentId     TestScores   StudentId      1

sp_helpconstraint

The sp_helpconstraint stored procedure returns information about a table's CHECK and foreign key constraints. The following output shows the result of the SQL statement sp_helpconstraints TestScores with some of the less-interesting fields removed. The results identify the TestScores table's CHECK constraint, the fact that its StudentId field is related to the Students table's StudentId field, and the primary key that includes the StudentId and TestNumber fields.

constraint_type     constraint_keys                
======================= ==============================================
CHECK on column Score  ([Score] >= 0 and [Score] <= 100)       
FOREIGN KEY       StudentId                   
            REFERENCES TestScores.dbo.Students (StudentId)
PRIMARY KEY (clustered) StudentId, TestNumber             

sp_helpindex

The sp_helpindex stored procedure gives information about a table's indexes. The statement sp_helpindex Students generated the following output. This result describes the Student table's UNIQUE constraint on the LastName/FirstName field combination and the primary key on the StudentId field.

If you refer to the earlier "Test Database" section, you can examine the SQL script that created the TestScores database. The Students table's CREATE TABLE statement explicitly gives its UNIQUE constraint the name con_Students_Names. The sp_helpindex procedure correctly lists that index name.

The CREATE TABLE statement marked the StudentId field as the table's primary key, but did not name it. In cases like that, the database automatically creates an index name. In this case, it is named PK__Students__182C9B23. While distinctive, this is not a very memorable name. If you will need to explicitly manipulate an index later with your code, give it a more meaningful name when you create it.

index_name             index_description                                   index_keys     
====================== =================================================== ===================
con_Students_Names     nonclustered, unique, unique key located on PRIMARY FirstName, LastName
PK__Students__182C9B23 clustered, unique, primary key located on PRIMARY   StudentId     
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