Article: Q180841
Product(s): Microsoft C Compiler
Version(s): 2000,5.0,6.0,7.0,97
Operating System(s):
Keyword(s): kbole kbAccess kbAccess97 kbJET kbMDAC kbMFC kbVC500 kbVC600 kbGrpDSVCDB kbGrpDSMDAC kb
Last Modified: 23-AUG-2001
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The information in this article applies to:
- The DAO SDK, used with:
- Microsoft Visual C++, 32-bit Enterprise Edition, version 5.0
- Microsoft Visual C++, 32-bit Professional Edition, version 5.0
- Microsoft Visual C++, 32-bit Enterprise Edition, version 6.0
- Microsoft Visual C++, 32-bit Professional Edition, version 6.0
- Microsoft Visual C++, 32-bit Learning Edition, version 6.0
- The Microsoft Foundation Classes (MFC)
- Microsoft Access 2000
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SUMMARY
=======
This article demonstrates some common DDL (Data Definition Language) SQL
statements for the Microsoft Jet database engine.
MORE INFORMATION
================
Microsoft Jet provides a full set of Data Definition Language SQL statements,
which can be used to create, modify, and delete tables, indexes, and
relationships in a Microsoft Access database file. You can use this DDL with the
MFC database classes to manipulate an Access database. This article lists some
common examples of this category of SQL statements.
You can execute a single DDL statement in this article using the following syntax
with the MFC DAO classes:
// Open database file.
CDaoDatabase db;
db.Open( _T("C:\\MyDatabase.mdb") );
// Set strSQL to desired DDL statement.
CString strSQL;
strSQL = _T("CREATE TABLE Simple (ID long)" );
// Execute DDL statement.
try
{
db.Execute( strSQL, dbFailOnError );
}
catch ( CDaoException *e )
{
// Display errors (simple example).
AfxMessageBox( e->m_pErrorInfo->m_strDescription,
MB_ICONEXCLAMATION );
e->Delete();
}
You can execute the DDL statements in this article using the following syntax
with the MFC ODBC classes:
// Open database file.
CDatabase db;
db.OpenEx( _T("DSN=MyAccessDB"), CDatabase::noOdbcDialog );
// Set strSQL to desired DDL statement.
CString strSQL;
strSQL = _T("CREATE TABLE Simple (ID long)" );
// Execute DDL statement.
try
{
db.ExecuteSQL( strSQL );
}
catch ( CDBException *e )
{
// Display errors (simple example).
AfxMessageBox( e->m_strError,
MB_ICONEXCLAMATION );
e->Delete();
}
The CREATE TABLE DDL Statement
------------------------------
The following create table statement creates a test table with all of the DDL
available to Microsoft Access data types:
CREATE TABLE TestAllTypes
(
MyText TEXT(50),
MyMemo MEMO,
MyByte BYTE,
MyInteger INTEGER,
MyLong LONG,
MyAutoNumber COUNTER,
MySingle SINGLE,
MyDouble DOUBLE,
MyCurrency CURRENCY,
MyReplicaID GUID,
MyDateTime DATETIME,
MyYesNo YESNO,
MyOleObject LONGBINARY,
MyBinary BINARY(50)
)
Note: You cannot create "AutoNumber Replication," "HyperLink," or "Lookup" type
fields using a Microsoft Access DDL SQL statement. These field types are not
native Jet field types and can be created and used only by the Microsoft Access
user interface. The MyBinary field above is a special fixed-length binary field,
which cannot be created via the Microsoft Access user interface but can be
created using a SQL DDL statement.
You can create a table with a single-field primary key with a single DDL
statement. The following statement creates a table named TestPrimaryKey with a
primary key on the MyID field named PK_MyID:
CREATE TABLE TestPrimaryKey
(
MyID LONG CONSTRAINT PK_MyID PRIMARY KEY,
FirstName TEXT(20),
LastName TEXT(20)
)
The ALTER TABLE DDL Statement
-----------------------------
Microsoft Access DDL supports the ALTER TABLE DDL statement. This statement is
useful when you need to remove or add a field to an existing table.
Note: This statement won't let you alter an existing field in an Access table
(for example, to change the field's data type).
The following DDL removes the column named MoreInfo from the table
TooManyFields:
ALTER TABLE TooManyFields DROP COLUMN MoreInfo
The following DDL statement adds a column named ExtraInfo to a table named
NotEnoughFields:
ALTER TABLE NotEnoughFields ADD COLUMN ExtraInfo Text(255)
The ALTER TABLE statement can also be used to create a relationship between two
tables.
The following SQL statement creates two tables (Cars and Colors) and then creates
a relationship between the Cars table and the Colors table on the ColorID field
(each car can have only one color).
Note: There are three separate DDL statements, which must be executed one at a
time:
CREATE TABLE Cars
(
CarID LONG,
CarName TEXT(50),
ColorID LONG
)
CREATE TABLE Colors
(
ColorID LONG CONSTRAINT PK_Colors PRIMARY KEY,
ColorName TEXT(50)
)
ALTER TABLE Cars
ADD CONSTRAINT MyColorIDRelationship
FOREIGN KEY (ColorID) REFERENCES Colors (ColorID)
Note: You cannot specify that you want "Cascade Updates" or "Cascade Deletes"
with a relationship created using DDL. These features are available only when
using the Microsoft DAO (Data Access Objects) interfaces via code or when using
the Microsoft Access user interface.
The CREATE INDEX DDL Statement
------------------------------
The CREATE INDEX DDL statement is used to create additional indexes on an
existing table.
The following DDL statement adds a single-field, non-unique, ascending index
named MyStateIndex to the field State in the table Addresses:
CREATE INDEX MyStateIndex
ON Addresses
(
State ASC
)
The following DDL statement adds a two-field, unique, ascending index named
MyFullNameIndex to the fields FirstName and LastName in the table Addresses:
CREATE UNIQUE INDEX MyFullNameIndex
ON Addresses
(
FirstName ASC,
LastName ASC
)
You can also specify an additional constraint of DISALLOW NULL using the CREATE
TABLE DDL statement. Specifying DISALLOW NULL means that the index will prevent
the insertion of fields with null values into any of the columns in the index.
The following DDL statement creates a single-field, unique, descending index
named MySalaryIndex on the field Salary in the table HRInfo:
CREATE UNIQUE INDEX MySalaryIndex
ON HRInfo
(
Salary DESC
)
WITH DISALLOW NULL
This index enforces that every record must have a value for the Salary field.
The DROP DDL Statement
----------------------
The DROP DDL statement is used to delete existing tables or indexes.
The following DDL statement permanently deletes the table named TempTable:
DROP TABLE TempTable
The following DDL statement permanently deletes the index named MyUnusedIndex on
the table OverIndexedTable:
DROP INDEX MyUnusedIndex ON OverIndexedTable
REFERENCES
==========
For more information about the Microsoft Jet DDL syntax, refer to the "Microsoft
Jet Database Engine Programmer's Guide, Second Edition," Chapter 3, "Data
Definition and Integrity."
Additional query words: kbAccess700 kbdse
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Keywords : kbole kbAccess kbAccess97 kbJET kbMDAC kbMFC kbVC500 kbVC600 kbGrpDSVCDB kbGrpDSMDAC kbDSupport MSGRAPH kbMDAC250 kbMDAC260
Technology : kbAudDeveloper kbDAOsearch kbSDKDAOSearch kbSDKSearch
Version : :2000,5.0,6.0,7.0,97
Issue type : kbhowto
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