SQL: DDL

SQL Statements• DDL - data definition language

– Defining and modifying data structures (metadata): database, tables, views, etc.

• DML - data manipulation language– Manipulating user data: insert, update,

select, etc.

• DCL - data control language– Control data access: permissions, etc.

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SQL DDL• DDL statements include

– CREATE Table– ALTER Table– DROP Table

Create TableCREATE TABLE TableName(

ColumnDefinitions,Table Constraints

)

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Column Definition• What to define?

– Column name (required)– Data type and length (required)– Column constraints (optional): primary

key, null, not null, default, unique, check

• ExampleFirstName VARCHAR(30) NOT NULL,

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Data Types

• Data types are slightly different in many database products

• Data types reference– Access 2007: http://msdn.microsoft.com/en-us/library/bb208866.aspx– SQL Server 2005: http://msdn.microsoft.com/en-us/library/ms187752(SQL.90).aspx

Example

Example: Using Table Constraints

Example: Foreign Key

ALTER Table• Alter Table TableName

[Modification]

• Modification include– Add, modify, drop columns– Add, modify, drop table constraints

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Altering Columns• Adding a new column

ALTER TABLE tablenameADD (column datatype);

• Modify a column

ALTER TABLE tablenameMODIFY (column newdatatype);

ALTER TABLE CustomerADD (FNAME VARCHAR(30));ALTER TABLE CustomerADD (FNAME VARCHAR(30));

ALTER TABLE Customer MODIFY (FName VARCHAR(40));ALTER TABLE Customer MODIFY (FName VARCHAR(40));

Drop a column

ALTER TABLE tablenameDROP COLUMN colummname;

ALTER TABLE CustomerDROP COLUMN FName;ALTER TABLE CustomerDROP COLUMN FName;

Altering Table Constraints• Add a foreign key

Alter table GroupAssignment add constraint GroupAssignment_FK2 foreign key(GroupNumber)

references Groups(GroupId) on update cascade;

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DROP Table

DROP TABLE tablename;

DROP TABLE Customer;DROP TABLE Customer;

Warning… The DROP statement will permanently remove table structure and all data

Summary• Key concepts

– DDL– Create– Alter– Drop– SQL Data types– Referential integrity, cascade