1. CS122 Using Relational Databases and SQL
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CS122 Using Relational Databases and SQL
8. Data Manipulation and Definition
Daniel Firpo
Department of Computer Science
California State University, Los Angeles 1

2. Outline Data manipulation Data definition INSERT DELETE UPDATE
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Outline
Data manipulation
INSERT
DELETE
UPDATE
Data definition
CREATE a table
MODIFY a table
DELETE a table
8. Data Manipulation & Definition CS1222_F2018
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3. Database Definition Language (DDL)
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Database Definition Language (DDL)
Subset of SQL commands to create and modify database objects
Can create an entire database using SQL rather than a graphical user interface
With DDL you gain more control over exactly what database objects are built and what they are named
DDL saved into a script can be easily ported from one database installation to another
8. Data Manipulation & Definition CS1222_F2018

4. 8. Data Manipulation & Definition CS1222_F2018
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Naming Tips
Use consistent names
Do not include spaces inside your table or fields
Avoid the use of SQL reserved words and punctuation marks in table and field names 
Keep names short, but long enough to be descriptive
Be consistent in your use of abbreviations
Name primary key and foreign key fields consistently
Avoid generic field names, such as ID or Date
8. Data Manipulation & Definition CS1222_F2018

5. Databases
MySQL
Instance of MySQL running on a server computer can contain multiple databases
New MySQL database can be created with Create Database followed by the name to be used for the new database or Create Database If Not Exists followed by the name of the database
There are no other options for the Create Database command
Can switch between databases by typing Use followed by the database name

6. 8. Data Manipulation & Definition CS1222_F2018
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Creating a Table
Null means that the field may contain null (empty) values. Not Null means that the field cannot contain null values.
Syntax
CREATE TABLE tablename (
Fieldname1 DataType NULL | NOT NULL,
Fieldname2 DataType NULL | NOT NULL )
Please refer to earlier slides for datatypes in MySQL
8. Data Manipulation & Definition CS1222_F2018

7. Creating a Table: Example
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Create a table called Contracts with the ArtistID from the Artists table and a ContractDate field
CREATE TABLE tblContracts (
ArtistID Integer NOT NULL,
ContractDate DateTime NOT NULL )
A left parenthesis comes before the first field in the list. Each field entry except the last one is followed by a comma. The last field in the list is followed by a right parenthesis.
8. Data Manipulation & Definition CS1222_F2018

8. 8. Data Manipulation & Definition CS1222_F2018
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Dropping a Table
Syntax
DROP Table tablename
Example: Remove the tblContracts table from the database
DROP Table tblContracts
8. Data Manipulation & Definition CS1222_F2018

9. Adding Columns to an Existing Table
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Adding Columns to an Existing Table
Syntax
ALTER TABLE tablename
ADD fieldname DataType NULL | NOT NULL
8. Data Manipulation & Definition CS1222_F2018

10. Adding Columns to an Existing Table
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Adding Columns to an Existing Table
Add a text field called ContractType with a length of 10 to the tblContracts table
ALTER TABLE tblContracts
ADD ContractType VarChar(10) NULL
8. Data Manipulation & Definition CS1222_F2018

11. Altering Existing Columns in a Table
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Altering Existing Columns in a Table
Syntax
ALTER TABLE tablename
MODIFY fieldname DataType NULL | NOT NULL
8. Data Manipulation & Definition CS1222_F2018

12. Altering Existing Columns in a Table: Example
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Altering Existing Columns in a Table: Example
Change the length on the ContractType field to 15 in the tblContracts table
ALTER TABLE tblContracts
MODIFY ContractType VARCHAR(15) NULL
8. Data Manipulation & Definition CS1222_F2018

13. 8. Data Manipulation & Definition CS1222_F2018
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Dropping a Column
Syntax
ALTER TABLE tablename
DROP COLUMN columnname
Example: Remove the Contracttype column from the tblContracts table
ALTER TABLE tblContracts
DROP COLUMN ContractType
8. Data Manipulation & Definition CS1222_F2018

14. Identity Columns and Sequences
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Identity Columns and Sequences
Techniques to automatically generate a sequential number with each row that is inserted
Never have to insert a value to it, but it will always be unique within that table
Make excellent primary keys in cases where there is no naturally occurring primary key
8. Data Manipulation & Definition CS1222_F2018

15. Defining an Identity Column
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Defining an Identity Column
CREATE TABLE tblX (
ID INT auto_increment Primary key,
anotherfield int NULL )
8. Data Manipulation & Definition CS1222_F2018

16. Sequences Vs. Guid Columns
An identity column (or sequence) is unique within a given a table in a given database on a given server
With distributed database, identity column may not\be unique across every instance of the table
One solution is to use the identity column in conjunction with a locationID as the primary key
Another solution Globally Unique Identifier (GUID), which is supported in some databases
A GUID is a 16-byte ID guaranteed to be unique across every instance of a distributed database
GUIDs are cumbersome to work with: C1C5FCE2-879E-4A96-B845- 9F3FC4A10EC8