Refining the Server Model

Adding New Tables New Table New View New Snapshot New Cluster New Column New Man FK New Opt FK

Add a Foreign Key

Create Index for FK DDT Automatically Creates Index for FK

Other Columns to Index Key columns Columns used frequently in queries Columns with many distinct values Guidelines: –Start with the least number of indexes –Add indexes as the data grows –Check both query and DML perfomance

Choosing the Number of Indexes More indexes = slower insert and delete Concatenated indexes can help Queries: NAME = 'SMITH'; JOB LIKE 'SALES%' AND NAME = 'SMITH'; JOB = 'CLERK' AND NAME = 'SMITH' AND HIREDATE > '1-JUN-98'; HIREDATE = '31-DEC-98'; Indexes: NAMEJOBHIREDATE NAME JOB HIREDATE

Oracle Sequence Database object: –Generates unique numbers –Minimizes contention Gaps in sequence 3 2 1

Adding Surrogate Key Create a Sequence Assign to Column Create Key

DDT Surrogate Keys Automatically creates key Automatically creates sequence Automatically assigns sequence to key column

Oracle Sequences Efficient Have Gaps –Rolled back transactions do not return used sequence numbers

Eliminating the Gaps IDENTIFIERLAST_NAME New row SMITH HAMBURG CG_CODE_CONTROLS EMPLOYEES CC_DOMAIN CC_NEXT VALUE CC_INCREMENT EMP_SEQ EMP_SEQ1 1 CC_DOMAIN CC_NEXT VALUE CC_INCREMENT EMP_SEQ EMP_SEQ1 1

Creating a Code Control Sequence Sequence Definitions Create Sequence: Name ? Name of the sequence Purpose of the sequence Sequence typeORACLE sequence Code control sequence 1 2 3

RE_IDLINE_NO RENTAL_ITEMS Sequence Within Parent RE_ID 1212 RENTALS Generate a value within the context of the parent record

Creating a Sequence Within a Parent Set AutoGen Type to Seq in Parent Column Properties Derivation Autogen Type … Seq in Parent

Choosing a Method Oracle sequence: –Sequential values with gaps –Recommended Code control sequence: –Databases other than Oracle –Sequential values without gaps –Contention can be tolerated Sequence within a parent: –Minimal number of detail records