1. Dec 4, 2003Murali Mani SQL B term 2004: lecture 14

2. Dec 4, 2003Murali Mani Inserting tuples INSERT INTO Student VALUES (6, ‘Emily’, ‘324 FL’, NULL); INSERT INTO Student (sNumber, sName) VALUES (6, ‘Emily’); INSERT INTO Student (sNumber, sName) SELECT pNumber, pName FROM Professor;

3. Dec 4, 2003Murali Mani Delete and Update Deleting tuples DELETE FROM Student WHERE sNumber=‘6’; Updating tuples UPDATE Student SET professor=‘ER’ WHERE sNumer=‘6’

4. Dec 4, 2003Murali Mani SQL DDL (Data Definition Language) Creating table CREATE TABLE Student ( sNumber integer, sName varchar (20), address varchar (30), professor char (2), gender char (1) DEFAULT ‘?’);

5. Dec 4, 2003Murali Mani SQL DDL Dropping a table DROP TABLE Student; Altering a table ALTER TABLE Student DROP gender; ALTER TABLE Student ADD gender char (1); ALTER TABLE Student ADD gender char (1) DEFAULT ‘?’;

6. Dec 4, 2003Murali Mani Indexes Creation of indexes is NOT part of SQL However “common syntax” is used. CREATE INDEX ON (a1, a2, …, an) For eg: CREATE INDEX NameDeptIndex ON Student (sname, dept) In oracle, you can see the indexes are stored in a table “user_ind_columns” SELECT * FROM user_ind_columns; DROP INDEX

7. Dec 4, 2003Murali Mani Indexes: Illustration Indexes make queries faster, they might make modifications longer. As an example, let us consider Student (sNumber, sName, dept) Let us assume a disk block can hold 2 data records. Let us assume there are 3 data records for each sName, and there are 9 data records in total.

8. Dec 4, 2003Murali Mani Indexes: Illustration Empty Dave Greg Amanda

9. Dec 4, 2003Murali Mani Indexes: Illustration SELECT * FROM Student where student=“Amanda” – 4 disk accesses Inserting a new student with name=“Amanda” – 4 disk accesses. Note assumption: given Amanda, we know the index block with 0 disk access. We know the “unfull” data block with 0 disk access.

10. Dec 4, 2003Murali Mani Views View is a virtual relation Convenience: Queries on base relations might be “complex” Independence: “base tables” may change, but still queries using views need not change. CREATE VIEW as CREATE VIEW studentProfessor (student, professor) AS SELECT sName, pName FROM Student, Professor WHERE Student.professor = Professor.pName; DROP VIEW

11. Dec 4, 2003Murali Mani Querying Views Views can be queried on just like a relation Some views can be updated, not all. “Idea”: View must be columns of one table such that updates to the view can be mapped to updates on the “base table” Enforced in SQL as: Updatable views are specified using SELECT (not SELECT DISTINCT) FROM should specify one relation R WHERE clause cannot involve R in subquery. SELECT clause must include enough attributes so that filling out the rest of the attributes as NULL in R does not violate any constraint.