1 Table Alteration

2 Altering Tables Table definition can be altered after its creation –Adding columns –Changing columns’ definition –Dropping columns –Adding constraints –And more… Use the reserved word ALTER

3 Altering Tables (continued) Adding a column: ALTER TABLE Employee ADD ( Mname VARCHAR2(20), Birthday DATE ); Changing columns ’ definition: ALTER TABLE Emplyee Modify ( Mname VARCHAR2(10) ); Cannot be NOT NULL unless the table is empty

4 Altering Tables (continues) Dropping columns: ALTER TABLE Employee DROP COLUMN Mname; Dropping multiple columns: ALTER TABLE Employee DROP (Mname, Birthday); Adding constraints: ALTER TABLE Department ADD( FOREIGN KEY (ManagerId) REFERENCES Employee(SSN));

5 User’s Table List ORACLE may print tables that hold some general information about the tables in your database Such Tables are: –Tab, Cat, User_Tables (too detailed...) To see the list of all your tables you can print: –SELECT * FROM Cat; –SELECT tname FROM Tab; –SELECT table_name from User_Tables;

6 Table Data Maintenance

7 The Employee Table > Describe Employee Name Null? Type SSN NUMBER FNAME VARCHAR2(20) LNAME VARCHAR2(20) GENDER CHAR(1) SALARY NOT NULL NUMBER(5)

8 Inserting a Row To insert a row into the Employee table: INSERT INTO Employee(SSN, Fname, Lname, Salary) VALUES(121, ‘Sara’, ‘Cohen’,10000); The remaining columns get default values (or NULL) When will this fail?

9 Some More Details… The fields needn’t be specified if values are specified for all columns and in the order defined by the table Example: INSERT INTO Employee VALUES(121, ‘Sara’, ‘Cohen’, `F’, 10000);

10 Deleting Rows General format: DELETE FROM Table WHERE Cond; Deletes all rows satisfying Cond from Table For example, to remove the employee with SSN 121 from the Employee table: DELETE FROM Employee WHERE SSN = 121;

11 Deleting Rows (continues) To remove all male employees having a salary greater than shekels: DELETE FROM Employee WHERE Gender = ‘M’ AND Salary > 15000; The WHERE clause is basically the same as one in a query Case sensitive

12 Updating Rows (continues) We can update fields of rows in a table General format: UPDATE Table SET Field1=value1,,,FieldN=valueN WHERE Cond Now we can reduce salaries instead of firing employees: UPDATE Employee SET Salary = WHERE Gender = ‘M’ AND Salary > 15000;

13 The ORACLE Bulk Loader A tool that provides easy insertion of large amounts of rows into tables. The idea: the field values of the rows are kept in a file, the format of which is defined by us. For example, it can automatically load 3 employees from the file myEmployees.dat that contains the following lines: Sara|Cohen|121 Benny|Kimelfeld|134 Yaron|Kanza|156

14 The Control File The control file is the direct input of the loader A simple control file: LOAD DATA INFILE [APPEND] INTO TABLE FIELDS TERMINATED BY ' ‘ ( )

15 The Control File (continued) : The name of the data file : The name of the table into which the data will be loaded (appended if APPEND is specified, or else the table must be empty) : A string that separates two field values of a row The attributes are separated by commas and enclosed in parentheses

16 The Control File (continues) As an example, the following control file loads the employees from myEmployees.dat: LOAD DATA INFILE myEmployees.dat INTO TABLE Employees FIELDS TERMINATED BY '|' (Fname, Lname, SSN) The attributes that are unspecified will be set to NULL

17 The Data File The Bulk Loader considers every single line to represent one row in the table –Even an empty line! (which will usually result in an error) Spaces are not ignored in the data file! – thus the rows sara| cohen|121 and sara|cohen|121 define different functionalities The NULL value is implied by the NULL keyword or the empty string

18 The Data File (continued) The control and the data files can be combined into one.ctl file using the following format: LOAD DATA INFILE * INTO TABLE Employees FIELDS TERMINATED BY '|' (Fname, Lname, SSN) BEGINDATA Sara|Cohen|121 Benny|Kimelfeld|134 Yaron|Kanza|156

19 The Bulk Invocation To invoke the bulk loader, issue the following command directly from the Unix shell: sqlldr control= log= bad= –All fields are optional –File names that have no extension are automatically extended (by.dat,.log or.bad) Erroneous lines in the data file are ignored and written into badFile, and any other relevant information is written into logFile.

20 Bulk Loader Important Remarks Before using the Bulk Loader, make sure your personal ORACLE environment is properly set up The tables you fill using the Bulk Loader should be created prior to the loader invocation Before invoking the Bulk Loader you have to make sure that NO SQLPLUS SESSIONS ARE OPEN!

21 SQL Queries

22 Query Components A query can contain the following clauses –select –from –where –group by –having –order by Only select and from are required Order of clauses is always as above

23 Basic SQL Query SELECT [Distinct] Attributes FROM relations WHERE condition; Attributes: A list of fields onto which the query projects (For example: Eid, Ename). relations: A list of relation names (For example: Employees, Departments, Works). condition: A Boolean condition (For example: Eid>21, or Ename=‘Yuval’ ) DISTINCT: Optional keyword to delete duplicates

24 Basic SQL Query SELECT [Distinct] attributes FROM relations WHERE condition; Notice! The "SELECT" clause defines the operation of projection from the relational model. Selection is defined by the WHERE clause.

25 Basic SQL Query SELECT [Distinct] attributes FROM relations WHERE condition; Evaluation order: 1.Compute the cross product of the tables in relations. 2.Delete all rows that do not satisfy condition. 3.Delete all columns that do not appear in attributes. 4.If Distinct is specified eliminate duplicate rows.

26 Basic SQL Query SELECT Distinct A 1,…,A n FROM R 1,…,R m WHERE C;  A 1,…,A n (  C (R 1 x…x R m ))

27 Query Without WHERE SELECT Distinct A 1,…,A n FROM R 1,…,R m  A 1,…,A n (R 1 x…x R m )

28 Query Without Projection SELECT Distinct * FROM R 1,…,R m WHERE C; (  C (R 1 x…x R m ))

29 Query Without Projection, Without WHERE SELECT Distinct * FROM R 1,…,R m R 1 x…x R m

30 Example Tables Used Reserves sidbidday /10/96 11/12/96 Sailors sidsnameratingage Dustin Lubber Rusty Boats bidbnamecolor Nancy Gloria red green

31 Example Query SELECT DISTINCT sname, age FROM Sailors WHERE rating>7; Q: What does this compute? A: Distinct names and ages of sailors with a rating >7. Q: Write it in algebra A:  sname, age (  rating>7 (Sailors)) When would the result be different if we removed distinct?

32 Example Query SELECT DISTINCT sname FROM Sailors, Reserves WHERE Sailors.sid = Reserves.sid and bid = 103; Q: What does this compute? A: names of sailors who reserved boat 103 Q: Write it in relational algebra  sname (  Sailors.sid = Reserves.sid  bid = 103 (Sailors x Reserves))

33 SailorsReserves sidsnameratingagesidbidday 22Dustin /10/96 22Dustin /12/96 31Lubber /10/96 31Lubber /12/96 58Rusty /10/96 58Rusty /12/96 Sailors x Reserves

34 SailorsReserves sidsnameratingagesidbidday 22Dustin /10/96 22Dustin /12/96 31Lubber /10/96 31Lubber /12/96 58Rusty /10/96 58Rusty /12/96  Sailors.sid = Reserves.sid  bid = 103

35 SailorsReserves sidsnameratingagesidbidday 22Dustin /10/96 22Dustin /12/96 31Lubber /10/96 31Lubber /12/96 58Rusty /10/96 58Rusty /12/96 Sailors x Reserves  sname

36 Range Variables SELECT S.sname FROM Sailors S, Reserves R WHERE S.sid = R.sid and R.bid = 103; Range variables are good style. They are necessary if the same relation appears twice in the FROM clause Similar to Renaming in Relational Algebra

37 Example Query SELECT S.sname FROM Sailors S, Reserves R WHERE S.sid = R.sid and R.bid != 103; Q: What does this return? A: Names of sailors who reserved a boat other than boat 103 Notice: sailors who reserved both boat 103 and a different boat will appear!

38 A Few SELECT Options Select all columns: SELECT * FROM Sailors S; Rename selected columns: SELECT S.sname AS Sailors_Name FROM Sailors S; Applying functions (e.g., Mathematical manipulations) SELECT (age-5)*2 FROM Sailors S;

39 The WHERE Clause Numerical and string comparison: !=,<>,=,, >=, <=, between(between val1 AND val2) Logical components: AND, OR Null verification: IS NULL, IS NOT NULL Checking against a list with IN, NOT IN.

40 Examples SELECT sname FROM Sailors WHERE age>=40 AND rating IS NOT NULL ; SELECT sid, sname FROM sailors WHERE sid IN (1223, 2334, 3344) or sname between(‘George’ and ‘Paul’);

41 The LIKE Operator A pattern matching operator Basic format: colname LIKE pattern –Example: _ is a single character % is 0 or more characters SELECT sid FROM Sailors WHERE sname LIKE ‘R_%y’;

42 SQL query SELECT S.sid FROM Sailors S, Reserves R WHERE S.sid = R.sid; When would adding DISTINCT give a different result?

43 Are any of these the same? SELECT S.sid FROM Sailors S, Reserves R WHERE S.sid = R.sid; SELECT DISTINCT R.sid FROM Sailors S, Reserves R WHERE S.sid = R.sid; SELECT R.sid FROM Reserves R

44 Example Query SELECT S.sname FROM Sailors S, Reserves R1, Reserves R2. WHERE S.sid = R1.sid and R1.sid=R2.sid and R1.bid!=R2.bid; How would you query sailors who have reserved more than one boat?

45 SQL query SELECT S.sname FROM Sailors S, Reserves R, Boats B WHERE S.sid = R.sid and R.bid = B.bid and B.color = 'red' Q: What does this return? A: Names of sailors who have reserved a red boat.

46 SQL query SELECT distinct B.color FROM Sailors S, Reserves R, Boats B WHERE S.sname = ‘Bob’ and S.sid = R.sid and R.bid = B.bid Q: How would you query the colors of boats reserved by Bob? A:

47 Order Of the Result The ORDER BY clause can be used to sort results by one or more columns The default sorting is in ascending order Can specify ASC or DESC

48 Example SELECT sname, rating, age FROM Sailors S WHERE age > 50 ORDER BY rating ASC, age DESC

49 Other Relational Algebra Operators So far, we have seen selection, projection and Cartesian product How do we do operators UNION and MINUS?

50 Three SET Operators [Query] UNION [Query] [Query] MINUS [Query] [Query] INTERSECT [QUERY] Note: The operators remove duplicates by default! How would you express intersect in Relational Algebra?

51 What does this return? SELECT DISTINCT S.sname FROM Sailors S, Reserves R, Boats B WHERE S.sid = R.sid and R.bid = B.bid and (B.color = 'red' or B.color='green') What would happen if we replaced or by and ?

52 Sailors who’ve reserved red or green boat SELECT S.sname FROM Sailors S, Boats B, Reserves R WHERE S.sid = R.sid and R.bid = B.bid and B.color = ‘red’ UNION SELECT S.sname FROM Sailors S, Boats B, Reserves R WHERE S.sid = R.sid and R.bid = B.bid and B.color = ‘green’; Would INTERSECT here give us sailors who reserved both red and green boats?

53 Sailors who’ve reserved red and green boats SELECT S.sname FROM Sailors S, Reserves R1, Reserves R2 Boats B1, Boats B2, WHERE S.sid = R1.sid and R1.bid = B1.bid and B1.color = ‘red’ and S.sid = R2.sid and R2.bid = B2.bid and B2.color = ‘green’;

54 Multiset (Bag) Operators SQL standard includes 3 bag operators: –UNION ALL –INTERSECT ALL –MINUS ALL Oracle supports only UNION ALL. Does not remove duplicates when performing UNION

55 Example SELECT DISTINCT sname FROM Sailors S UNION ALL SELECT DISTINCT sname FROM Sailors S

56 Nested Queries

57 Nested queries in WHERE Equality nested query: Select R.bid From Sailors S, Reserves R Where sid = (select sid from S where sname=‘George’); When would this work? When wouldn’t it?

58 Nested queries in WHERE SELECT S.sname FROM Sailors S WHERE S.sid IN (SELECT R.sid FROM Reserves R WHERE R.bid = 103); Subqueries with multiple results: Names of sailors who’ve reserved boat 103 What would happen if we wrote NOT IN?

59 What does this produce? SELECT S.sname FROM Sailors S WHERE S.sid NOT IN (SELECT R.sid FROM Reserves R WHERE R.bid IN (SELECT B.bid FROM Boats B WHERE B.color='red'))

60 Set-Comparison Queries SELECT * FROM Sailors S1 WHERE S1.age > ANY (SELECT S2.age FROM Sailors S2); Sailors who are not the youngest: We can also use op ALL (op is >, =, ).

61 Correlated Nested Queries SELECT S.sid FROM Sailors S WHERE EXISTS (SELECT * FROM Reserves R WHERE R.bid = 103 and S.sid = R.sid); Names of sailors who’ve reserved boat 103: What would happen if we wrote NOT EXISTS? S not in subquery, refers to outer loop

62 Exists and Not Exists Differ from In and Not In by not matching attributes. Exists: For every tuple in the outer loop, the inner loop is tested. If the inner loop produces a result, the outer tuple is added to the result.