1 CSE 480: Database Systems Lecture 10: SQL - DML Reference: Read Chapter 4 of the textbook

2 Review SQL DDL DML CREATEDROPALTER UPDATERETRIEVAL INSERTDELETEUPDATE SELECT FROM WHERE GROUP BY HAVING ORDER BY

3 SQL DML (Updates) l There are three SQL commands to update the database state –INSERT –DELETE –UPDATE

4 COMPANY Database Schema

5 INSERT l Add one or more tuples to a relation –Attribute values must be listed in the same order as the attributes specified in the CREATE TABLE command INSERT INTO EMPLOYEE VALUES ('Richard','K','Marini',' ','30-DEC-52', '98 Oak Forest,Katy,TX','M',37000,' ',4)

6 INSERT l An alternate form of INSERT specifies explicitly the attribute names that correspond to values in the new tuple –Attributes with NULL values can be left out INSERT INTO EMPLOYEE (FNAME, LNAME, SSN) VALUES ('Richard', 'Marini', ' ')

7 Disable Foreign Key in MySQL l Set foreign_key_checks = 0; l Useful to insert a tuple for subordinate before inserting the tuple for supervisor INSERT INTO EMPLOYEE (FNAME, LNAME, SSN, SUPER_SSN) VALUES ('Rob', ‘Stanley', ' ', ' ')

8 INSERT l Insertion of multiple tuples resulting from a query into a relation –Example: Suppose we want to create a temporary table that has the name, number of employees, and total salaries for each department. CREATE TABLE DEPTS_INFO (DEPT_NAMEVARCHAR(10), NO_OF_EMPSINTEGER, TOTAL_SALINTEGER); INSERT INTO DEPTS_INFO (DEPT_NAME, NO_OF_EMPS, TOTAL_SAL) SELECTDNAME, COUNT (*), SUM (SALARY) FROMDEPARTMENT, EMPLOYEE WHEREDNUMBER=DNO GROUP BYDNAME ;

9 DELETE l Removes tuples from a relation –Includes a WHERE-clause to select the tuples to be deleted l Examples: DELETE FROM EMPLOYEE WHERELname='Brown’; DELETE FROM EMPLOYEE WHERESSN=' ’; DELETE FROM EMPLOYEE WHEREDno IN (SELECT Dnumber FROM DEPARTMENT WHERE Dname='Research'); DELETE FROM EMPLOYEE;

10 UPDATE l Used to modify attribute values of one or more selected tuples UPDATE table_name SETset-clause WHERE where-clause –WHERE-clause selects the tuples to be modified –SET-clause specifies the attributes to be modified and their new values –Each command modifies tuples in the same relation

1 UPDATE l Example: Change the location and controlling department number of project number 10 to 'Bellaire' and 5, respectively UPDATE PROJECT SET PLOCATION = 'Bellaire', DNUM = 5 WHERE PNUMBER = 10

12 UPDATE Example: Give all employees in the 'Research' department a 10% raise in salary UPDATE EMPLOYEE SETSALARY = SALARY *1.1 WHEREDNO IN (SELECTDNUMBER FROMDEPARTMENT WHEREDNAME='Research')

13 Retrieval Queries in SQL l Basic form of the SQL retrieval queries: SELECT FROM WHERE – is a list of attribute names whose values are to be retrieved by the query – is a list of the relation names required to process the query – is a conditional (Boolean) expression that identifies the tuples to be retrieved by the query

14 Simple SQL Queries (from 1 Table) l Query: Retrieve the birthdate and address of the employee 'John B. Smith‘ SELECT FROM EMPLOYEE WHERE

15 Simple SQL Queries (from 1 Table) l Query: Retrieve the birthdate and address of the employee 'John B. Smith‘ SELECT Bdate, Address FROM EMPLOYEE WHERE

16 Simple SQL Queries (from 1 Table) l Query: Retrieve the birthdate and address of the employee 'John B. Smith‘ SELECT Bdate, Address FROM EMPLOYEE WHERE Fname='John' AND Minit='B' AND Lname='Smith';

17 Simple SQL Queries (from 1 Table) SELECT Bdate, Address FROM EMPLOYEE WHERE Fname='John' AND Minit='B' AND Lname='Smith'; For each row in Employee table If row.Fname='John' AND row.Minit='B' AND row.Lname='Smith' then print row.Bdate, row.Address Another way to interpret this:

18 Simple SQL Queries (from 1 Table) l Query: Retrieve the name and address of employees who work for department number 5 SELECT Fname, Lname, Address FROM Employee WHERE Dno = 5;

19 Simple SQL Queries (from 1 Table) l Query: Retrieve all the rows and columns in the Employee table SELECT * FROM Employee; Wildcard (*) in the SELECT clause means retrieve all columns No WHERE clause means all the rows will be retrieved

20 Simple SQL Queries (from 2 Tables) l Query: Retrieve the first name, last name and address of all employees who work for the 'Research' department

21 Join Operation l SQL uses JOIN operation to combine information from two or more tables IDName 1John 2Mary 3Bob IDDegree 1BS 2 2MS 3 R.IDS.IDR.NameS.Degree 11JohnBS 22MaryBS 22MaryMS 33BobMS Join on R. ID = S.ID R S

2 Join Operation IDName 1John 2Mary 3Bob IDDegree 1BS 2 2MS 3 R.IDS.IDR.NameS.Degree 11JohnBS 22MaryBS 22MaryMS 33BobMS Join on R. ID = S.ID R S In this case, a row in R is “merged” with a row in S if their IDs are the same SELECT * FROM R, S WHERE R.ID = S.ID

23 Simple SQL Queries (from 2 Tables) l Query: Retrieve the first name, last name and address of all employees who work for the 'Research' department SELECT FROM Employee, Department WHERE

24 Simple SQL Queries (from 2 Tables) l Query: Retrieve the first name, last name and address of all employees who work for the 'Research' department SELECT Fname, Lname, Address FROM Employee, Department WHERE

25 Simple SQL Queries (from 2 Tables) l Query: Retrieve the first name, last name and address of all employees who work for the 'Research' department SELECT Fname, Lname, Address FROM Employee, Department WHERE Dname='Research'

26 Simple SQL Queries (from 2 Tables) l Query: Retrieve the first name, last name and address of all employees who work for the 'Research' department SELECT Fname, Lname, Address FROM Employee, Department WHERE Dname='Research' AND Dnumber=Dno;

27 Simple SQL Queries (from 2 Tables) l Query: Retrieve the name of each project and the name of the department that controls it SELECT FROM Department, Project WHERE

28 Simple SQL Queries (from 2 Tables) l Query: Retrieve the name of each project and the name of the department that controls it SELECT Pname, Dname FROM Department, Project WHERE

29 Simple SQL Queries (from 2 Tables) l Query: Retrieve the name of each project and the name of the department that controls it SELECT Pname, Dname FROM Department, Project WHERE Dnum=Dnumber;

30 Exercise List the names of all employees and their corresponding department names

31 Exercise List the names of managers for each department

32 Simple SQL Queries (from 3 Tables) l Query: For every project located in 'Stafford', list the project number, controlling department number, and the department manager's last name, address, and birthdate SELECT FROMPROJECT, DEPARTMENT, EMPLOYEE WHERE

3 Simple SQL Queries (from 3 Tables) l Query: For every project located in 'Stafford', list the project number, controlling department number, and the department manager's last name, address, and birthdate SELECTPNUMBER, DNUM, LNAME, BDATE, ADDRESS FROMPROJECT, DEPARTMENT, EMPLOYEE WHERE

34 Simple SQL Queries (from 3 Tables) l Query: For every project located in 'Stafford', list the project number, controlling department number, and the department manager's last name, address, and birthdate SELECTPNUMBER, DNUM, LNAME, BDATE, ADDRESS FROMPROJECT, DEPARTMENT, EMPLOYEE WHERE PLOCATION='Stafford'

35 Simple SQL Queries (from 3 Tables) l Query: For every project located in 'Stafford', list the project number, controlling department number, and the department manager's last name, address, and birthdate SELECTPNUMBER, DNUM, LNAME, BDATE, ADDRESS FROMPROJECT, DEPARTMENT, EMPLOYEE WHERE PLOCATION='Stafford‘ AND DNUM=DNUMBER AND MGRSSN=SSN;

36 Aliases l If a query refers to two or more attributes with the same name but in different relations, we must qualify the attribute name with the relation name by prefixing the relation name to the attribute name IDName 1John 2Mary 3Bob IDDegree 1BS 2 2MS 3 R.IDS.IDR.NameS.Degree 11JohnBS 22MaryBS 22MaryMS 33BobMS R S SELECT * FROM R, S WHERE R.ID = S.ID What if we want to join the same table? Use tuple variables

37 Tuple Variables l Query: For each employee, retrieve the employee's name and the name of his or her immediate supervisor SELECT FROM EMPLOYEE E, EMPLOYEE S WHERE  E and S are tuple variables

38 Tuple Variables l Query: For each employee, retrieve the employee's name and the name of his or her immediate supervisor SELECTE.FNAME, E.LNAME, S.FNAME, S.LNAME FROM EMPLOYEE E, EMPLOYEE S WHERE  E and S are tuple variables

39 Tuple Variables l Query: For each employee, retrieve the employee's name and the name of his or her immediate supervisor SELECTE.FNAME, E.LNAME, S.FNAME, S.LNAME FROM EMPLOYEE E, EMPLOYEE S WHEREE.SuperSSN = S.SSN  E and S are tuple variables

40 Exercise l Query: Find the names of employees who earn more than their supervisors SELECT E.FNAME, E.LNAME FROM EMPLOYEE E, Employee S WHERE E.SUPERSSN=S.SSN AND E.SALARY > S.SALARY;

41 Find the names of the department where John Smith is currently working. SELECT DNAME FROM EMPLOYEE, DEPARTMENT WHERE DNO=DNUMBER and FNAME=‘John’ and LNAME=‘Smith’ Find names of the managers earning more than 100K SELECT FNAME, LNAME FROM EMPLOYEE, DEPARTMENT WHERE DNO=DNUMBER and MGRSSN=SSN and SALARY> Find names of employees worked on multiple (at least 2) projects. SELECT name FROM EMPLOYEE A, EMPLOEE B, DEPARTMENT C, DEPARTMENT D WHERE A.SSN = B.SSN AND C.DNUM not= D.DNUM OR SELECT FNAME, LNAME FROM EMPLOYEE WHERE (SELECT COUNT(*) FROM PROJECT WHERE DNO=DNUM) >= 2 A MORE GENERAL METHOD LATER