1 reminder we have covered: –creating tables –converting er diagrams to table definitions today...

1

ReminderReminder

• We have covered:

– Creating tables

– Converting ER diagrams to table definitions

• Today we’ll talk about:

– Altering tables

– Inserting and deleting data from tables

– Querying tables

2

Table AlterationTable Alteration

3

Altering TablesAltering Tables

• Table definitions can be altered after their

creation

– Adding columns

– Changing columns’ definition

– Dropping columns

– Adding or dropping constraints

– And more…

• Use the reserved word ALTER

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Altering Tables (cont.)Altering Tables (cont.)

• 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

5

Altering Tables (cont.)Altering Tables (cont.)

• 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));

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Inserting, deleting, and Inserting, deleting, and updating data in a tableupdating data in a table

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The Employee TableThe 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 RowInserting 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…Some More Details…

• The fields don’t have to 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’, 1000);

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Deleting RowsDeleting 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;

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Deleting Rows (cont.)Deleting Rows (cont.)

• To remove all male employees having

a salary greater than 150,000 shekels:

DELETE FROM Employee

WHERE Salary > 150000;

12

Updating Rows Updating Rows

• We can update rows in a table• General format:

UPDATE Table SET Field1=value1,,,FieldN=valueNWHERE Cond

• Now we can reduce salaries instead of firing employees:

UPDATE Employee SET Salary = 50000 WHERE Salary > 150000;

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The ORACLE Bulk LoaderThe ORACLE Bulk Loader• A tool that provides easy insertion of large

amounts of rows into tables.• The idea: the values of the inserted rows are

kept in a compact file: the Data file.• We define the structure of the Data file, in

the Control file.

Here we enter the data we want to

insert (employees)

myData.dat

Here we specify the structure of

the data file

myCtrl.ctl

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The Control FileThe Control File

• For example, we can load 3 employees from the file myEmp.dat that contains the following lines:

Shaquile|Oneil|121Magic|Johnson|134Doron|Sheffer|156

• A simple control file:

LOAD DATA

INFILE <dataFile>

[APPEND] INTO TABLE <tableName>

FIELDS TERMINATED BY '<separator>‘

(<list of all attribute names to load>)

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The Control File (cont.)The Control File (cont.)

• <dataFile>:

The name of the data file

• <tableName>:

The name of the table into which the data will be loaded (appended if APPEND is specified, or else the table must be empty)

• <separator>:

A string that separates two field values of a row

• The attributes are separated by commas and enclosed in parentheses

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The Control File (cont.)The Control File (cont.)• Example:

– When the control file is run, this will insert the 3 employees into the employees table

– The attributes that are unspecified will be set to NULL (or default values if they are specified)

LOAD DATA

INFILE myEmployees.dat

INTO TABLE Employees

FIELDS TERMINATED BY '|'

(Fname, Lname, SSN)

Moshe|Cohen|334

Miri|Levi|998

Alon|Hazan|998

myEmployees.dat

myControl.ctl

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The Data FileThe 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

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The Data File (continued)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

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The Bulk InvocationThe Bulk Invocation

• To invoke the bulk loader, issue the following command directly from the Unix shell:Sqlldr <ctrlFileName>

• Erroneous lines in the data file are ignored and written into <ctrlFileName>.bad, and any other relevant information is written into <ctrlFileName>.log.

• 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.

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SQL QueriesSQL Queries

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Query ComponentsQuery 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

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Very Basic SQL QueryVery Basic SQL QuerySELECT [Distinct] Attributes

FROM relation

•Attributes: A list of attributes onto which the query projects (For example: Eid, Ename).

•Relation: A relation to perform the query on.

•DISTINCT: Optional keyword to delete duplicatesExample:

Select studentID, studentName

From students

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StudentIDStudentDe

pt.

StudentNa

me

StudentAg

e

1123 Math Moshe 25

2245 Computers Mickey 26

55611 Math Menahem 29

Select studentID, studentName

From students

Result:

StudentIDStudentNa

me

1123 Moshe

2245 Mickey

55611 Menahem

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Basic SQL QueryBasic SQL Query

SELECT [Distinct] Attributes

FROM relation

WHERE condition

•Attributes: A list of fields onto which the query projects (For example: Eid, Ename).

•relation: A relation to perform the query on

•condition: A Boolean condition (For example: Eid>21, or Ename=‘Yuval’ )

•DISTINCT: Optional keyword to delete duplicates

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StudentIDStudentDe

pt.

StudentNa

me

StudentAg

e

1123 Math Moshe 25

2245 Computers Mickey 26

55611 Math Menahem 29Select studentID, studentName

From students

Where StudentDept=‘Math’

Result:

StudentIDStudentNa

me

1123 Moshe

55611 Menahem

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Basic SQL QueryBasic SQL Query

SELECT [Distinct] attributes

FROM relation

WHERE condition;

•Notice! The "SELECT" clause defines the operation of projection from the relational model. Selection is defined by the WHERE clause.

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SQL and relational algebraSQL and relational algebra

SELECT Distinct A1,…,An

FROM R1,…,Rm

WHERE C;

A1,…,An (C(R1 x…x Rm))

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Basic SQL QueryBasic SQL Query

SELECT [Distinct] Attributes

FROM relationsList

WHERE condition

•relationsList: A list of relations. The query is performed on the product of these relations (AxBxC…).

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Basic SQL QueryBasic SQL Query

SELECT [Distinct] attributes

FROM relations

WHERE condition;

Important! The evaluation order is:

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.

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Example Tables UsedExample Tables Used

Reserves

sid bid day

22

58

101

103

10/10/96

11/12/96

Sailors

sid sname rating age

22

31

58

Dustin

Lubber

Rusty

7

8

10

45.0

55.5

35.0

Boats

bid bname color

101

103

Nancy

Gloria

red

green

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What does this compute?What does this compute?

Select sname

from sailors, reserves

Where sailors.sid=reserves.sid

Reserves

sid bid day

22

58

101

103

10/10/96

11/12/96

Sailors

sid sname rating age

22

31

58

Dustin

Lubber

Rusty

7

8

10

45.0

55.5

35.0

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Sailors Reserves

sid sname rating age sid bid day

22 Dustin 7 45.0 22 101 10/10/96

22 Dustin 7 45.0 58 103 11/12/96

31 Lubber 8 55.5 22 101 10/10/96

31 Lubber 8 55.5 58 103 11/12/96

58 Rusty 10 35.0 22 101 10/10/96

58 Rusty 10 35.0 58 103 11/12/96

Stage 1: Sailors x Reserves

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Sailors Reserves

sid sname rating age sid bid day

22 Dustin 7 45.0 22 101 10/10/96

22 Dustin 7 45.0 58 103 11/12/96

31 Lubber 8 55.5 22 101 10/10/96

31 Lubber 8 55.5 58 103 11/12/96

58 Rusty 10 35.0 22 101 10/10/96

58 Rusty 10 35.0 58 103 11/12/96

Stage 2: “where sailors.sid=reserves.sid”

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Sailors Reserves

sid sname rating age sid bid day

22 Dustin 7 45.0 22 101 10/10/96

58 Rusty 10 35.0 58 103 11/12/96

Stage 2: “where sailors.sid=reserves.sid”

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Sailors Reserves

sid sname rating age sid bid day

22 Dustin 7 45.0 22 101 10/10/96

58 Rusty 10 35.0 58 103 11/12/96

Stage 3: “select sname”

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Sailors

sname

Dustin

Rusty

Stage 3: “select sname”

Final answer

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Example QueryExample Query

SELECT DISTINCT sname, age

FROM Sailors

WHERE rating>7;

Q: What does this compute?

A: Distinct names and ages of sailors with rating >7.

Q: Write it in algebra

A: sname, age (rating>7(Sailors))

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Example QueryExample QuerySELECT 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))

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Sailors Reserves

sid sname rating age sid bid day

22 Dustin 7 45.0 22 101 10/10/96

22 Dustin 7 45.0 58 103 11/12/96

31 Lubber 8 55.5 22 101 10/10/96

31 Lubber 8 55.5 58 103 11/12/96

58 Rusty 10 35.0 22 101 10/10/96

58 Rusty 10 35.0 58 103 11/12/96

Sailors.sid = Reserves.sid bid = 103

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Sailors Reserves

sid sname rating age sid bid day

22 Dustin 7 45.0 22 101 10/10/96

22 Dustin 7 45.0 58 103 11/12/96

31 Lubber 8 55.5 22 101 10/10/96

31 Lubber 8 55.5 58 103 11/12/96

58 Rusty 10 35.0 22 101 10/10/96

58 Rusty 10 35.0 58 103 11/12/96

Sailors x Reserves

sname

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Range VariablesRange 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

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Example QueryExample Query

SELECT S.sname

FROM Sailors S, Reserves R

WHERE S.sid = R.sid and

R.bid != 103;

Q: What does this return?Q: What does this return?

A: Names of sailors who reserved a boat A: Names of sailors who reserved a boat other than boat 103 other than boat 103

Notice: sailors who reserved both boat 103 Notice: sailors who reserved both boat 103 andand a different boat will appear! a different boat will appear!

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A Few SELECT OptionsA Few SELECT Options

• Select all columns:SELECT * FROM Sailors;

• 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;

44

Select operatorsSelect operators

• The aggregate operators available in SQL are:

– COUNT(*)

– COUNT([DISTINCT] A)

– SUM([DISTINCT] A)

– AVG([DISTINCT] A)

– MAX(A)

– MIN(A)

• NULL values are ignored

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ExamplesExamples

SELECT Avg(S.age)

FROM Sailors S, Reserves R

WHERE S.sid = R.sid and R.bid=112

SELECT count(distinct S.sid)

FROM Sailors S, Reserves R

WHERE S.sid = R.sid

SELECT Max(S.age)

FROM Sailors S

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TheThe WHEREWHERE ClauseClause

• Numerical and string comparison:

!=,<>,=, <, >, >=, <=, between(val1 AND val2)

• Logical components: AND, OR

• Null verification: IS NULL, IS NOT NULL

• Checking against a list with IN, NOT IN.

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ExamplesExamples

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’);

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User’s Table ListUser’s Table List

• ORACLE holds tables with some general information

about the tables in your database

• Such Tables are:

– Cat, user_objects

• To see the list of all your tables print:

SELECT * FROM Cat;

• To see the list of all your objects print:

SELECT object_name, timestamp,

object_type FROM user_objects;

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The LIKE OperatorThe LIKE Operator

• A pattern matching operator (regular expression)

• Basic format: colname LIKE pattern– Example:

_ is a single character

% is 0 or more characters

SELECT sid FROM Sailors WHERE sname LIKE ‘R_%y’;

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SQL querySQL query

SELECT S.sid

FROM Sailors S, Reserves R

WHERE S.sid = R.sid;

When would adding DISTINCT give a different result?

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Are any of these the same?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

Sailors

sid sname rating age

Reserves

sid bid day

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Example QueryExample 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?

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SQL querySQL querySELECT 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.

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SQL querySQL 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:

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Order Of the ResultOrder 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

56

ExampleExample

SELECT sname, rating, age

FROM Sailors S

WHERE age > 50

ORDER BY rating ASC, age DESC

57

Other Relational Algebra Other Relational Algebra OperatorsOperators

• So far, we have seen selection,

projection and Cartesian product

• How do we do operators UNION and

MINUS?

58

Three SET OperatorsThree 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?

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What does this return?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 ?

Then how can we query sailors who have reserved both a green and a red boat?

60

Sailors who’ve reserved red Sailors who’ve reserved red oror green boatgreen 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?

61

Sailors who’ve reserved red Sailors who’ve reserved red andand green boatsgreen 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’;

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Multiset (Bag) OperatorsMultiset (Bag) Operators

• Union without removing duplicates:

UNION ALL

SELECT DISTINCT sname

FROM Sailors S

UNION ALL

SELECT DISTINCT sname

FROM Sailors S

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Nested QueriesNested Queries

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Nested queries in WHERENested 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?

65

Nested queries in WHERENested 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?

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What does this produce?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'))

67

Set-Comparison QueriesSet-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 >, <, =, >=, <=, or <>).

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Correlated Nested QueriesCorrelated 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

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Exists and Not ExistsExists and Not Exists

• Differs 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.