1. UNIT – III
Form of basic SQL Query
Examples of Basic SQL Queries
Introduction to Nested Queries
Correlated Nested Queries set
Comparison operators
Aggregative operators
NULL values – comparison using NULL values
Logical connectivity’s – AND, OR and NOT
Impact on SQL constructs
Outer joins
Disallowing NULL values
Complex Integrity Constraints in SQL Triggers
Active Data base.

2. Structured Query Language
(SQL)

3. SELECT [DISTINCT ] select-list
A query is a statement requesting the retrieval of information
The portion of a DML that involves information retrieval is called a query language
SQL is the most widely used commercial relational database language
THE FORM OF A BASIC SQL QUERY
SELECT [DISTINCT ] select-list
FROM from-list
WHERE qualification
SELECT clause specifies columns to be retained in the result
FROM clause specifies a cross-product of tables

4. Optional WHERE clause specifies selection conditions on the tables mentioned in the FROM clause
Example
Attribute (or) Field
Record (or)
Tuple
Fig 4.1 Sailors table

5. FROM Sailors Question: Find the names and ages of all sailors
Query: SELECT DISTINCT sname, age
FROM Sailors
Output:
Note: The DISTINCT keyword can be used to return only distinct (different) values

6. FROM Sailors Question: Find the names and ages of all sailors
Query: SELECT sname, age
FROM Sailors
Output:

7. FROM Sailors WHERE rating >7 SELECT * FROM Sailors
Question: Find all sailors with a rating above 7
Query: SELECT sid, sname, rating, age
FROM Sailors
WHERE rating >7
(or)
SELECT *
FROM Sailors
WHERE rating>7
Output:

8. The SQL language has Three parts -Data Definition Language (DDL)
-Data Manipulation Language (DML)
-Data Control Language(DCL)
Data Definition Language (DDL):
DDL supports the creation, deletion, and modification of definitions for tables and views
Integrity constraints can be defined on tables, either when the table is created or later
The DDL also provides commands for specifying access rights or privileges to tables and views
It also provide commands for creating and deleting indexes

9. Data Manipulation Language (DML):
DML allows users to pose queries and to insert, delete, and modify rows
Data Control Language (DCL):
DCL controls a database, including administrative privileges and saving data

10. Specifies the kind of data that a field stores
Data type
Specifies the kind of data that a field stores
Character data types
VARCHAR2
Stores variable-length character data up to a maximum of 4,000 characters
Values in different records can have a different number of characters
VARCHAR
Same as VARCHAR2, but it is in ANSI standard
Syntax: Fieldname VARCHAR2(maximum-size)

11. Fixed-length character data up to a maximum size of 2,000 characters
Data values for different records all have the same number of characters
DBMS adds trailing blank spaces to the end of the entry to make the entry fill the maximum size value
Data longer than maximum size causes an error
Syntax: Fieldname CHAR[(maximum-size)]
NVARCHAR2 and NCHAR
Analogous to VARCHAR2 and CHAR but use Unicode rather than ASCII
Used to hold character data in languages other then English

12. Variable-Length character data up to 2 GB, max. of one per table
LONG
Variable-Length character data up to 2 GB, max. of one per table
Number data types
Stores negative, positive, fixed and floating point numbers with precision up to 38 decimal places
Syntax: Fieldname NUMBER[(precision , scale)]
Integer: Fieldname NUMBER (precision)
Fixed Point: Fieldname NUMBER[(precision , scale)]
Date and Time data types
Date
Dates from December 31,4712 BC to December 31,4712 AD
Default format DD-MON-YY
Default time format HH:MI:SS AM

13. Similar to DATE but stores fractional seconds
Syntax: Fieldname DATE
Timestamp
Similar to DATE but stores fractional seconds
Syntax: Fieldname TIMESTAMP(Fractional-seconds-pre)
DDL Commands
-CREATE
-ALTER
-DROP
-GRANT
-REVOKE
-TRUNCATE

14. Used to add attributes to an existing relation(table)
CREATE command
Used to create table
Syntax:
CREATE TABLE table-name (Fieldname1 data_type , Fieldname2 data_type , …. ….. ….)
Example
CREATE TABLE Sailors ( sid NUMBER(2), sname VARCHAR2(20), rating NUMBER(2))
ALTER command
Used to add attributes to an existing relation(table)
All rows in the relation(table) are assigned ‘null’ as the value for the new attributes
Syntax: ALTER TABLE tablename
ADD (fieldname Field_datatype)

15. MODIFY (fieldname new_field_datatype)
Example: ALTER TABLE Sailors
ADD (age NUMBER(2))
Modifying an existing field
Syntax: ALTER TABLE tablename
MODIFY (fieldname new_field_datatype)
Example
ALTER TABLE Sailors MODIFY (age NUMBER(3,1))
Deleting an existing field
DROP COLUMN Fieldname
Example: ALTER TABLE Sailors DROP COLUMN age
DROP command
Used to delete an existing table
Syntax: DROP TABLE tablename
Example: DROP TABLE Sailors

16. INSERT INTO Sailors values (22,’Dustin’,7,45.0)
DML Commands
-INSERT
-DELETE
-UPDATE
-SELECT
INSERT command
Inserting record into a table
Syntax: INSERT INTO table-name VALUES (field1,field2,…)
Example:
INSERT INTO Sailors values (22,’Dustin’,7,45.0)
Inserting a record that has some null attributes
Requires identifying the fields that actually get data
Syntax: INSERT INTO table-name (field1,field4) VALUES (value1,value2)

17. Inserting records from another table
Syntax: INSERT INTO table_name1 SELECT * FROM table_name2
UPDATE command
For modifying attribute values of (some) tuples in a table
Syntax: UPDATE tablename SET column1=value1,…, columnn=valuen WHERE condition
Example: UPDATE Sailors SET age=34.5 WHERE sid=22
DELETE command
Removing specified rows from a table
Syntax: DELETE FROM tablename WHERE condition
Example: DELETE FROM Sailors WHERE sid=22

18. (or) Removing all rows from a table Syntax: DELETE FROM tablename
Example: DELETE FROM Sailors
(or)
Syntax: TRUNCATE table Sailors
Example: TRUNCATE table Sailors
Note: TRUNCATE Removes all rows from a table without backup
Fig 4.2 Boats table

19. Fig 4.3 Reserves table

20. Used to define range limits SNAME Dustin Lubber Horatio
AND, OR and NOT Operators
Question: Find the names of sailors who have reserved boat number 103
Query: SELECT sname FROM Sailors S, Reserves R WHERE S.sid=R.sid AND R.bid=103
Output:
BETWEEN
Used to define range limits
Question: Find all sailors whose age is in between 45.0 and 63.5
Query: SELECT * FROM Sailors S WHERE S.age BETWEEN 45.0 AND 63.5
SNAME
Dustin
Lubber
Horatio

21. SID SNAME RATING AGE SID SNAME RATING AGE
Output: IN
Used to check whether an attribute value matches a value contained within a set of listed values
Question: Find all sailors whose age is in the list of values(15.0,33.2,45.7,63.5)
Query: SELECT * FROM Sailors S WHERE S.age IN (15.0,33.2,45.7,63.5)
SID
SNAME
RATING
AGE 22
Dustin 7 45 31
Lubber 8
55.5 95
Bob 3
63.5
SID
SNAME
RATING
AGE 95
Bob 3
63.5

22. SID SNAME RATING AGE SID SNAME RATING AGE
STRING operators
“%” character is used to match any substring
“_” character is used to match any character
Expresses patterns by using the ‘like’ comparison operator
Example1
SELECT * FROM Sailors WHERE sname LIKE '_u%'
Output:
Example2
SELECT * FROM Sailors WHERE sname LIKE 'A_d_'
SID
SNAME
RATING
AGE 22
Dustin 7 45 31
Lubber 8
55.5 58
Rusty 10 35
SID
SNAME
RATING
AGE 32
Andy 8
25.5

23. <query 1> <set operator> <query 2>
SET operators
Operations such as union, intersect, minus and exists operate on relations
Corresponding to relational-algebra operations U, ∩ and –
Relations participating in the operations must be compatible; i.e., must have same set of attributes
<query 1> <set operator> <query 2>
union returns a table consisting of all rows either appearing in the result of <query1> or in the result of <query 2>
intersect returns all rows that appear in both results <query 1> and <query 2>
minus returns those rows that appear in the result of <query 1> but not in the result of <query 2>

24. SELECT * FROM Sailors UNION SELECT * FROM Sailors1 Example (union)
Output:

25. SELECT * FROM Sailors INTERSECT SELECT * FROM Sailors1
Example (intersect)
SELECT * FROM Sailors
INTERSECT
SELECT * FROM Sailors1
Output:

26. A nested query is a query that has another query embedded within it
Example (minus)
SELECT * FROM Sailors
MINUS
SELECT * FROM Sailors1
Output: no rows selected
Nested Queries
A nested query is a query that has another query embedded within it
The embedded query is called a subquery
A subquery typically appears within the WHERE clause of a query
Subqueries can sometimes appear in the FROM clause or the HAVING clause

27. SNAME Dustin Lubber Horatio Introduction to Nested Queries
Question: Find the names of sailors who have reserved boat 103
Query: SELECT S.sname FROM Sailors S WHERE S.sid IN (SELECT R.sid FROM Reserves R WHERE R.bid=103)
Output:
Question: Find the names of sailors who have reserved a blue boat
Query: SELECT S.sname FROM Sailors S WHERE S.sid IN (SELECT R.sid FROM Reserves R WHERE R.bid IN (SELECT B.bid FROM Boats B WHERE B.color='blue'))
SNAME
Dustin
Lubber
Horatio

28. Output:
Correlated Nested Queries
In the nested queries, the inner subquery has been completely independent of the outer query
In general the inner subquery could depend on the row that is currently being examined in the outer query
Question: Find the names of sailors who have reserved boat 103
Query: SELECT S.sname FROM Sailors S WHERE EXISTS ( SELECT * FROM Reserves R WHERE R.bid = 103 AND R.sid = S.sid )
SNAME
Dustin
Horatio

29. The EXISTS operator is another set comparison operator, such as IN
SNAME
Dustin
Lubber
Horatio
Output:
The EXISTS operator is another set comparison operator, such as IN
It allows us to test whether a set is nonempty. Thus, for each Sailor row S, we test whether the set of Reserves rows R such that R.bid = 103 AND S.sid = R.sid is nonempty. If so, sailor S has reserved boat 103, and we retrieve the name
The subquery clearly depends on the current row S and must be re-evaluated for each row in Sailors
The occurrence of S in the subquery (in the form of the literal S.sid) is called a correlation, and such queries are called correlated queries.

30. Greater than or equal to
COMPARISION OPERATORS
The following operators can be used in ‘WHERE’ clause
Example
Question: Find sailors whose rating is better than some sailor called Horatio
Query: SELECT S1.sname, S1.rating FROM Sailors S1 WHERE S1.rating > ANY ( SELECT S2.rating FROM
SYMBOL
MEANING =
Equal to
<
Less than
<=
Less than or equal to
>
Grater than
>=
Greater than or equal to
<> or != or ^=
Not equal to

31. Sailors S2 WHERE S2.sname='Horatio' )
Output:
If there are several sailors called Horatio, this query finds all sailors whose rating is better than that of some sailor called Horatio
Question: Find sailors whose rating is better than some sailor called Horatio
Query: SELECT S1.sname, S1.rating FROM Sailors S1 WHERE S1.rating > ALL ( SELECT S2.rating FROM
SNAME
RATING
Rusty 10
Zorba
Horatio 9
Lubber 8
Andy

32. Sailors S2 WHERE S2.sname='Horatio' )
Output:
AGGREGATE OPERATORS
In addition to simply retrieving data, we often want to perform some computation or summarization
SQL supports the following aggregate operations, which can be applied on any column, say A, of a relation(table):
1. COUNT ([DISTINCT] A): The number of (unique) values in the A column
2. SUM ([DISTINCT] A): The sum of all (unique) values in the A column
3. AVG ([DISTINCT] A): The average of all (unique) values in the A column
SNAME
RATING
Rusty 10
Zorba

33. 4. MAX (A): The maximum value in the A column
5. MIN (A): The minimum value in the A column
Note: not specify DISTINCT in conjunction with MIN or MAX
Examples:
Question: Find the average age of all sailors
Query: SELECT AVG (age) FROM Sailors
Output:
Question: Find the name and age of the oldest sailor
Query: SELECT S1.sname, S1.age FROM Sailors S1 WHERE S1.age = ( SELECT MAX (S2.age) FROM Sailors S2 )
AVG(AGE)
36.9
SNAME
AGE
Bob
63.5

34. SELECT [ DISTINCT ] select-list FROM from-list WHERE qualification
Question: Count the number of sailors
Query: SELECT COUNT (*) FROM Sailors
Output:
The GROUP BY and HAVING Clauses
We have applied aggregate operations to all (qualifying) rows in a relation(table)
GROUP BY used to apply aggregate operations to each of a number of groups of rows in a relation
HAVING is used to place a condition, which is applied on the groups of rows
general form:
SELECT [ DISTINCT ] select-list
FROM from-list
WHERE qualification
GROUP BY grouping-list HAVING group-qualification
COUNT(*) 10

35. RATING COUNT(RATING) 1 3 2 7 8 9 10 Examples
Question: Find the number of sailors belongs to each rating level
Query: SELECT rating, COUNT(rating) FROM Sailors GROUP BY rating
Output:
RATING
COUNT(RATING) 1 3 2 7 8 9 10

36. Question: Find the age of the youngest sailor for each rating level
Query: SELECT rating, MIN (age) FROM Sailors GROUP BY rating
Output:
RATING
MIN(AGE) 1 33 3
25.5 7 35 8 9 10 16

37. Question: Find the age of the youngest sailor for each rating level, which is greater than 7
Query: SELECT rating, MIN (age) FROM Sailors GROUP BY rating HAVING rating>7
Output:
ORDER BY
The order by clause is used to sort the tuples in a query result based on the values of some attributes
Example
Question: display the sailors table in the ascending order of sname
RATING
MIN(AGE) 8
25.5 9 35 10 16

38. SID SNAME RATING AGE 32 Andy 8 25.5 85 Art 3 95 Bob 63.5 29 Brutus 1
Query: SELECT * FROM Sailors ORDER BY sname
Output:
SID
SNAME
RATING
AGE 32
Andy 8
25.5 85
Art 3 95
Bob
63.5 29
Brutus 1 33 22
Dustin 7 45 64
Horatio 35 74 9 31
Lubber
55.5 58
Rusty 10 71
Zorba 16

39. SID SNAME RATING AGE 71 Zorba 10 16 58 Rusty 35 31 Lubber 8 55.5 64
Question: display the sailors table in the descending order of sname
Query: SELECT * FROM Sailors ORDER BY sname DESC
Output:
SID
SNAME
RATING
AGE 71
Zorba 10 16 58
Rusty 35 31
Lubber 8
55.5 64
Horatio 7 74 9 22
Dustin 45 29
Brutus 1 33 95
Bob 3
63.5 85
Art
25.5 32
Andy

40. We use null when the column value is either unknown
NULL VALUES
Thus far, we have assumed that column values in a row are always known. In practice column values can be unknown
We use null when the column value is either unknown
Example
Insert the row (98,Dan,null,39) to represent Dan into sailors table
Query: INSERT INTO Sailors VALUES(98,'Dan',null,39)
Query: SELECT * FROM Sailors

41. SID SNAME RATING AGE 22 Dustin 7 45 29 Brutus 1 33 31 Lubber 8 55.5 32
Output:
SID
SNAME
RATING
AGE 22
Dustin 7 45 29
Brutus 1 33 31
Lubber 8
55.5 32
Andy
25.5 58
Rusty 10 35 64
Horatio 71
Zorba 16 74 9 85
Art 3 95
Bob
63.5 98
Dan 39

42. Consider a comparison such as rating = 8
Comparisons Using Null Values
Consider a comparison such as rating = 8
If this is applied to the row for Dan, is this condition true or false? Since Dan's rating is unknown, it is reasonable to say that this comparison should evaluate to the value unknown
This is the case for the comparisons rating > 8 and rating < 8 as well
SQL also provides a special comparison operator IS NULL to test whether a column value is null
for example, we can say rating IS NULL, which would evaluate to true on the row representing Dan
We can also say rating IS NOT NULL, which would evaluate to false on the row for Dan
Example
Query: SELECT * FROM sailors WHERE rating IS NULL

43. what about boolean expressions such as rating = 8 OR age < 40
Output:
Logical Connectives AND, OR, and NOT
what about boolean expressions such as
rating = 8 OR age < 40
rating = 8 AND age < 40?
Considering the row for Dan again, because age < 40, the first expression evaluates to true regardless of the value of rating, but what about the second? We can only say unknown
The expression NOT unknown is defined to be unknown
SID
SNAME
RATING
AGE 98
Dan 39

44. OR of two arguments evaluates to true if either argument evaluates to true, and to unknown if one argument evaluates to false and the other evaluates to unknown
AND of two arguments evaluates to false if either argument evaluates to false, and to unknown if one argument evaluates to unknown and the other evaluates to true or unknown
Impact on SQL Constructs
In the presence of null values, any row that evaluates to false or to unknown is eliminated
Eliminating rows that evaluate to unknown has a subtle but significant impact on queries, especially nested queries involving EXISTS or UNIQUE
If we compare two null values using =, the result is unknown! In the context of duplicates, this comparison is implicitly treated as true, which is an anomaly

45. The arithmetic operations +, - ,
The arithmetic operations +, - ,* , / and = all return null if one of their arguments is null
nulls can cause some unexpected behavior with aggregate operations
COUNT(*) handles null values just like other values, that is, they get counted
All the other aggregate operations (COUNT, SUM, AVG, MIN, MAX, and variations using DISTINCT) simply discard null values

46. join operation that rely on null values, called outer joins
Consider the join of two tables, say Sailors Reserves
In a full outer join, ‘matching rows’ plus ‘Sailors rows without a matching Reserves rows’ (columns inherited from Reserves assigned null values) plus ‘Reserves rows without a matching Sailors rows’ (columns inherited from Sailors assigned null values) appear in the result
In a left outer join, ‘matching rows’ plus ‘Sailors rows without a matching Reserves rows’ (columns inherited from Reserves assigned null values) appear in the result

47. LEFT OUTER JOIN Reserves R ON S.sid=R.sid
In a right outer join, ‘matching rows’ plus ‘Reserves rows without a matching Sailors rows’ (columns inherited from Sailors assigned null values) appear in the result
Note: In inner join only matching rows appear in the result
Example
Query: SELECT S.sid,S.sname, R.bid,R.day FROM Sailors S
LEFT OUTER JOIN Reserves R
ON S.sid=R.sid
Disallowing Null Values
We can disallow null values by specifying NOT NULL as part of the field definition, for example, sname CHAR(20) NOT NULL
The fields in a primary key are not allowed to take on null values
There is an implicit NOT NULL constraint for every field listed in a PRIMARY KEY constraint

48. CHECK conditional-expression
COMPLEX INTEGRITY CONSTRAINTS IN SQL
Constraints over a Single Table
We can specify complex constraints over a single table using table constraints, which have the form
CHECK conditional-expression
For example, to ensure that rating must be an integer in the range 1 to 10, we could use:
CREATE TABLE Sailors ( sid INTEGER, sname CHAR(10),rating INTEGER,age REAL,
PRIMARY KEY (sid),
CHECK ( rating >= 1 AND rating <= 10 ))
To enforce the constraint that Interlake boats cannot be reserved, we could use:
CREATE TABLE Reserves ( sid INTEGER,bid INTEGER,
day DATE,
FOREIGN KEY (sid) REFERENCES Sailors

49. FOREIGN KEY (bid) REFERENCES Boats CONSTRAINT noInterlakeRes
CHECK ( `Interlake' <>
( SELECT B.bname FROM Boats B WHERE B.bid = Reserves.bid )))
When a row is inserted into Reserves or an existing row is modied, the conditional expression in the CHECK constraint is evaluated. If it evaluates to false, the command is rejected
Domain Constraints
A user can dene a new domain using the CREATE DOMAIN statement, which makes use of CHECK constraints
CREATE DOMAIN ratingval INTEGER DEFAULT 0
CHECK ( VALUE >= 1 AND VALUE <= 10 )

50. Assertions, which are constraints not associated with any one table
INTEGER is the base type for the domain ratingval, and every ratingval value must be of this type. Values in ratingval are further restricted by using a CHECK constraint
Once a domain is defined, the name of the domain can be used to restrict column values in a table
rating ratingval
Assertions: ICs over Several Tables
Table constraints are associated with a single table, although the conditional expression in the CHECK clause can refer to other tables
Table constraints are required to hold only if the associated table is nonempty
Assertions, which are constraints not associated with any one table

51. As an example, suppose that we wish to enforce the constraint that the number of boats plus the number of sailors should be less than 100. (This condition might be required, say, to qualify as a `small' sailing club.) We could try the following table constraint:
CREATE TABLE Sailors ( sid INTEGER, sname CHAR(10),rating INTEGER,age REAL,PRIMARY KEY (sid),
CHECK ( rating >= 1 AND rating <= 10)
CHECK ( ( SELECT COUNT (S.sid) FROM Sailors S )
+ ( SELECT COUNT (B.bid) FROM Boats B )
< 100 ))
CREATE ASSERTION smallClub
+ ( SELECT COUNT (B.bid) FROM Boats B) < 100 )

52. A trigger description contains three parts:
TRIGGERS AND ACTIVE DATABASES
A trigger is a procedure that is automatically invoked by the DBMS in response to specified changes to the database, and is typically specified by the DBA
A database that has a set of associated triggers is called an active database
A trigger description contains three parts:
Event: A change to the database that activates the trigger
Condition: A query or test that is run when the trigger is activated
Action: A procedure that is executed when the trigger is activated and its condition is true
Examples of Triggers in SQL
CREATE TRIGGER init count BEFORE INSERT ON Students /* Event */
DECLARE count INTEGER;

53. BEGIN /* Action */
count := 0;
END
CREATE TRIGGER incr count AFTER INSERT ON Students /* Event */
WHEN (new.age < 18) /* Condition; `new' is just-inserted tuple */
FOR EACH ROW
BEGIN /* Action */
count := count + 1;

54. Assignment - 3
1. (a) Consider the following schema given. The primary keys are underlined.
Sailors(sailor-id, sailor-name, sailor-rating, sailor-age)
Boats(boat-id, boat-name, boat-color)
Reserves(sailor-id, boat-id, day)
Write the Nested queries in SQL.
i. Find the names of sailors who have reserved boat number 120
ii. Find the names of sailors who have reserved a green boat
iii. Find the names of sailors who have not reserved a green boat
iv. Find the names of sailors with the highest rating
(b) Explain the GROUP BY and HAVING clauses.
(a) Consider the following scheme for the COMPANY database. The
primary keys are underlined.
Employee (SSN, Fname, Lname, Birthdate, Address, Salary, Dnumber)
Department (Dnumber, Dname, Dlocation)
Perform the following operations using SQL. Assume the data:
i. Insert a record into employee table
ii. Delete an employee with SSN equal to 10.
iii. Update the Dnumber of the employee tuple having salary greater than Rs 10,000.
iv. Retrieve the name and address of all employees who work for the ”XYZ” department.

55. 3 (a) Explain with an example in SQL
i. Unspecified where-clause and use of Asterisk
ii. Exist and not exists
iii. Explicit sets and NULLS
iv. Renaming attributes and joined tables.
(b) Why are null values not preferred in a relation?
4 (a) Explain the general syntax of SELECT command
(b) What are the steps followed while creating a table in SQL?
(a) What are the various salient features of the SQL?
(b) Write short notes on:
i) Key constraints
ii) General constraints
6 (a) What is the role of SQL in a database architecture?
(b) What are the notations used in SQL commands?
7 (a) Explain the various types of aggregate functions with suitable
examples in SQL
(b) Explain the following
(i) Key constraints
(ii) Foreign key constraints
(iii) General constraints

56. 8 a) Consider the following schema:
Suppliers(sid, sname, saddress)
Parts(pid, pname, color)
Catalog(sid, pid, cost)
The key fields are underlined. Write the following queries in relational algebra
(i) Find the names of suppliers who supply blue part
(ii) Find the sids of suppliers who supply every red part
(iii) Find the pids of parts that are supplied by at least two different suppliers
(iv) Find all the pids of parts supplied by supplier with sid=200
(v) Find the pids of parts supplied by every supplier at less than Rs 500
9 Distinguish between DDL and DML
10 Explain various integrity constraints.