The document introduces common data types in SQL such as char, varchar, int, numeric, and date. It describes how to create databases and tables using SQL statements like CREATE DATABASE, CREATE TABLE, INSERT INTO, and ALTER TABLE. It also covers SQL queries using SELECT, FROM, WHERE, ORDER BY, LIKE and other clauses to retrieve and filter data from one or more tables.
2. Domain Types in SQL
char(n). Fixed length character string, with user-specified length n.
varchar(n). Variable length character strings, with user-specified
maximum length n.
int. Integer (a finite subset of the integers that is machine-dependent).
smallint. Small integer (a machine-dependent subset of the integer
domain type).
numeric(p,d). Fixed point number, with user-specified precision of
p digits, with n digits to the right of decimal point.
real, double precision. Floating point and double-precision floating
point numbers, with machine-dependent precision.
float(n). Floating point number, with user-specified precision of at
least n digits.
More are covered in Chapter 4.
4. Integrity Constraints in Create Table
not null
primary key (A1, ..., An )
foreign key (Am, ..., An ) references r
Example: Declare ID as the primary key for instructor
.
CREATE TABLE Persons
(
ID int NOT NULL,
LastName varchar(255) NOT NULL,
FirstName varchar(255),
PRIMARY KEY (ID)
);
primary key declaration on an attribute automatically ensures not null
5. Integrity Constraints in Create Table
CREATE TABLE Orders
(
O_Id int NOT NULL,
OrderDetails varchar(255) NOT NULL,
P_Id int,
PRIMARY KEY (O_Id),
FOREIGN KEY (P_Id) REFERENCES Persons(ID)
);
6. Insert into table
INSERT INTO table_name
VALUES (value1,value2,value3,...);
Example:
insert into instructor values (‘10211’, ’Smith’, ’Biology’,
66000);
insert into instructor values (‘10211’, null, ’Biology’, 66000);
7. Basic Query Structure
A typical SQL query has the form:
select A1, A2, ..., An
from r1, r2, ..., rm
where P
Ai represents an attribute (desired column names)
Ri represents a relation (table names)
P is a predicate (Condition)
8. The select Clause
Example: find the names of all instructors:
select name
from instructor
NOTE: SQL names are case insensitive (i.e., you may use upper- or
lower-case letters.)
E.g. Name ≡ NAME ≡ name
Some people use upper case wherever we use bold font.
9. The select Clause (Cont.)
distinct
Find the names of all departments with instructor, and remove
duplicates
select distinct dept_name
from instructor
all
The keyword all specifies that duplicates not be removed.
select all dept_name
from instructor
10. The select Clause (Cont.)
An asterisk in the select clause denotes “all attributes”
select *
from instructor
The select clause can contain arithmetic expressions involving
the operation, +, –, , and /, and operating on constants or
attributes of tuples.
The query:
select ID, name, salary/12
from instructor
would return a relation that is the same as the instructor relation,
except that the value of the attribute salary is divided by 12.
11. The where Clause
To find all instructors in Comp. Sci. dept with salary > 80000
select name
from instructor
where dept_name = ‘Comp. Sci.' and salary > 80000
Comparison results can be combined using the logical
connectives and, or, and not.
Comparisons can be applied to results of arithmetic expressions
(<=, <, >, >=, !=).
12. Where Clause Predicates
between
Example: Find the names of all instructors with salary between
$90,000 and $100,000 (that is, $90,000 and $100,000)
select name
from instructor
where salary between 90000 and 100000
select name, course_id
from instructor, teaches
where (instructor.ID, dept_name) = (teaches.ID, ’Biology’);
13. The from Clause
The from clause lists the relations involved in the query
select
from instructor, teaches
generates every possible instructor – teaches pair, with all
attributes from both relations
14. Drop and Alter Table Constructs
drop table customers
Deletes the table and its contents
>>DROP TABLE table_name
>>DROP DATABASE database_name
delete from customers
Deletes all contents of table, but retains table
DELETE FROM Customers
WHERE CustomerName='Alfreds Futterkiste' AND
ContactName='Maria Anders';
15. Drop and Alter Table Constructs
alter table
alter table- add
ALTER TABLE table_name
ADD column_name datatype
ALTER TABLE Customers
ADD Customer_Joindate Date
alter table- drop
ALTER TABLE table_name
DROP COLUMN column_name
ALTER TABLE Customers
DROP Customer_Joindate Date
16. The Rename (As) Operation
The SQL allows renaming relations and attributes using the as clause:
old-name as new-name
E.g.
select ID, name, salary/12 as monthly_salary
from instructor
Find the names of all instructors who have a higher salary than
some instructor in ‘Comp. Sci’.
select distinct T. name
from instructor as T, instructor as S
where T.salary > S.salary and S.dept_name = ‘Comp. Sci.’
17. Like- String Operations
percent (%). The % character matches any substring.
underscore (_). The _ character matches any character.
Find the names of all instructors whose name includes the substring
“dar”.
select name
from instructor
where name like '%dar%'
Match the string “100 %”
select name
from instructor
where attendance like ‘100 %' escape ''
18. Order by - Ordering the Display of
Tuples
List in alphabetic order the names of all instructors
select distinct name
from instructor
order by name
We may specify desc for descending order or asc for
ascending order, for each attribute; ascending order is the
default.
Example: order by name desc
Can sort on multiple attributes
Example: order by dept_name, name