SQL Sangeeta Devadiga CS157A, Fall 2006

Outline Background Data Definition Basic Structure Set Operation

Background IBM developed the original version named sequel in early 1970’s Sequel language has evolved into SQL SQL (Structured Query Language) Versions of SQL SQL 92 SQL 99 SQL 2003 (latest version)

Parts of SQL Data Definition Language (DDL) Data manipulation Language (DML) Integrity View Definition Transaction control Embedded SQL and Dynamic SQL Authorization

Basic Domain Types char(n): A fixed length character string with user specifed length n. character can be used instead. varchar(n): A variable length character string with user specified max length n. character varying is equivalent. int: An Integer, the full form integer is equivalent. smallint: A small integer, a subset of integer domain type numeric(p,d): A fixed point number with user specified precision. E.g: numeric(3,1) allows 31.5 to be defined precisely real, double precision: Floating-point and double precision floating-point numbers with machine-dependent precision. float(n): A floating point number, with precision of at least n digits.

Basic Schema Definition in SQL We create SQL relation using the create table command create table r( A 1 D 1, A 2 D 2, ….., A n D n, (integrity constraint 1 ), ………., (integrity constraint k )) r  is the name of relation A 1 ….A n  are the names of attributes D 1 …D n  are the types of values in the domain

Examples create table Example 1: create table customer (customer_name char(20), customer_street char(30), customer_city char(30), primary key (customer_name))

Example 2 create table account (account_number char(10), branch_name char(15), balance numeric (12, 2), primary key (account_number))

Basic SQL Query Structure SQL is based on set and relational operations with some modification and enhancement. SQL query has the form select A 1,A 2, …,A n from r 1, r 2, ….,r m where P A1 is a attribute r1 represents a relation P is a predicate Equivalent Query:  A 1, A 2, …, A n (  P (r 1 X r 2 X …… X r m )) The result of a SQL query is a relation

Example select Clause select branch_name from loan In relational Algebra, the query would be  branch_name (loan) SQL allows duplicates in query result use distinct if no duplicates in result use all if duplicates required in result select distinct branch_name from loan (result has distinct branch names) select all branch_name from loan (result may have duplicates)

Where Clause Corresponds to the selection predicate of relational algebra To find loan numbers for loans made at San Jose branch with loan amounts greater than $500 select loan_number from loan where branch_name = “San Jose” and amount > $500 Comparison result can be combined with logical connectives and, or, and not SQL includes between comparison operator To find loan numbers between amt. 900 and 10,000 select loan_number from loan where amount between 900 and 10000

From Clause Corresponds to Cartesian product operation of relational algebra Example: To find name, loan number, amount of all customers having loan at San Jose branch. select customer_name, loan_number, amount from borrower, loan where borrower.loan_number = loan.loan_number and branch_name = “San Jose”

Rename SQL allows renaming relations and attributes using as clause Example: To find name, loan_number, amount of all customers and rename column loan_number as loan_id. select customer_name, loan_number as loan_id, amount from borrower, loan where borrower.loan_number = loan. loan_number

Set Operation The set operations union, intersect and except corresponds to U, , - respectively of relational algebra. Each of the above operation automatically eliminates duplicates To retain all duplicates use union all, intersect all, except all

Examples Set Operations Find all customers who have a loan, a account or both: select customer_name from depositor union select customer_name from borrower Find all customers who have both loan and an account: select customer_name from depositor intersect select customer_name from borrower Find all customers who have an account, but no loan: select customer_name from depositor except select customer_name from borrower