RDBMS
- 1. Relational Database Management System Nadar Saraswathi College of Arts & Science Submitted by N. Nagapandiyammal M. Sc (CS)
- 2. Content • Basic Structure • Set Operations • Complex Queries • Joined Relations • Data-Definition Language(DDL)
- 3. Basic Structure SQL is based on set and relational operations with certain modifications and enhancements A typical SQL query has the form select A1,A2, ..., An From r1,r2, ..., rm Where P A is represent attributes r is represent relations P is a predicate This query is equivalent to the relational algebra expression: ΠA1,A2, ..., An(P(r1 x r2 x...x rm)) The result of an SQL query is a relation.
- 4. Set Operations The set operations union, intersect, and except operate on relations and correspond to the relational algebra operations [,, and −. Each of the above operations automatically eliminates duplicates; to retain all duplicates use the corresponding multiset versions union all, intersect all and except all. Suppose a tuple occurs m times in r and n times in s, then, it occurs: m + n times in r union all s min(m, n) times in r intersect all s max(0,m−n) times in r except all s
- 5. Find all customers who have a loan, an account, or both: (Select customer-name from depositor) union (select customer-name from borrower) Find all customers who have both a 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)
- 6. Complex Queries • Complex queries are often hard or impossible to write as a single SQL block or a union / intersection / difference of SQL blocks. • Following are some very important Complex SQL Queries Examples with answers. I have tried to explain each and every query in detail so that everyone will get idea of how it is executed step-by-step. Following are some Complex SQL Queries Examples with answers in detail.
- 7. 1.Query to find Second Highest Salary of Employee? Answer: Select distinct Salary from Employee e1 where 2=Select count(distinct Salary) from Employee e2 where e1.salary<=e2.salary; 2.Query to find duplicate rows in table? Answer: Select * from Employee a where rowid <>( select max(rowid) from Employee b where a.Employee_num=b.Employee_num);
- 8. Joined Relations o Join operations take two relations and return as a result another relation. o These additional operations are typically used as sub query expressions in the from clause. o Join condition – defines which tuple in the two relations match, and what attributes are present in the result of the join. o Join type – defines how tuple in each relation that do not match any tuple in the other relation (based on the join condition) are treated. Join Types inner join left outer join right outer join full outer join Join Conditions natural on <predicate> using (A1, A2, . . ., An)
- 9. Joined Relations – Datasets for Examples Relation loan Relation borrower branch-name loan-number amount Downtown L-170 3000 Redwood L-230 4000 Perry ridge L-260 1700 customer-name loan-number Jones L-170 Smith L-230 Hayes L-260
- 10. Joined Relations – Examples loan inner join borrower on loan. loan-number =borrower. loan-number loan left outer join borrower on loan. loan-number=borrower. loan-number loan natural inner join borrower loan natural right outer join borrower loan full outer join borrower using (loan-number) Find all customers who have either an account or a loan (but not both) at the bank. select customer-name from (depositor natural full outer join borrower) where account-number is null or loan-number is null
- 11. Data Definition Language (DDL) Allows the specification of not only a set of relations but also information about each relation, including: The schema for each relation. The domain of values associated with each attribute. Integrity constraints. The set of indices to be maintained for each relation. Security and authorization information for each relation. The physical storage structure of each relation on disk.
- 12. 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.
- 13. Domain Types in SQL (Cont.) • 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. • date. Dates, containing a (4 digit) year, month and date. • time. Time of day, in hours, minutes and seconds. – Null values are allowed in all the domain types. Declaring an attribute to be not null prohibits null values for that attribute. – create domain construct in SQL-92 creates user-defined domain types create domain person-name char(20) not null
- 14. Create Table Construct • An SQL relation is defined using the create table command: create table r (A1 D1, A2 D2, . . . , An Dn, <integrity-constraint l >, . . ., <integrity-constraint>) – r is the name of the relation – each Ai is an attribute name in the schema of relation r – Di is the data type of values in the domain of attribute Ai
- 15. Integrity Constraints In Create Table not null primary key (A1, . . ., An) check (P), where P is a predicate Example: Declare branch-name as the primary key for branch and ensure that the values of assets are non-negative. create table branch (branch-name char(15) not null, branch-city char(30), assets integer, primary key (branch-name), check (assets >= 0)) primary key declaration on an attribute automatically ensures not null in SQL-92
- 16. Drop and Alter Table Constructs The drop table command deletes all information about the dropped relation from the database. The alter table command is used to add attributes to an existing relation. All tuples in the relation are assigned null as the value for the new attribute. The form of the alter table command is alter table r add A D where A is the name of the attribute be added to relation r and D is the domain of A. The alter table command can also be used to drop attributes of a relation alter table r drop A where A is the name of an attribute of relation r.
- 17. The End