CBSE Book Class 12 Informatic Practices Databases and SQL

MORE ON DATABASES AND SQL

Learning Objectives

After studying this lesson the students will be able to:

  Define the terms:

     (i) Group (Aggregate) functions, Constraints

     (ii) Cartesian Product, Join, Referential Integrity, Foreign Key.

  Write queries using aggregate functions and GROUP BY clause.

  Access data from multiple tables

  Create tables with PRIMARY KEY and NOT NULL constraints

  Add a constraint to a table, remove a constraint from a table, modify a   column of a table using ALTER TABLE command.   Delete a table using DROP TABLE.In the previous class, you have learnt some database concepts and SQL commands. You have also learnt how to create databases and tables within databases and howto access data from a table using various clauses of SELECT command. In this chapter you shall learn some more clauses and functions in SQL to access data from a table and how to access data from multiple tables of a database. It was Iftar party in Lucknow that Mr. David met Mr. Naqvi. They became friends and exchanged their phone numbers. After a few days, Mr. David rang up and invited Mr. Naqvi for New Year party at his house and gave him his house number as follows: "I live in a long street. Numbered on the side of my house are the houses one, two, three and so on. All the numbers on one side of my house add up to exactly the same as all the numbers on the other side of my house. I know there are more than thirty houses on that side of the street, but not so many as 50." With this information, Mr. Naqvi was able to find Mr. David's house number. Can you also find?

Such situations are faced by the developers of RDBMS software where they have to think of retrieval of data from multiple tables satisfying some specified conditions. Let us now move ahead with SQL and more database concepts.

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