SQL notes for learning Database, Study notes of Database Management Systems (DBMS)

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SQL

What is SQL?

• SQL stands for Structured Query Language

• SQL is a standard language for storing,

manipulating and retrieving data in databases.

• SQL lets you access and manipulate databases

• SQL is an ANSI (American National Standards

Institute) standard

• (^) SQL is a language that all commercial RDBMS

implementations understand.

• SQL is a non-procedural language
• We would be discussing SQL with respect to

oracle syntax

How SQL Works?

• (^) DDL (Data Definition Language)
  • (^) Create - Creates a new table, a view of a table, or other object in the database.
  • (^) Alter - Modifies an existing database object, such as a table.
  • (^) Drop - Deletes an entire table, a view of a table or other objects in the database.
  • (^) Truncate - Is used to delete complete data from an existing table. SQL Statements

• (^) DML (Data Manipulation Language)
  • (^) Insert - Creates a record.
  • (^) Update - Modifies records.
  • (^) Delete - Deletes records.
  • (^) Select - Retrieves certain records from one or more tables. SQL Statements

• (^) TCL (Transaction Control Language)
  • (^) Commit - To save the changes.
  • (^) Rollback - To roll back the changes. SQL Statements

Data types Data Type Explanation Char (size) Where size is the number of characters to store. Fixed length strings. Space padded. The maximum number of characters this data type can hold is 255 characters. Varchar(size)/ varchar2(size) Where size is the number of characters to store. variable length strings. Date Standard format is DD – MON – YY Number(p , s) Where p is the precision ands is the scale. For ex. Number(7,2) is a number that has 5 digits before the decimal and 2 digits after the decimal.

DDL(Data Definition Language)

Creating and Managing Tables

Database Objects

What is a table?

• The data in an RDBMS is stored in database

objects which are called as tables. This table is

basically a collection of related data entries

and it consists of numerous columns and rows.

• Remember, a table is the most common and

simplest form of data storage in a relational

database. The following program is an example

of a CUSTOMERS table −

What is a field?

• Every table is broken up into smaller entities

called fields. The fields in the CUSTOMERS

table consist of ID, NAME, AGE, ADDRESS and

SALARY.

• A field is a column in a table that is designed

to maintain specific information about every

record in the table.

What is a Record or a Row?

• A record is also called as a row of data is each

individual entry that exists in a table. For

example, there are 7 records in the above

CUSTOMERS table.

1 Ramesh 23 Ghaziabad 22,