Query : It is an operation that retrieves data from one or more tables or views.

Select statement : The SELECT statement is used to retrieve data from one or more tables, object tables, views, object views or materialized views.

Prerequisites :

• The user must have the select privileges on the specified object.
• The select any table allows to select the data from any recognized object.

Capabilities of SQL SELECT statement:


The SELECT statement can be used to select or retrieve data from the object using any one the following criteria.

SELECTION : It chooses the rows in a table that are expected to return by a query.

PROJECTION : It chooses the columns in a table that are expected to return by a query.

JOIN : It chooses the data from one or more number of tables by creating a link between them.

Basic SELECT Syntax :

SELECT [DISTINCT]{*,column [Alias],.................} From Table;

• SELECT : Identifies column
• FROM : Identifies table
• DISTINCT : suppresses duplicates
• * : Select all columns
• COLUMN : Select the named column
• ALIAS : Gives selected columns different column names
• FROM Table : Specifies the table containing the columns.

In Oracle there are 4 test tables or 4 sample tables which are useful to us. They are emp, dept, salgrade, bonus.
To know the column names and data types type below statements

DESC Emp
DESC Dept
DESC Salgrade
DESC Bonus

Retrieving Data From All Columns :

SELECT * FROM Emp;
SELECT * FROM Dept;
SELECT * FROM Salgrade;

• In this '*' is a projection operator.
• It projects data from all the columns existing in the table with all records.
• The data is displayed in a table format.

Retrieving Data From Specified Columns :

SELECT Empno, Ename, Sal FROM Emp;
SELECT Empno, Ename, Job,Dept,Sal FROM Emp;
SELECT Deptno, Dname, Loc FROM Dept;
SELECT Hisal, Losal, Grade FROM Salgrade;

• The column names need not be in the same order as table.
• The columns should be separated using comma.
• The column names can be separated onto different lines within the sql buffer.
• The casing of column names is not important.

Column Heading Defaults :

• The default justification of the data after it is retrieved from the table is

LEFT : Date and Character Data
RIGHT : Numeric Data

• The default display of the data is always is upper casing.
• The character and date column hedings can be truncated, but numbers cannot be truncated.