SQL Expressions in DBMS

There are three different types of SQL expressions, which are mentioned below

• Boolean
• Numeric
• Date

Consider the following sample table emp

Boolean Expressions

• Boolean expressions generally correspond to a condition specified in the where clause for retrieving the required set of data
• Whenever the data you specified in the expression is matched with the data in the table then the expression evaluates to true and the record is obtained

Syntax

SELECT column1, column2, columnN 
FROM table_name 
WHERE SINGLE VALUE MATCHING EXPRESSION;

Example

select empno,ename,job,deptno,sal
from emp
where deptno=20;

O/P

4 rows selected

The above query displays the rows  of the table only if there is a match for the department number as specified in where clause i.e only when dept-no is 20.

Numeric expression

These expressions are  used to perform arithmetical calculations on the data present in the table

Syntax

SELECT numerical_expression as OPERATION_NAME
[FROM table_name
WHERE CONDITION] ;

Example

select ename,job,sal,sal*12 as annualsalary ,sal/4 as bonus from emp;

O/P

7 rows selected.

The above query perform multiplication and division operation on the data of the salary column and displayed.

Date expression

• Date expression performs manipulation on ‘date data type ‘values
• It is also used to return the current system, date timestamp and arithmetic operations on date values

Example

SELECT CURRENT_TIMESTAMP,sysdate from dual;

O/P

Example

We can also perform arithmetic operations on date values

select ename,job,sal,hiredate,hiredate+2 from emp;

O/P

7 rows selected.

Hiredate+2 is nothing but 2 days from current date value is advanced suppose it hiredate  is july 24 then hiredate +2 will give July 26