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SQL Expressions

An expression is a combination of one or more values, operators and SQL functions that evaluate to a value. These SQL EXPRESSIONs are like formulae and they are written in query language. You can also use them to query the database for a specific set of data.

Syntax

Consider the basic syntax of the SELECT statement as follows −

SELECT column1, column2, columnN
FROM table_name
WHERE [CONDITION|EXPRESSION];

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

Boolean
Numeric
Date

Let us now discuss each of these in detail.

Boolean Expressions

SQL Boolean Expressions fetch the data based on matching a single value. Following is the syntax −

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

Consider the EMPLOYEES table having the following records −

SQL> SELECT * FROM EMPLOYEES;

ID	NAME	AGE	ADDRESS	SALARY
1	Ravi	30	Delhi	18000
2	Pawan	26	Pune	20000
3	Jignesh	28	Surat	22000
4	Vikram	25	Mumbai	25000
5	Shilpa	24	Kolkata	12000
6	Hardik	28	Chennai	20000

7 rows in set (0.00 sec)

The following table is a simple example showing the usage of various SQL Boolean Expressions −

SQL> SELECT * FROM EMPLOYEES WHERE SALARY = 20000;

ID	NAME	AGE	ADDRESS	SALARY
6	Hardik	28	Chennai	20000

1 row in set (0.00 sec)

Numeric Expression

These expressions are used to perform any mathematical operation in any query. Following is the syntax −

SELECT numerical_expression as OPERATION_NAME
[FROM table_name
WHERE CONDITION] ;

Here, the numerical_expression is used for a mathematical expression or any formula. Following is a simple example showing the usage of SQL Numeric Expressions −

SQL> SELECT (15 + 6) AS ADDITION

ADDITION
21

1 row in set (0.00 sec)

There are several built-in functions like avg(), sum(), count(), etc., to perform what is known as the aggregate data calculations against a table or a specific table column.

SQL> SELECT COUNT(*) AS "RECORDS" FROM EMPLOYEES;