SQL Expressions

SQL Expressions Overview

An  expression is a combination of one or more values, operators, and SQL functions that evaluate to a value.

SQL EXPRESSIONs are like formulas and they are written in query language. You can also use them to query the database for 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:

 

SQL - Boolean Expressions

SQL Boolean Expressions fetch the data on the basis of matching single value. Following is the syntax:

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

Consider CUSTOMERS table has following records:

SQL> SELECT * FROM CUSTOMERS;

+----+----------+-----+-----------+----------+

| ID | NAME     | AGE | ADDRESS    | SALARY   |

+----+----------+-----+-----------+----------+

|  1 | Ramesh   |  32 | Ahmedabad |  2000.00 |

|  2 | Khilan   |  25 | Delhi     |  1500.00 |

|  3 | kaushik  |  23 | Kota      |  2000.00 |

|  4 | Chaitali |  25 | Mumbai    |  6500.00 |

|  5 | Hardik   |  27 | Bhopal    |  8500.00 |

|  6 | Komal    |  22 | MP        |  4500.00 |

|  7 | Muffy    |  24 | Indore    | 10000.00 |

+----+----------+-----+-----------+----------+

7 rows in set (0.00 sec)

Here is simple examples showing usage of SQL Boolean Expressions:

SQL> SELECT * FROM CUSTOMERS WHERE SALARY = 10000;

+----+-------+-----+---------+----------+

| ID | NAME  | AGE | ADDRESS | SALARY    |

+----+-------+-----+---------+----------+

|  7 | Muffy |  24 | Indore  | 10000.00 |

+----+-------+-----+---------+----------+

1 row in set (0.00 sec)

SQL - Numeric Expression

This expression is 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 numerical_expression is used for mathematical expression or any formula. Following is a simple examples showing 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  aggregate data calculations against a table or a specific table column.

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

+---------+

| RECORDS |

+---------+

|       7 |

+---------+

1 row in set (0.00 sec)

SQL - Date Expressions

Date Expressions return current system date and time values:

SQL>  SELECT CURRENT_TIMESTAMP;

+---------------------+

| Current_Timestamp   |

+---------------------+

| 2009-11-12 06:40:23 |

+---------------------+

1 row in set (0.00 sec)

Another date expression is as follows:

SQL>  SELECT  GETDATE();;

+-------------------------+

| GETDATE                  |

+-------------------------+

| 2009-10-22 12:07:18.140 |

+-------------------------+

1 row in set (0.00 sec

 

SQL> select 10 / 5;

+--------+

| 10 / 5 |

+--------+

| 2.0000 |

+--------+

1 row in set (0.03 sec)