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)