This section covers the computational features of Texis. They are adequate to allow the user to perform computations on the data and/or retrieve rows based on conditions involving computations. For example, you can adjust salaries for a 5 percent across-the-board increase, or you can compute weekly salaries (i.e., salary divided by 52).
Arithmetic calculations are performed on fields, or columns, in the database. An arithmetic expression is used to describe the desired computation. The expression consists of column names and numeric constants connected by parentheses and arithmetic operators. Table here shows the arithmetic operators used in Texis.
|Arithmetic Operation||Texis Operator||Example|
|Addition|| || |
|Subtraction|| || |
|Multiplication|| || |
|Division|| || |
Typically, the arithmetic expression is used in the
SELECT clause to
perform calculations on data stored in the table.
Example: Next year every employee will receive a 5 percent salary increase. List the names of each employee, his or her current salary, and next year's salary.
Enter this statement:
SELECT ENAME, SALARY, SALARY * 1.05
FROM EMPLOYEE ;
SALARY * 1.05" is the arithmetic expression.
The results are:
ENAME SALARY SALARY * 1.05
Aster, John A. 32000 33600
Barrington, Kyle 45000 47250
Chapman, Margaret 22000 23100
Jackson, Herbert 30000 31500
Price, Stella 42000 44100
Sanchez, Carla 35000 36750
Smith, Roberta 25000 26250
The expression "
SALARY * 1.05" results in each value in the
salary column being multiplied by 1.05. The results are then
displayed in a new column that is labeled
SALARY * 1.05.
If more than one arithmetic operator is used in an arithmetic
expression, parentheses can be used to control the order in which the
arithmetic calculations are performed. The operations enclosed in
parentheses are computed before operations that are not enclosed in
parentheses. For example, the expression:
12 * (SALARY + BONUS)
means bonus is added to salary, and then this result is multiplied by
If parentheses are omitted or if several operations are included within the parentheses, the order in which calculations are performed is as follows:
For example, in the expression:
SALARY + SALARY * .05
the value in the SALARY column is multiplied by .05, and then the
salary value is added to this intermediate result.
When two or more computations in an expression are at the same level
(e.g., multiplication and division), the operations are executed from
left to right. For example, in the expression:
SALARY / 12 * 1.05
the salary value is first divided by 12, and then this result is
multiplied by 1.05.
Arithmetic calculation can also be used in a
WHERE clause to select
rows based on a calculated condition. In addition, arithmetic
expressions can be used in the HAVING and ORDER BY clauses, which will
be discussed in later sections of this chapter.
Example: List the names of all employees earning a monthly salary above $3000.
WHERE (SALARY/12) > 3000 ;
The rows in the
EMPLOYEE table are retrieved if the condition "salary
divided by 12" is greater than $3000. This was true only for
Barrington and for Price, whose annual salaries (respectively $45,000
and $42,000) are greater than $3000 when divided by 12 months.