Chapter 8. Date Arithmetic
This chapter introduces techniques for performing simple date arithmetic. Recipes cover common tasks like adding days to dates, finding the number of business days between dates, and finding the difference between dates in days.
Being able to successfully manipulate dates with your RDBMS’s built-in functions can greatly improve your productivity. For all the recipes in this chapter, I try to take advantage of each RDBMS’s built-in functions. In addition, I have chosen to use one date format for all the recipes, “DD-MON-YYYY”. I chose to do this because I believe it will benefit those of you who work with one RDBMS and want to learn others. Seeing one standard format will help you focus on the different techniques and functions provided by each RDBMS without having to worry about default date formats.
This chapter focuses on basic date arithmetic. You’ll find more advanced date recipes in the following chapter. The recipes presented in this chapter use simple date data types. If you are using more complex date data types you will need to adjust the solutions accordingly.
8.1. Adding and Subtracting Days, Months, and Years
You need to add or subtract some number of days, months, or years from a date. For example, using the HIREDATE for employee CLARK you want to return six different dates: five days before and after CLARK was hired, five months before and after CLARK was hired, and, finally, five years before and after CLARK was hired. CLARK was hired ...