Discovering SQL: A Hands-On Guide for Beginners

CONVERSION FUNCTIONS

Earlier in the book we discussed why all data cannot be just text and proposed specific data types as a solution. This presents a new problem: conversion between different data types. Sometimes it becomes necessary to convert one data type to another. For example, in some RDBMS implementations, the CONCAT function requires all members to be converted into strings before they can be concatenated. The permutations of the different data types need to be converted into each other before they can be manipulated: numbers to strings, and strings to numbers, dates to string and back, the applications are virtually endless. This is what conversion functions are good at. As it becomes clearer that English, while important, is not the only language on Earth, there is an ever-increasing demand for national character databases. Conversion functions might provide translation for English character–based data, so it can be correctly represented in the character set of other alphabets. Some of the most common conversion functions for three major RDBMSs—Oracle, SQL Server, and IBM DB2—are listed in Table 4-6.

TABLE 4-6: Conversion Functions

Sometimes a RDBMS converts data implicitly from one type to another. While this feature might be convenient, it is also something to worry ...