Chapter 5 - Character Data Types in SQL

Abstract

Different programming languages handle strings differently. In Structured Query Language (SQL), character strings are printable characters enclosed in single quotation marks. SQL uses two apostrophes together to represent a single apostrophe in a string literal. Double quotation marks are reserved for column names that have embedded spaces or that are also SQL-reserved words. Character sets fall into three categories: (1) those defined by national or international standards, (2) those provided by implementations, and (3) those defined by applications. All character sets contain the <space> character. No two languages agree on how to compare character strings as equal unless they are identical in length and match exactly—position for position, character for character. The original SQL-89 standard did not define any functions for CHAR (n) data types. Standard SQL added the basic functions that have been common to implementations for years. The catalog number of a book often needs to reduce an author's name to a simple fixed-length code. While the results of a Cutter table look much like those of a Soundex, their goal is different. Cutter tables have two important properties: (1) they preserve the alphabetical ordering of the original name list, which means that a rough sort can be done on them and (2) each grouping tends to be of approximately the same size as the set of names gets larger.