With few exceptions, characters 0 to 127 are the same for all the code pages. The mapping for this range of characters is called the ASCII character set. It includes the English language alphabet in upper and lowercase, and common punctuation symbols and the digits. This range is often called the seven-bit range (because only seven bits are needed to represent the numbers up to 127) or the lower page. The characters from 128 to 255 are called extended characters, or upper code page characters, and vary from one code page to another.

Problems with code page compatibility are rare if the only characters used are from the English alphabet, as these are represented in the ASCII portion of each code page (0 to 127). However, if other characters are used, as is generally the case in any non-English environment, there can be problems if the database and the application use different code pages.

For example, suppose a database using the UTF-8 character set loads a table from a file containing cp1252 data, and the encoding is not specified as cp1252 on the LOAD TABLE statement. Because the encoding is not specified, the data is assumed to be encoded in UTF-8, so no character conversion takes place; the cp1252 encoding is stored directly in the database. This means that characters such as the euro symbol, represented in cp1252 as hex 80, are not converted into UTF-8. The euro symbol in UTF-8 is represented by the three-byte sequence E2 82 AC, but, in this case, is stored in the database as 80. Subsequently, when an application requests data, the database server attempts to convert the data from UTF-8 to the client character set. The conversion produces corrupted characters.