ZEND PHP 5 Certification STUDY GUIDE

144 ” Database Programming
SQL supports a number of data types, which provide a greater degree of flexibility
than PHP in how the data is stored and represented. For example, numeric values
can be stored using a variety of types:
int or integer
smallint
real
float
Signed integer number, 32 bits in length.
Signed integer number, 16 bits in length.
Signed floating-point number, 32 bits in length.
Signed floating-point number, 64 bits in length.
To these, most database systems add their own, non-standard variants—for example,
MySQL supports a data type called tinyint, which is represented as a one-byte
signed integer number. Clearly, all of these data types are converted into either integers
or floating-point numbers when they are retrieved into a PHP variable, which is
not normally a problem. However, you need to be aware of the precision and range
of each data type when you write data from a PHP script into a database table, since
it’s quite possible that you will cause an overflow (which a database system should
at least report as a warning).
This is even more apparent—and, generally, more common—when you deal with
string data types. SQL-92 defines two string types:
char
varchar
Fixed-length character string.
Variable-length character string.
The only difference between these two data types is in the fact that a char string
will always have a fixed length, regardless of how many characters it contains (the
string is usually padded with spaces to the column’s length). In both cases, however,
a string column must be given a length (usually between 1 and 255 characters, although
some database systems do not follow this rule), which means that any string
coming from PHP, where it can have an arbitrary length, can be truncated, usually
without even a warning, thus resulting in the loss of data.
Most database systems also define an arbitrary-length character data type (usually
called text) that most closely resembles PHP’s strings. However, this data type usually
comes with a number of strings attached (such as a maximum allowed length
and severe limitations on search and indexing capabilities). Therefore, you will still
be forced to use char and (more likely) varchar, with all of their limitations.
Strings in SQL are enclosed by single quotation strings:
Licensed to 482634 - Amber Barrow (itsadmin@deakin.edu.au)