36 lines
3.4 KiB
HTML
36 lines
3.4 KiB
HTML
|
<html><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8"><title>Reading data from a database</title><link rel="stylesheet" type="text/css" href="manual.css"><meta name="generator" content="DocBook XSL Stylesheets V1.76.0"><link rel="home" href="index.html" title="JpGraph Manual"><link rel="up" href="ch13.html" title="Chapter 13. Getting hold of the data to be displayed"></head><body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">Reading data from a database</th></tr><tr><td width="20%" align="left"> </td><th width="60%" align="center">Chapter 13. Getting hold of the data to be displayed</th><td width="20%" align="right"> </td></tr></table><hr></div><div class="sect1" title="Reading data from a database"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id2538964"></a>Reading data from a database</h2></div></div></div>
|
|||
|
|
|
|||
|
|
<p>Since there are so many databases and so many ways to organize data in tables it
|
|||
|
|
is impossible to give generic examples. Instead we point out some common pitfalls
|
|||
|
|
when gathering data from a database.</p>
|
|||
|
|
<p>
|
|||
|
|
</p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem">
|
|||
|
|
<p>Make sure the data is valid numeric data. It is a common mistake to
|
|||
|
|
read <code class="code">NULL</code> (or empty strings "") values and try to plot
|
|||
|
|
them. Beware that the PHP function <code class="code">empty()</code> also will return
|
|||
|
|
true for 0 and "0" values so it is not enough to just test with
|
|||
|
|
<code class="code">empty()</code> since this will also remove all values that
|
|||
|
|
happens to be valid 0 values. To avoid this use the following modified
|
|||
|
|
empty method.</p>
|
|||
|
|
<p>
|
|||
|
|
</p><div class="hl-main"><table class="hl-table" width="100%"><tr><td class="hl-gutter" align="right" valign="top"><pre>1
|
|||
|
|
2
|
|||
|
|
3
|
|||
|
|
4
|
|||
|
|
5
|
|||
|
|
</pre></td><td class="hl-main" valign="top"><pre><span class="hl-code">function empty0($aValue){
|
|||
|
|
if ( !is_numeric(trim($aValue)) )
|
|||
|
|
return empty($aValue);
|
|||
|
|
return false;
|
|||
|
|
}</span></pre></td></tr></table></div><p>
|
|||
|
|
</p>
|
|||
|
|
</li><li class="listitem">
|
|||
|
|
<p>Some databases (e.g. MySQL) returns a column with decimal type values
|
|||
|
|
as string in a SELECT statement which normally is handled by automatic
|
|||
|
|
conversion in PHP but since PHP has different interpretation of "0.00"
|
|||
|
|
and 0.00 in respect to what is interpreted as empty or not this needs to
|
|||
|
|
be carefully handled.</p>
|
|||
|
|
</li></ul></div><p>
|
|||
|
|
</p>
|
|||
|
|
</div><div class="navfooter"><hr><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"> </td><td width="20%" align="center"><a accesskey="u" href="ch13.html">Up</a></td><td width="40%" align="right"> </td></tr><tr><td width="40%" align="left" valign="top"> </td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top"> </td></tr></table></div></body></html>
|