PHP Queries

Languages - PHP
Queries

Before running a query, your program must first connect to the database. Using the query results is covered separately and assumes that you already know what is described on this page.

Using MySQL, queries are fairly simple.

$result_set = mysql_query("select * from tablename");

However, I prefer a significantly more complex method

It should show an error if it fails
It should be able to print the sql statement if a debug flag is set
Since this uses a function, it will contribute to the trace that is displayed only if another debug flag is set

This is a suggested call sequence - because white space is ignored, the query string is broken up onto several lines to improve readability. The final close quote and semicolon are placed on a line by themselves to simplify adding additional lines.

  $query = "
    select * 
    from subjects
    order by position
         ";

  $subject_set = mc_query($query);

This is the function - while still simple, it does a lot.

\n produces a newline in the html file and helps when reading it
\$ displays a dollar sign and keeps the value of the variable from being displayed
$debug_str .= "some string"; // adds the string to the existing value
<pre> makes it easier to read the output
The query itself is not placed in the trace string unless there is an error

Full details of the debug architecture are presented at Debug Tips. The following summarizes the important variables.

// 0 means - do not print debug output

$debug       =  0; // print when subroutine starts
$debug_query =  0; // print query strings
$debug_trace =  0; // print $debug_str at end of output
$debug_str   = ""; // every subroutine adds to this

The idea is to set the 3 control variables based on command line (url) parameters.

Author: Robert Clemenzi

Languages - PHP Queries

URL: http:// mc-computing.com / Languages / PHP / Queries.html

Languages - PHP
Queries