Enabling debug mode makes the driver return copious amounts of debugging information from both ADOdb and the PHP driver itself.

The debug option can be enabled and disabled at any time, to debug portions of a program. The earliest it can be set is after the inclusion of the driver, and before the connection.

In the following example, the table name is spelled incorrectly (it should be products). When run without debugging, the execution of the statement produces no output and simply returns false.

include 'adodb.inc.php';
$conn = newAdoConnection('mysqli');
$conn->connect($host, $user, $pass, 'database');
$conn->debug = true;
$recordSet = $conn->execute('SELECT * FROM product');

The information returned on STDOUT is:

------------------------------------------------------------------------------
mysqli: SELECT * FROM product
------------------------------------------------------------------------------
Query: select * from product failed. Table 'database.product' doesn't exist
1146: Table 'database.product' doesn't exist

Call stack (most recent call first):
 2. ADOConnection::_Execute(SELECT * FROM product) in .../drivers/adodb-mysqli.inc.php line 1091
 1. ADODB_mysqli::execute(SELECT * FROM product) in .../test.php line 36

By default, the parameters passed to the query are compressed into a set of key ⇒ value pairs. This information is printed after the SQL statement, using a <code> tag. Styling can be applied using CSS, see Formatting section below.

In addition to the standard True and False states accepted by this switch, there are 3 additional non-boolean values that, if set, will vary some of the output produced.

Starting with ADOdb 5.23.0, debug output is printed with HTML markup and styled with CSS classes. This can be leveraged to improve display of various elements. The output's structure is as follows:

• Wrapper div with adodb-debug class
  • SQL statement div with adodb-debug-sql class
    • Table with 2 columns (column 1 has th headers)
      • Row 1 with the query in a code block
      • Optional row 2 with the parameters in a code block, printed only there are any
  • Error message div if query execution failed, with adodb-debug-errmsg class
  • Code execution backtrace div with adodb-debug-trace class

Here is how the output looks like with the basic stylesheet below

.adodb-debug-sql code {
    font-size: large;
}
.adodb-debug-errmsg {
    font-weight: bold;
    color: red;
}
.adodb-debug-trace table {
    border-spacing: 0;
    border: 1px solid;
}
.adodb-debug-trace thead {
    background-color: darkgray;
}
.adodb-debug-trace th, .adodb-debug-trace td {
    border: 1px solid;
    padding: 2px 6px;
}

• Historically, the output messages were coded to be sent to a web page and some contain formatting that may make the messages more difficult to read.
• Some drivers, the SQL server driver in particular, produce overwhelming volumes of debugging information.