$url = "show.php catid=". ($row [' catid ']); please advise

$url = "show.php catid=". ($row [' catid ']);

When this code executes, does it automatically invoke the contents of show.php??? The middle of this? Catid= can be written casually, such as written $url = "show.php?topic=". ($row [' catid ']);

Reply to discussion (solution)

This just generates a string for the link only, the user clicks to run Shop.php...catid casually, but the variable names in the shop.php file are consistent

? id= ". row[' catid ']";

The ID can be arbitrarily defined, but row[' catid ' should be the only
When passing a value, it depends on the parameter.

$url = "show.php catid=". ($row [' catid ']);
This code is the $url assignment, the value is a string, the content is show.php?catid= $row [' catid '] content

There is no content to invoke show.php.
CATID is a parameter name that can be written casually, but the page that gets the parameter is modified accordingly.
For example show.php?catid=1 so show.php need to get $_get[' catid ']
If show.php?id=1 so show.php need to get $_get[' ID ']

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