Question about php ifelse?

Php ifelse question ??? I am a newbie. today I am modifying a PHP source code because I want to use a PHP IFelse. I hope you can help me. Link. php? Id = abc when the value of id is null when no abc is found, the system prompts that the parameter is incorrect. if the value of id is not empty, the question of if else in php is ???
I am a newbie. today I am modifying a PHP source code because I want to use a php if else. I hope you can help me.

Link. php? Id = abc when no abc is available, that is, if the value of id is null, the system prompts that the parameter is incorrect. if the value of id is not empty, link. php is executed? Id = abc

How to write this statement?

------ Solution --------------------
If (isset ($ _ GET ['id']) {
// Has an id

} Else {
// No id prompt code
}
------ Solution --------------------

PHP code

If (isset ($ _ GET ['id']) {// Has id} else {// No id prompt code}