MySQL, id = $GET [' ID '] returns a null result. How to fix it

MySQL, id = $GET [' ID '] returns a null result.
The database ID entry is bigint

PHP Code:

SELECT * FROM mytable WHERE id= ' ". $GET [' id ']." '

Sometimes the results can be displayed, and sometimes the results are empty. The empty MySQL query statement is pasted into phpMyAdmin sql, which can be displayed normally.
Suspect that the $GET [' ID '] item was mistakenly considered by PHP as a string, not an int,

So add

SELECT * FROM mytable WHERE id= ' ". (int) ($GET [' ID ']). "'

The result is still empty. How to solve the problem?

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If the ID is shaped, you don't need to add a single quote, the string needs Ah!
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$GET if it's a GET method, it should be $_get.

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Cast to shaping should be intval ($_get[' id ');
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$GET if it's a GET method, it should be $_get.

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