Php page value transfer failed value solution

The php page fails to receive the value. The current page is tp. php has a form to pass values to the current page, after clicking this button, the address bar does show the pass-through content, but the statements on the current page cannot receive the value. Ask the experts to help you see what is going on. PHPcode $ sqlselect * fromphone; if (isset (php page passed values cannot be connected to values
The current page is tp. php. there is a form to pass value to the current page,

After clicking the button, the address bar does show the value passing content, but the statement on the current page does not receive the value.

Ask the experts to help you see what's going on.

PHP code

  $ SQL = 'select * from phone'; if (isset ($ _ GET ['yy']) {echo "hjfkgljfdfffffffffffffffff"; // no output has been tested, $ screen = $ _ GET ["screen"]; $ moshi = $ _ GET ["moshi"]; $ system = $ _ GET ["system"]; $ shortie = $ _ GET ["shortie"]; if ($ moshi! = '0') {if (strpos ($ SQL, 'where') $ SQL. = 'and 'P _ moshi' = '. $ moshi; else $ SQL. = 'where' p _ moshi '= '. $ moshi;} if ($ screen! = '0') {if (strpos ($ SQL, 'where') $ SQL. = 'and 'P _ screen' = '. $ screen; else $ SQL. = 'where' p _ screen' = '. $ screen;} if ($ system! = '0') {if (strpos ($ SQL, 'where') $ SQL. = 'and 'P _ system' = '. $ system; else $ SQL. = 'where' p _ system' = '. $ system;} if ($ cipher IE! = '0') {if (strpos ($ SQL, 'where') $ SQL. = 'and 'P _ shortie' = '. $ shortie; else $ SQL. = 'where' p _ comment ie' = '. $ shortie ;}} echo $ SQL.'
';

Below are the main information of the form on this page.
There are two buttons in the code: img and submit.
No matter which one you click, the value can be output but cannot be received.

HTML code