php constant expression contains invalid operations

1Parse error: syntax error, unexpected 'if' (T_IF) in C:\xampp\htdocs\study\insertdata.php on line 5

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2From the official Php documentation :
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4Like any other PHP static variable, static properties may only be initialized using a literal or constant before PHP 5.6; expressions are not allowed. In PHP 5.6 and later, the same rules apply as const expressions: some limited expressions are possible, provided they can be evaluated at compile time.
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6So you cannot initialize a static variable with another variable. Replace $appdata['id'] with a constant string or remove the static attribute.
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8This is because all static declarations are resolved in compile-time, when the content of other variables is not known (see this other page of official doc).