Union select null, null, null, null, null, null, null from information_schema.tables. for a small database containing three tables. this instruction is used in sql injection I tried it and it worked but I didn't really know how it works can somebody help me...
Синтаксис: 0xHEX_ЧИСЛО (SM): SELECT CHAR(0x66) (S) SELECT 0x5045 (это не число, а строка) (M) SELECT 0x50 + 0x45
Coming to our discussion, NULL macro is defined as ((void *)0) in header files of most of the C compiler implementations. But C standard is saying that 0 is also a null pointer constant.
UNION ALL SELECT NULL, *, NULL, NULL FROM email. I understand what this does and why; the hacker needs to create a query that has the same number of columns as the query it's being merged with, and shifted around the * to make sure the emails are displayed. That's not my question.
However, this will return NULL provider results as well, how would I exclude all null results?
Как и в случае с обычными переменными, указатели не инициализируются при создании. Если значение не было присвоено, то указатель по умолчанию будет указывать на любой адрес, содержимым которого...
You should use IS NOT NULL. (The comparison operators = and <> both give UNKNOWN with NULL on either side of the expression.)
which covers (int *)0 as null pointer since cast is an explicit conversion (C11, 6.3) which is listed under conversion methods.
How can 0 be used for handling null pointers if that is the case?
IS NULL вернёт истину, если операнд имеет значение NULL и ложь, если он им не является.