When you want to replace a possibly null column with something else, use IsNull.
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...
UNION ALL SELECT NULL, *, NULL, NULL FROM email. I understand what this does and why
If a null pointer constant is converted to a pointer type, the resulting pointer, called a null pointer, is guaranteed to compare unequal to a pointer to any object or function.
...1), null, null,NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULl, NULL-- Можно использовать CAST() или
An uninitialized pointer can be null or non-null (or "both" or "neither"), and relying on predictable behaviour when using it is a bad idea. – chris May 9 '15 at 4:22. @chris, but if I use "string* s" then it always prints an andress like "0x401dee" – lxdthriller May 9 '15 at 4:26.
It should be noted that NULL pointer is different from an uninitialized and dangling pointer.
NULL в языках программирования Си и C++ — макрос, объявленный в заголовочном файле stddef.h (и других заголовочных файлах). Значением этого макроса является зависящая от реализации константа нулевого указателя (англ. null pointer constant).
Существуют специальные операторы IS NULL и IS NOT NULL, которые позволяют производить сравнения с NULLами. IS NULL вернёт истину, если операнд имеет значение NULL и ложь, если он им не является.
A field with a NULL value is a field with no value. If a field in a table is optional, it is possible to insert a new record or update a record without adding a value to this field.