If I have the table … This will display Firstname-Middlename-Surname e.g. … The second one (Jane’s) displays correct, however since John doesn’t have a middlename, I want it to ignore the second dash.
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...
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
CONCAT() returns NULL if any argument is NULL. mysql> SELECT CONCAT('My', 'S', 'QL')
Предикат IS NULL позволяет проверить отсутствие (наличие) значения в полях таблицы. Использование в этих случаях обычных предикатов сравнения может привести к неверным результатам, так как сравнение со значением NULL дает результат UNKNOWN (неизвестно).
SQL supports NULL, a special value that is employed to represent the values of attributes that will be unknown or not apply to a tuple.
CONCAT_NULL_YIELDS_NULL control whether concatenation results shall be treated as NULL or empty string values.
Like this? select fielda, case when exists (select 1 from #tmp where fieldb is null and fielda = a.fielda) then null else sum(fieldb) end, min(fieldb) from #tmp a group by
Когда значение поля есть NULL — это значит, что программа базы данных специальным образом помечает поле, как не содержащее какого-либо значения для
-999.9+union+all+select+%27R3DM0V3_hvj_injection',null%2CNULL%2CNULL%2CNULL%2CNULL%2CNULL%2CNULL%2CNULL%2CNULL%2CNULL