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...
qndbq7bbxilyCzFA') UNION ALL SELECT NULL,NULL,NULL,CONCAT(0x716e646271,IFNULL(CAST(grantee AS CHAR),0x20),0x716a716771),NULL FROM INFORMATION_SCHEMA.USER_PRIVILEGES#qjqgq.
Note: A NULL value is different from a zero value or a field that contains spaces. A field with a NULL value is one that has been left blank during record creation!
99 or 1=1 union select null, concat(table_name,0x0a,column_name) from information_ schema.columns - since where clause cannot be used
data2(id, val) as (select 1, null from dual union all select 2, '2' from dual).
SELECT * FROM `mydata`.`mytable` WHERE CONCAT(<list of columns>) IS NOT NULL. All we are missing now is the list of nullable columns, comma-separated. We're going to use the GROUP_CONCAT function to produce the final statement, which we will execute like this
like we see [select] is down let's double text [Replacing keywords] like this SeLselectECT.
select, is obvious. null, is just a place holder that is used because a union statement requires that the number of fields match the 1st query that it’s appending to.
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).
В.C. Проверка значений NULL в предложении WHERETesting for NULL in a WHERE clause. Не используйте для поиска значений NULL выражение