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.
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...
...1 from(select count(*),concat((select (select (select distinct concat(0x7e,0x27,unhex(Hex(cast
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
11223344) UNION SELECT NULL,NULL,NULL,NULL WHERE 1=2 –- Если нет ошибки, значит синтаксис верный, т.е. используется
SELECT header, txt FROM news UNION ALL SELECT name, pass FROM members This will combine results from both news table and members table
...null from information_schema.columns where table_name='foundtablename' LIMIT 0,1
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).
mysql> SELECT NULL, 1+NULL, CONCAT('Invisible',NULL); To search for column values that are NULL, you cannot use an expr = NULL test. The following statement returns no rows, because expr = NULL is never true for any expression: Press CTRL+C to copy. mysql> SELECT * FROM my_table...
IS NULL вернёт истину, если операнд имеет значение NULL и ложь, если он им не является.