SELECT COUNT(*), 'null_tally' AS narrative FROM us WHERE a IS NULL UNION SELECT COUNT(*), 'not_null_tally' AS narrative FROM
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.
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...
The IS NULL operator is used to test for empty values (NULL values). The following SQL lists all customers with a NULL value in the "Address" field: Example. SELECT CustomerName, ContactName, Address FROM Customers WHERE Address IS NULL
Существуют специальные операторы IS NULL и IS NOT NULL, которые позволяют производить сравнения с NULLами.
Mapping to and from null. Null Propagates Through Expressions. Null in Aggregate Functions
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).
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...
...20NULL,version(),NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL
1 UNION ALL SELECT NULL,version()