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...
Select char_length(cast('123456789 1' as varchar(10))) from rdb$database. Получаем: Exception ... string truncation Т.е. пробел мы обрезать можем, а другие символы нет. Так и должно быть или нет?
Then in the second table I have select ..., null as opt from... I know that I could have an empty string with '' as opt however, I don't want an empty
A NULL column is not countable, however a row that has a NULL column is.
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
How can I run a MySQL query that selects everything that is not null? It would be something like … Do I just remove the all and go..?
The null character (also null terminator or null byte), abbreviated NUL or NULL, is a control character with the value zero.
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 -- test all nulls