If I have the table … This will display Firstname-Middlename-Surname e.g. … The second one (Jane’s) displays correct, however since John doesn’t have a middlename, I want it to ignore the second dash.
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...
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).
SELECT column_names FROM table_name WHERE column_name IS NOT NULL
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CONCAT_NULL_YIELDS_NULL control whether concatenation results shall be treated as NULL or empty string values.
This MySQL IS NULL example will return all records from the contacts table where the last_name contains a NULL value.
To determine whether an expression is NULL, use IS NULL or IS NOT NULL instead of comparison operators (such as = or !=).
NULL может размещаться в поле любого типа. Тем не менее, NULL, как NULL-значение, часто используется в SQL.
NULL is special in SQL. NULL indicates that the data is unknown, inapplicable or even does not exist.