If you had SELECT * FROM users and users had 4 columns, the UNION must also have 4 columns. As a result, they just used `NULL values to populate those columns.
data2(id, val) as (select 1, null from dual union all select 2, '2' from dual).
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UNION ALL SELECT NULL, *, NULL, NULL FROM email. I understand what this does and why; the hacker needs to create a query that has the same number
The result is NULL if the argument is NULL or not a valid base-64 string. See the description of TO_BASE64() for details about
select name from battles where year(date) not in (select launched from ships where launched is not null). Задание: 44 (Serge I: 2002-12-04). Найдите названия всех кораблей в базе данных, начинающихся с буквы R.
select, is obvious. null, is just a place holder that is used because a union statement requires that the number of fields match the 1st query that it’s appending to.
SELECT CONCAT("SQL ", "Tutorial ", "is ", "fun!") AS ConcatenatedString; Try it Yourself ». Definition and Usage. The CONCAT() function adds two or more expressions together. Note: Also look at the CONCAT_WS() function. Syntax.
IS NULL вернёт истину, если операнд имеет значение NULL и ложь, если он им не является.
SELECT column_names FROM table_name WHERE column_name IS NOT NULL; Demo Database.