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.
In postgres, I'm getting an error when I try to union two tables where one table has a column (Amount) containing double precision data type...
The Background I was trying to solve the fourth realistic mission in hackthissite.org, and couldn't figure out exactly what SQL I should inject into the URL to retrieve the list of emails.
Then in the second table I have select ..., null as opt from... I know that I could have an empty string with '' as
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...
What is the difference between … and … and why does the latter not work?
Above is two queries with their results merged by a UNION ALL clause. You will notice that the queries return different columns, one called 'departure' and one called 'arrival'.
Note: A NULL value is different from a zero value or a field that contains spaces.
Специальное значение NULL означает отсутствие данных, констатацию того факта, что значение неизвестно. По умолчанию это значение могут принимать столбцы и переменные любых типов, если только на них не наложено ограничение NOT NULL.