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 works can somebody help me...
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.
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.
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..?
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'.
A field with a NULL value is a field with no value. If a field in a table is optional, it is possible to insert a new record or update a record without adding a value to this
SQL’s NULL indicates absent data. NULL propagates through expressions and needs distinct comparison operators.
Параметр SET CONCAT_NULL_YIELDS_NULL должен быть в состоянии ON при создании или изменении индексов в вычисляемых столбцах