Click here to Skip to main content
15,889,909 members
Please Sign up or sign in to vote.
0.00/5 (No votes)
See more:
"delete from employees where empname=N'" & TxtList.Item("Employee Name", TxtList.CurrentRow.Index).Value & "'"
this my delete query i want delete columns of multiple tables

What I have tried:

i have tried with begin but not working
Posted
Updated 27-Jul-18 23:19pm

1 solution

That doesn't delete columns, that deletes rows.
Columns -->   ID    Name          Address
Rows v
                  1    Joe Smith     2 Bread Street
                  2    Mike Hunt     42, Ballard way
                 ...
Delete a column, and it removes all the data in that column for all rows, you don't get a WHERE clause with that!

And don't do anything like you show in your query! Never concatenate strings to build a SQL command. It leaves you wide open to accidental or deliberate SQL Injection attack which can destroy your entire database. Always use Parameterized queries instead.

When you concatenate strings, you cause problems because SQL receives commands like:
SQL
SELECT * FROM MyTable WHERE StreetAddress = 'Baker's Wood'
The quote the user added terminates the string as far as SQL is concerned and you get problems. But it could be worse. If I come along and type this instead: "x';DROP TABLE MyTable;--" Then SQL receives a very different command:
SQL
SELECT * FROM MyTable WHERE StreetAddress = 'x';DROP TABLE MyTable;--'
Which SQL sees as three separate commands:
SQL
SELECT * FROM MyTable WHERE StreetAddress = 'x';
A perfectly valid SELECT
SQL
DROP TABLE MyTable;
A perfectly valid "delete the table" command
SQL
--'
And everything else is a comment.
So it does: selects any matching rows, deletes the table from the DB, and ignores anything else.

So ALWAYS use parameterized queries! Or be prepared to restore your DB from backup frequently. You do take backups regularly, don't you?

Fix that through your whole app, and then think about how the table data you want to delete is organised and related: we can't help you at the moment because we have no idea how your DB is laid out.
 
Share this answer
 

This content, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)



CodeProject, 20 Bay Street, 11th Floor Toronto, Ontario, Canada M5J 2N8 +1 (416) 849-8900