Never do it like that! 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. Use Parametrized queries instead.
When you concatenate strings, you cause problems because SQL receives commands like:
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:
SELECT * FROM MyTable WHERE StreetAddress = 'x';DROP TABLE MyTable;
Which SQL sees as three separate commands:
SELECT * FROM MyTable WHERE StreetAddress = 'x';
A perfectly valid SELECT
DROP TABLE MyTable;
A perfectly valid "delete the table" command
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?
And your SQL indicates deeper flaws: You take a DateTime value, convert it to a string in your C# code, then use SQL to convert that string to ... a string, which you then try to use as a Date in a BETWEEN statement. That implies that your order_date column is a string, which means that your BETWEEN will fail, as it uses string comparisons which stop at the first different character in the two strings. So
'31-01-1900' is after '01-12-2017' because '3' is after '0' in the character set, and SQL will stop looking at that point.
Change your DB to use DATE, DATETIME, or DATETIME2 to store your dates, and pass the DateTime value directly via a parameterised query while you fix all the other concatenations in your application!
Then you can explain what "split my column" actually means ... but that will have to wait until you have a "safe" code base to work from...
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