What is that quote doing in there?
sb.AppendFormat("( Convert (ID, 'System.String) LIKE '" + " {0} " + "')", strTextBox1);
^
|
It has no matching quote...
Add to that, whoever wrote teh code you don;t understand is ... um ... an idiot.
It can be simplified first to this:
sb.AppendFormat("( Convert (ID, System.String) LIKE ' {0} ')", strTextBox1);
which is a lot more readable (and the same for your second string) or more modernly like this:
sb.AppendFormat($"( Convert (ID, System.String) LIKE ' {strTextBox1} ')");
But... if that is going anywhere near SQL, then don't do 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. Always use Parameterized 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 secondly, comparing numbers as strings is a very poor idea as string comparisons work by comparing the first different pair of characters in the two strings: so teh sort order is
1
10
11
12
...
19
2
20
21
...
Not the order you'd expect.
I'd wonder about the competence of whoever created the YouTube video - but that's no surprise most of 'em are created by people who know nothing about creating videos, and even less about the subject they are covering ...