C# - syntax error: missing operand after 'unary' operator

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I have a problem running this code that I get from youtube. I tried everything but it keeps me getting this error. Can anybody help me?

What I have tried:

string strTextBox1 = TextBox1.Text.Trim().ToString();
            StringBuilder sb = new StringBuilder();
            sb.AppendFormat("( Convert (ID, 'System.String) LIKE '" + " {0} " + "')", strTextBox1);
            sb.AppendFormat("OR(FacilityName LIKE '*" + "{0}" + "*')", strTextBox1);

Posted 29-Jan-20 21:29pm

Member 14716708

Updated 4-Feb-20 12:51pm

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jimmson 30-Jan-20 3:39am

If you're getting some syntax error, it's not from the code you posted.
I don't have any problem to compile it.

phil.o 30-Jan-20 5:51am

string strTextBox1 = TextBox1.Text.Trim().ToString();
Why are you calling ToString() method on something which already is a string?

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OriginalGriff · Answer 1 · 2020-01-29T21:41:00

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:

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?
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 ...

Patrice T · Answer 2 · 2020-02-04T12:52:00

C#

string strTextBox1 = TextBox1.Text.Trim().ToString();
StringBuilder sb = new StringBuilder();
sb.AppendFormat("( Convert (ID, 'System.String) LIKE '" + " {0} " + "')", strTextBox1);
sb.AppendFormat("OR(FacilityName LIKE '*" + "{0}" + "*')", strTextBox1);

Not a solution to your question, but another problem you have.
Never build an SQL query by concatenating strings. Sooner or later, you will do it with user inputs, and this opens door to a vulnerability named "SQL injection", it is dangerous for your database and error prone.
A single quote in a name and your program crash. If a user input a name like "Brian O'Conner" can crash your app, it is an SQL injection vulnerability, and the crash is the least of the problems, a malicious user input and it is promoted to SQL commands with all credentials.
SQL injection - Wikipedia[^]
SQL Injection[^]
SQL Injection Attacks by Example[^]
PHP: SQL Injection - Manual[^]
SQL Injection Prevention Cheat Sheet - OWASP[^]
How can I explain SQL injection without technical jargon? - Information Security Stack Exchange[^]

Advice: when you compose a query that don't work, first print the resulting query that you send to server, it can help to see where is the syntax error.

C# - syntax error: missing operand after 'unary' operator

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