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Problem with db.Database.SqlQuery() usage in C#

I am a newbie in C#. I wrote a code as below
TestDBEntities db = new TestDBEntities();
string data = db.Database.SqlQuery<string>("select PASSWORD from User where USERNAME='admin'").FirstOrDefault();
When I execute this code, an error appears:
Incorrect syntax near the keyword 'User'
Why did this happen? I already have a table named "User".
Thanks for the comments.

Change you sql query to below code:
"select [PASSWORD] from [User] where [USERNAME]='admin'"
and let us know, which database are you using? (SQL Server or MySQL or ...)
"And avoid naming your DB tables, columns, etc. using reserved keywords"

User is a typical SQL reserved word.
Not a good practice to use SQL reserved words for a table name.
A list of reserved words here: https://www.drupal.org/docs/develop/coding-standards/list-of-sql-reserved-words

What's causing this syntax error? oledb INSERT statement

I posted about a different issue I had earlier, and with some help resolved that.
I am now receiving a syntax error centered around the following code:
importConnection.Open();
Console.WriteLine("Foxpro connection open");
OleDbCommand deleteOleDbCommand = new OleDbCommand(#"TRUNCATE TABLE CLIENT",
importConnection);
Console.WriteLine("writing to table");
Console.ReadKey();
using (OleDbCommand importCommand = new OleDbCommand(
string.Format("INSERT INTO CLIENT (Title,Fname,Sname)" + "VALUES ({0},{1},{2})",
exportReader.GetValue(0), exportReader.GetValue(1), exportReader.GetValue(2))))
importCommand.ExecuteReader();
With this being the output:
Output Text
using break points I have determined that the export reader calls are receiving data. I've narrowed it down to an issue with:
"VALUES ({0},{1},{2})",
exportReader.GetValue(0), exportReader.GetValue(1), exportReader.GetValue(2))))
I have confirmed that data can be inserted by doing the following:
using (OleDbCommand importCommand =
new OleDbCommand(string.Format(
"INSERT INTO CLIENT (Title,Fname,Sname)" + "VALUES (Mr,Joshua,Cameron-Mackintosh)",
importConnection)))
This causes no problems, so I know the issue does not lie with the underlying connection or command.

Others correctly comment about SQL-Injection, however VFP is less impacted to SQL-Injection, it can be just the same. Main reason, VFP doesn't really work with multiple queries the same way other sql engines allow by a ";" identifying break between statements. However, with mismatched quotes, it CAN and WILL break your sql-statements from actually running.
Having said that, VFP OleDb provider does allow parameterizing, but does so without "named" parameters. It does it with "?" as a place-holder for where the value would be inserted by the .net framework, and you don't have to convert the data type as long as it is in the same expected format (ex: string, numeric, date)
change your OleDbCommand to
"INSERT INTO CLIENT (Title, Fname, Sname ) values ( ?, ?, ? )"
Then, set your parameters via
importCommand.Parameters.Add( "parmForTitle", exportReader.GetValue(0));
importCommand.Parameters.Add( "parmForFName", exportReader.GetValue(1));
importCommand.Parameters.Add( "parmForSName", exportReader.GetValue(2));
Also, the parameters must be added in the exact same sequential order as they appear in the query. So, I prefixed them with "parmFor" to indicate it is the parameter placement for the corresponding field being inserted (or updated, or used in select, insert or delete too). The command objects work the same for all the commands. Even if you write a select statement and have values in a WHERE, JOIN or whatever other position.
THEN, ExecuteNonQuery()

It is saying "foxpro connection string" there. If it is done against
a VFP database, then "Truncate table client" wouldn't work in the
first place. That command does not exist in VFP. Instead you could
try using "Delete From Client" which marks the records for deletion.
Or you can use "zap" command with ExecSript that would correspond to
"truncate table" but then the connection needs to use the table
exclusively.
You should quote the string values. Better yet, for any SQL operation you should use parameters. When you use parameters, you should do that in a correct way for the connection you use. Here you are using an OLEDB connection, then you should use ? as a parameter place holder.
A revised version of your code would then be:
importConnection.Open();
Console.WriteLine("Foxpro connection open");
OleDbCommand deleteOleDbCommand = new OleDbCommand(#"Delete from CLIENT",
importConnection);
Console.WriteLine("writing to table");
Console.ReadKey();
using (OleDbCommand importCommand = new OleDbCommand(
#"INSERT INTO CLIENT (Title,Fname,Sname) VALUES (?,?,?)",
importConnection))
{
importCommand.Parameters.AddWithValue("title","");
importCommand.Parameters.AddWithValue("fname","");
importCommand.Parameters.AddWithValue("sname","");
// maybe in a loop here
importCommand.Parameters["title"].Value = exportReader.GetValue(0);
importCommand.Parameters["fname"].Value = exportReader.GetValue(1);
importCommand.Parameters["sname"].Value = exportReader.GetValue(2);
importCommand.ExecuteNonQuery();
// ...
}
PS: You could directly feed the values on the Parameters.AddWithValue instead of creating a separate .Parameters["..."].Value = ... but then you would only be able to do that for a single insertion (not something related to VFP, it is the case for OleDb or Sql or whatever).

You don't need ExecuteReader for an insert statement. Just use ExecuteNonQuery.
In your case, if your columns are character typed, you need to use single quotes with them for example;
VALUES ('{0}', '{1}', '{2}')
Also use white space (not have to but as a good practice) before VALUES part.
"INSERT INTO CLIENT (Title,Fname,Sname)" + " VALUES (Mr,Joshua,Cameron-Mackintosh)",
// ^^^ here
But more important;
You should always use parameterized queries. Prepared statements automatically handle for escape characters for example and this kind of string concatenations are open for SQL Injection attacks.

You must give space to your concatenated strings.
"INSERT INTO CLIENT (Title,Fname,Sname)" + "[space here]VALUES (Mr,Joshua,Cameron-Mackintosh)"
however, it should look like this:
"INSERT INTO CLIENT (Title,Fname,Sname) VALUES (?,?,?)"
Always make use of parametrized queries. Please refer to:
http://blogs.technet.com/b/neilcar/archive/2008/05/21/sql-injection-mitigation-using-parameterized-queries.aspx

Why do I receive an incorrect syntax error when try to parameterize a table name?

I have the following code:
string strTruncateTable = "TRUNCATE TABLE #TableNameTruncate";
SqlCommand truncateTable = new SqlCommand(strTruncateTable, myConnection);
truncateTable.Parameters.AddWithValue("TableNameTruncate", tbTableName.Text);
truncateTable.ExecuteNonQuery();
Whenever I run the application, I get the following error:
Incorrect syntax near '#TableNameTruncate'
How can I fix the issue?

How can I fix the issue?
By specifying the table name as part of the SQL. Table and column names can't be parameterized in most database SQL dialects, including SQL Server.
You should either perform very stringent validation on the table name before putting it into the SQL, or have a whitelisted set of valid table names, in order to avoid SQL injection attacks in the normal way.

You can only parameterized your values, not your column names or table names no matter you use DML statements or DDL statements.
And by the way, parameters are supported for Data manipulation language operations not Data Manipulation language operations.
Data manipulation language =
SELECT ... FROM ... WHERE ...
INSERT INTO ... VALUES ...
UPDATE ... SET ... WHERE ...
DELETE FROM ... WHERE ...
TRUNCATE TABLE is a Data Definition Language statement. That's why you can't use TRUNCATE TABLE with parameters even only if you try to parameter a value. You need to specify it as a part of SQL query.
You might need to take a look at the term called Dynamic SQL

As mentioned by Jon Skeet, table name cannot be parametrized for truncate operation.
To fix this issue, fully qualified query needed to be written.
So you can put a conditional check by the parameter value #TableNameTruncate and using if or switch case statement create fully qualified query then execute it.
or simply
string strTruncateTable = "TRUNCATE TABLE " + TableNameTruncate.Value;
SqlCommand truncateTable = new SqlCommand(strTruncateTable, myConnection);
truncateTable.Parameters.AddWithValue("TableNameTruncate", tbTableName.Text);
truncateTable.ExecuteNonQuery();

C# prevent SQL injection for create statement

Does it make sense to prevent sql injection for a create statement? How could I do this?
I wanted to use command parameters, but it doesn't seam to work:
Example:
var createSql = "CREATE TABLE #TableName (#Column1 ...)";
var command = new SqlCommand();
command.CommandText = createSql;
command.Parameters.AddWithValue("#TableName", "XYZ");
command.Parameters.AddWithValue("#Column1", "Col");
// somewhere else
command.Connection = connection;
command.ExecuteNonReader(); // --> exception: invalid syntax at #TableName
Edit: The Column and TableNames are generated depending on other data. Indirectly also on userinput, yes. The given create statement is incomplete. It is just an example.
My problem is, that it seems that the command parameters are not replaced.

You cannot use bind variables for table or column names.
So you'll have to construct that SQL statement using string concatenation and if necessary, manual quoting/escaping, and be very careful how you go about it.
Direct user input would be very dangerous, but if it is only indirectly, for example just choosing options for auto-generated names, you should be okay.

in this specific code there can't be sql injection because the user doesn't have a say in this.
sql injection are caused when user input is either incorrectly filtered for string literal escape characters embedded in SQL statements or user input is not strongly typed and unexpectedly executed
in your case the user doesn't input anything so there is no worry.
however, your create table query is invalid. you can read here on create statement.
you can't use the "..." in a create statement, and every column must have a type

How do I protect this function from SQL injection?

public static bool TruncateTable(string dbAlias, string tableName)
{
string sqlStatement = string.Format("TRUNCATE TABLE {0}", tableName);
return ExecuteNonQuery(dbAlias, sqlStatement) > 0;
}

The most common recommendation to fight SQL injection is to use an SQL query parameter (several people on this thread have suggested it).
This is the wrong answer in this case. You can't use an SQL query parameter for a table name in a DDL statement.
SQL query parameters can be used only in place of a literal value in an SQL expression. This is standard in every implementation of SQL.
My recommendation for protecting against SQL injection when you have a table name is to validate the input string against a list of known table names.
You can get a list of valid table names from the INFORMATION_SCHEMA:
SELECT table_name
FROM INFORMATION_SCHEMA.Tables
WHERE table_type = 'BASE TABLE'
AND table_name = #tableName
Now you can pass your input variable to this query as an SQL parameter. If the query returns no rows, you know that the input is not valid to use as a table. If the query returns a row, it matched, so you have more assurance you can use it safely.
You could also validate the table name against a list of specific tables you define as okay for your app to truncate, as #John Buchanan suggests.
Even after validating that tableName exists as a table name in your RDBMS, I would also suggest delimiting the table name, just in case you use table names with spaces or special characters. In Microsoft SQL Server, the default identifier delimiters are square brackets:
string sqlStatement = string.Format("TRUNCATE TABLE [{0}]", tableName);
Now you're only at risk for SQL injection if tableName matches a real table, and you actually use square brackets in the names of your tables!

As far as I know, you can't use parameterized queries to perform DDL statements/ specify table names, at least not in Oracle or Sql Server. What I would do, if I had to have a crazy TruncateTable function, that had to be safe from sql injection would be to make a stored procedure that checks that the input is a table that is safe to truncate.
-- Sql Server specific!
CREATE TABLE TruncableTables (TableName varchar(50))
Insert into TruncableTables values ('MyTable')
go
CREATE PROCEDURE MyTrunc #tableName varchar(50)
AS
BEGIN
declare #IsValidTable int
declare #SqlString nvarchar(50)
select #IsValidTable = Count(*) from TruncableTables where TableName = #tableName
if #IsValidTable > 0
begin
select #SqlString = 'truncate table ' + #tableName
EXECUTE sp_executesql #SqlString
end
END

If you're allowing user-defined input to creep into this function via the tablename variable, I don't think SQL Injection is your only problem.
A better option would be to run this command via its own secure connection and give it no SELECT rights at all. All TRUNCATE needs to run is the ALTER TABLE permission. If you're on SQL 2005 upwards, you could also try using a stored procedure with EXECUTE AS inside.

CREATE OR REPLACE PROCEDURE truncate(ptbl_name IN VARCHAR2) IS
stmt VARCHAR2(100);
BEGIN
stmt := 'TRUNCATE TABLE '||DBMS_ASSERT.SIMPLE_SQL_NAME(ptbl_name);
dbms_output.put_line('<'||stmt||'>');
EXECUTE IMMEDIATE stmt;
END;

Use a stored procedure. Any decent db library (MS Enterprise Library is what I use) will handle escaping string parameters correctly.
Also, re:parameterized queries: I prefer to NOT have to redeploy my app to fix a db issue. Storing queries as literal strings in your source increases maintenance complexity.

Have a look at this link
Does this code prevent SQL injection?
Remove the unwanted from the tableName string.
I do not think you can use param query for a table name.

There are some other posts which will help with the SQL injection, so I'll upvote those, but another thing to consider is how you will be handling permissions for this. If you're granting users db+owner or db_ddladmin roles so that they can truncate tables then simply avoiding standard SQL injection attacks isn't sufficient. A hacker can send in other table names which might be valid, but which you wouldn't want truncated.
If you're giving ALTER TABLE permissions to the users on the specific tables that you will allow to be truncated then you're in a bit better shape, but it's still more than I like to allow in a normal environment.
Usually TRUNCATE TABLE isn't used in normal day-to-day application use. It's used for ETL scenarios or during database maintenance. The only situation where I might imagine it would be used in a front-facing application would be if you allowed users to load a table which is specific for that user for loading purposes, but even then I would probably use a different solution.
Of course, without knowing the specifics around why you're using it, I can't categorically say that you should redesign, but if I got a request for this as a DBA I'd be asking the developer a lot of questions.

Use parameterized queries.

In this concrete example you need protection from SQL injection only if table name comes from external source.
Why would you ever allow this to happen?
If you are allowing some external entity (end user, other system, what?)
to name a table to be dropped, why won't you just give them admin rights.
If you are creating and removing tables to provide some functionality for end user,
don't let them provide names for database objects directly.
Apart from SQL injection, you'll have problems with name clashes etc.
Instead generate real table names yourself (e.g DYNTABLE_00001, DYNTABLE_00002, ...) and keep a table that connects them to the names provided by user.
Some notes on generating dynamic SQL for DDL operations:
In most RDBMS-s you'll have to use dynamic SQL and insert table names as text.
Be extra careful.
Use quoted identifiers ([] in MS SQL Server, "" in all ANSI compliant RDBMS).
This will make avoiding errors caused by invalid names easier.
Do it in stored procedures and check if all referenced objects are valid.
Do not do anything irreversible. E.g. don't drop tables automatically.
You can flag them to be dropped and e-mail your DBA.
She'll drop them after the backup.
Avoid it if you can. If you can't, do what you can to minimize rights to other
(non-dynamic) tables that normal users will have.

You could use SQLParameter to pass in tableName value. As far as I know and tested, SQLParameter takes care of all parameter checking and thus disables possibility of injection.

If you can't use parameterized queries (and you should) ... a simple replace of all instances of ' with '' should work.
string sqlStatement = string.Format("TRUNCATE TABLE {0}", tableName.Replace("'", "''"));