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How to drop SQL table from C# without opening to code injection? [duplicate]

This question already has answers here:
Sanitize table/column name in Dynamic SQL in .NET? (Prevent SQL injection attacks)
(3 answers)
Closed 5 months ago.
Edit: I marked that the linked question was useful, but I didn't intend to mean that it completely answered my question here, which after reviewing others' comments and answers here, I realize I need two different escaped versions of table, one as a safe single-quoted identifier, and one as a safe single-bracketed identifier.
I need to drop a SQL server table from C# with the table name as a parameter.
This is my code:
private static void DropSqlTableIfExists(string connectionString, string table)
{
string query = "if object_id (#table, 'U') is not null begin drop table #table; end";
using SqlConnection conn = new(connectionString);
using SqlCommand command = new(query, conn);
command.Parameters.AddWithValue("#table", table);
conn.Open();
command.ExecuteNonQuery();
}
The above code gives me an error, Incorrect syntax near '#table'.
I could of course put the table name directly into the query string, but that would allow code injection, which I need to avoid.
What is the best way to go about this?
EDIT 2:
Based on feedback, I updated the code to look like this:
private static void DropSqlTableIfExists(string connectionString, string table)
{
string tableSafeQuoted = $"'{table.Replace("'", "''")}'";
string tableSafeBracketed = $"[{table.Replace("]", "]]").Replace(".", "].[")}]";
string query = $"if object_id ({tableSafeQuoted}, 'U') is not null begin drop table {tableSafeBracketed}; end";
using SqlConnection conn = new(connectionString);
using SqlCommand command = new(query, conn);
conn.Open();
command.ExecuteNonQuery();
}
tbh, I'm not sure if it's 100% safe, due to the oddity of the . replacement.. but I think unless someone gives me a good reason not to, I will leave it like this..

You'll need to escape/encode the table name as an identifier. In SQL Server, this is typically done by replacing any closing brackets (]) in the name with two consecutive brackets (]]), and then surrounding the result with brackets ([...]).
You can either write a simple method to do this yourself, or take on a dependency like ScriptDom, which allows you to do this:
var escapedTableName = Identifier.EncodeIdentifier(tableName);
If your SQL Server database is set to use double-quoted identifiers, do something similar, but with double-quotes instead of brackets. Or, with ScriptDom:
var escapedTableName = Identifier.EncodeIdentifier(tableName, QuoteType.DoubleQuote);
Note that encoding the table name makes any .s act as if they're part of the table name itself. If your table name is supposed to have qualifiers (database, schema), each of those must be escaped individually, so you'll probably want to have them passed in as a separate argument, or create a separate type to represent the combination of these names.

There is probably a more elegant way to do this, but here's one possible way:
declare #dynamicsql nvarchar(max)
set #dynamicsql = 'DROP TABLE dbo.' + QUOTENAME(#table) + '';
if object_id (#table, 'U') is not null
begin
EXEC sp_executesql #dynamicsql;
end
so in your specific case it will be:
private static void DropSqlTableIfExists(string connectionString, string table)
{
string query = #"
declare #dynamicsql nvarchar(max)
set #dynamicsql = 'DROP TABLE dbo.' + QUOTENAME(#table) + '';
if object_id (#table, 'U') is not null
begin
EXEC sp_executesql #dynamicsql;
end
";
using SqlConnection conn = new(connectionString);
using SqlCommand command = new(query, conn);
command.Parameters.AddWithValue("#table", table);
conn.Open();
command.ExecuteNonQuery();
}
I hope it helps!

Must declare table variable error with c# paramaterized query

I am getting an error with an SQL statement:
must declare the table variable #table
I don't know how I should fix it. Here is the code for the part that makes the query (for example 3 is Communications, 4 is Radio:basic, 5 is 45, 6 is 5, and 7 is 0).
string table = "Skills" + info[3];
SqlCommand cmd = new SqlCommand("use palladium; insert into #category(skill, basepercent, lvlpercent, special) values ( #skillname , #base , #lvl , #special);");
cmd.Parameters.AddWithValue("#category", table);
cmd.Parameters.AddWithValue("#skillname", info[4]);
cmd.Parameters.AddWithValue("#base", info[5]);
cmd.Parameters.AddWithValue("#lvl", info[6]);
cmd.Parameters.AddWithValue("#special", info[7]);
general.dbsend(cmd, connection);

You can't have a table name as a variable in a static query. You can in a dynamic query, by formatting the table name in the query rather than supplying it as a parameter.
SqlCommand cmd = new SqlCommand("use palladium; insert into ["+table.Replace("]","]]")+"](skill, basepercent, lvlpercent, special) values ( #skillname , #base , #lvl , #special);");
The replace bit guards against SQL Injection.

Store multiple values from SELECT statement and then insert into different table

I want to use a SELECT statement into a table based on multiple values from ListBox and get multiple IDs and then run an INSERT statement and store the multiple IDs into a different table from INSERT statement.
My code below is not working as I am getting "NULL" in single row instead of multiple IDs in multiple rows.
I am using a stored procedure for all the SQL statements.
Please see my code below:
Code-behind of my ASPX web page:
string listboxvalue = "";
foreach (ListItem item in listbox.Items)
{
if (item.Selected)
{
listboxvalue += item.Text + ',';
}
}
listboxvalue = listboxvalue.Substring(0, listboxvalue.Length - 1);
cmd.Parameters.AddWithValue("spselectvalue", listboxvalue);
Stored procedure:
#spselectvalue nvarchar(MAX),
// Select multiple Ids based on multiple items from list box
DECLARE #Dis TABLE (DisID int)
INSERT INTO #Dis
SELECT DId
FROM [table name]
WHERE [COLUMN] IN ('+#spselectvalue +')
EXEC sp_executesql #Dis
// Insert multiple Ids (from above select statement) into different table
INSERT INTO [dbo].[DifferentTable] ([SelectedIds])
VALUES
(
(SELECT DisID from #Dis)
)

Seems like your problem is that you don't know how to get a list of ID's into a stored procedure for processing. Hopefully this example will help. If you do it this way, you won't have to mess with comma-delimited strings or dynamic SQL.
First, define a SQL type that can contain your list of IDs:
CREATE TYPE dbo.MyList
AS TABLE
(
ID VarChar(50)
);
Then, write a stored procedure that accepts this type as its input parameter:
CREATE PROCEDURE dbo.InsertAList
#List AS dbo.MyList READONLY
AS
BEGIN
SET NOCOUNT ON;
INSERT INTO [dbo].[DifferentTable]
SELECT ID FROM #List
END
Now to bind your data to the stored procedure from the c# end. To bind it, you have to store the data in a DataTable first, which is relatively easy:
var table = new DataTable();
table.Columns.Add("ID", typeof(string));
foreach (ListItem item in listBox.Items.Where(i => i.Selected))
{
table.Rows.Add(item.Text);
}
Then submit the table to the stored procedure like so:
var cmd = new SqlCommand()
{
CommandType = CommandType.StoredProcedure,
CommandText = "InsertAList",
Connection = myConnection
};
cmd.Parameters.Add(new SqlParameter("#List", SqlDbType.Structured)
{
TypeName = "dbo.MyList",
Value = table
});
cmd.ExecuteNonQuery();

That doesn't seem like a valid (or logical) SQL. The exec sp_executesql #Dis shouldn't be there or #Dis shouldn't be a table.
When using sp_executesql the parameter should be a string containing the statement to execute (documentation).
Detailed answer can be found here.
Also: the INSERT INTO #Dis ... line won't work as you expect when written that way, for the reasons mentioned in the linked question (and Erland Sommarskog blog mentioned there).

Selected values considered as numeric.
DECLARE #Sqltext nvarchar(max) =
'INSERT INTO [dbo].[DifferentTable] ([SelectedIds])
SELECT DId
FROM [table name]
WHERE [COLUMN] IN (' + #spselectvalue + ')'
EXEC sp_executesql #Sqltext

A better way to achieve INSERT without hitting the database multiple times

I have the following, I could make it work as I want to but I think i'm doing it the wrong way, could you please explain how this could be done in a more efficient way ? While also looping on Categories and doing the same as with Districts within the same Insert() Method.
Thanks in advance.
#region Methods
public int Insert(List<District> Districts, List<Category> Categories)
{
StringBuilder sqlString = new StringBuilder("INSERT INTO Stores (name, image) VALUES (#Name, #Image);");
using (SqlConnection sqlConnection = new
SqlConnection(ConfigurationManager.ConnectionStrings["OahuDB"].ConnectionString))
{
SqlCommand sqlCommand = new SqlCommand(sqlString.ToString(), sqlConnection);
sqlCommand.Parameters.AddWithValue("#Name", this.Name);
sqlCommand.Parameters.AddWithValue("#Image", this.Image);
sqlConnection.Open();
int x = (int)sqlCommand.ExecuteScalar();
sqlString.Clear();
sqlCommand.Parameters.Clear();
foreach (District item in Districts)
{
sqlString.AppendLine("INSERT INTO districts_has_stores (district_id, store_id) VALUES (#DistrictID, #StoreID);");
sqlCommand.CommandText = sqlString.ToString();
sqlCommand.Parameters.AddWithValue("#DistrictID", item.ID);
sqlCommand.ExecuteNonQuery();
}
return x;
}
}
EDIT
Is is wrong to achieve the above by doing the following ?
sqlString.Clear();
sqlCommand.Parameters.Clear();
sqlString.AppendLine("INSERT INTO districts_has_stores (district_id, store_id) VALUES (#DistrictID, #StoreID);");
sqlCommand.CommandText = sqlString.ToString();
sqlCommand.Parameters.AddWithValue("#StoreID", x);
foreach (District item in Districts)
{
sqlCommand.Parameters.AddWithValue("#DistrictID", item.ID);
sqlCommand.ExecuteNonQuery();
}
sqlString.Clear();
sqlCommand.Parameters.Clear();
sqlString.AppendLine("INSERT INTO categories_has_stores (category_id, store_id) VALUES (#CategoryID, #StoreID);");
sqlCommand.CommandText = sqlString.ToString();
sqlCommand.Parameters.AddWithValue("#StoreID", x);
foreach (Category item in Categories)
{
sqlCommand.Parameters.AddWithValue("#CategoryID", item.ID);
sqlCommand.ExecuteNonQuery();
}

The first obvious thing is to move the invariant part of the sqlCommand out of the loop
sqlCommand.Parameters.Clear();
sqlString.Clear();
sqlString.AppendLine("INSERT INTO districts_has_stores (district_id, store_id) VALUES (#DistrictID, #StoreID);");
sqlCommand.CommandText = sqlString.ToString();
sqlCommand.Parameters.AddWithValue("#DistrictID", 0); // as dummy value
sqlCommand.Parameters.AddWithValue("#StoreID", x); // invariant
foreach (District item in Districts)
{
sqlCommand.Parameters["#DistrictID"].Value = item.ID;
sqlCommand.ExecuteNonQuery();
}
But this doesn't answer your fundamental problem. How to avoid hitting the database multiple times.
You could build a query with multiple inserts like this
sqlString.Clear();
sqlString.Append("INSERT INTO districts_has_stores (district_id, store_id) VALUES (");
foreach(District item in Districts)
{
sqlString.Append(item.ID.ToString);
sqlString.Append(", ")
sqlString.Append(x.ToString());
sqlString.Append("),");
}
sqlString.Length--;
sqlCommand.CommandText = sqlString.ToString()
But string concatenation is really a bad practice and I present this solution just as an example and I don't want to suggest this kind of approach.
The last possibility are Table-Valued Parameters (Only from SqlServer 2008).
First you need to create a Sql Type for the table you will pass in
CREATE TYPE dbo.DistrictsType AS TABLE
( DistrictID int, StoreID int )
and a StoredProcedure that will insert the data from the datatable passed in
CREATE PROCEDURE usp_InsertDistricts
(#tvpNewDistricts dbo.DistrictsType READONLY)
AS
BEGIN
INSERT INTO dbo.Districts (DistrictID, StoreID)
SELECT dt.DistrictID, dt.StoreID FROM #tvpNewDistricts AS dt;
END
then, back to your code you pass the district into the storedprocedure
(Probably you need to convert your List in a DataTable)
DataTable dtDistricts = ConvertListToDataTable(Districts);
SqlCommand insertCommand = new SqlCommand("usp_InsertDistricts", sqlConnection);
SqlParameter p1 = insertCommand.Parameters.AddWithValue("#tvpNewDistricts", dtDistricts);
p1.SqlDbType = SqlDbType.Structured;
p1.TypeName = "dbo.DistrictsType";
insertCommand.ExecuteNonQuery();
Well, if you look back at the link above, you will find other ways to pass your data in a single step to the database backend.... (Scroll to the end and you will find also a method that doesn't require a stored procedure on the database)

Assuming Stores has an identity column, in SQL Server, create a table type and a table-valued parameter to take advantage of it:
CREATE TYPE dbo.DistrictsTVP AS TABLE
(
DistrictID INT -- PRIMARY KEY? I hope so.
);
GO
CREATE PROCEDURE dbo.InsertStoreAndDistricts
#Name NVARCHAR(255),
#Image <some data type???>,
#Districts dbo.DistrictsTVP READONLY
AS
BEGIN
SET NOCOUNT ON;
DECLARE #StoreID INT;
INSERT dbo.Stores(name, [image]) SELECT #Name, #Image;
SET #StoreID = SCOPE_IDENTITY();
INSERT dbo.district_has_stores(district_id, store_id)
SELECT DistrictID, #StoreID
FROM #Districts;
END
GO
Then in C#, you can pass your List in directly without any looping:
using (...)
{
SqlCommand cmd = new SqlCommand("dbo.InsertStoreAndDistricts", sqlConnection);
cmd.CommandType = CommandType.StoredProcedure;
SqlParameter tvparam = cmd.Parameters.AddWithValue("#Districts", Districts);
tvparam.SqlDbType    = SqlDbType.Structured;
// other params here - name and image
cmd.ExecuteNonQuery();
}

Recently in my project i used XML as a data type in my stored proc and did insert update and delete in just one shot instead of hitting the database multiple times .
Sample Stored proc
ALTER PROCEDURE [dbo].[insertStore]
#XMLDATA xml,
#name varchar(50),
#image datatype
AS
Begin
INSERT INTO Store
(name
,image
)
Select XMLDATA.item.value('#name[1]', 'varchar(10)') AS Name,
XMLDATA.item.value('#image[1]', 'yourData type') AS Image
FROM #XMLDATA.nodes('//Stores/InsertList/Store') AS XMLDATA(item)
END
Similarly you can write for update and delete .In C# u need to create the xml
public string GenerateXML(List<District> Districts)
var xml = new StringBuilder();
var insertxml = new StringBuilder();
xml.Append("<Stores>");
for (var i = 0; i < Districts.Count; i++)
{ var obj = Districts[i];
insertxml.Append("<Store");
insertxml.Append(" Name=\"" + obj.Name + "\" ");
insertxml.Append(" Image=\"" + obj.Image + "\" ");
insertxml.Append(" />");
}
xml.Append("<InsertList>");
xml.Append(insertxml.ToString());
xml.Append("</InsertList>");
SqlCommand cmd= new SqlCommand("insertStore",connectionString);
cmd.CommandType=CommandType.StoredProcedure;
SqlParameter param = new SqlParameter ();
param.ParameterName ="#XMLData";
param.value=xml;
paramter.Add(param);
cmd.ExecuteNonQuery();

Personally, I would create a stored procedure for the insert and pass in a Table-Valued param, which would allow you to do
INSERT tbl (f1, f2, ... fN)
SELECT * FROM #TVP
http://msdn.microsoft.com/en-us/library/bb510489.aspx
Unless you're using SQL 2005, then I would use an XML param in my stored proc and Serialize a collection to be inserted.

Think about your system design. Where is the data that you need to insert coming from? If it's already in the database, or another database, or some other kind of data store, you should be able to achieve a more bulk kind of transfer, simply inserting from one database to the other in a loop in stored procedure.
If the data is coming from a user, or some incompatible data store, like say an export from some third party program, then you basically have to realize that to get it into the database will involve quite of few round-trips to the database. You can use some tables, or XML or such , but those are actually closer to doing a bulk insert using other methods.
The bottom line is that SQL databases are designed to do inserts one at a time. This is 99% of the time OK because you are never asking users using the UI to type in thousands of things at one time.

String list in SqlCommand through Parameters in C#

Working with a SqlCommand in C# I've created a query that contains a IN (list...) part in the where clause. Instead of looping through my string list generating the list I need for the query (dangerous if you think in sqlInjection). I thought that I could create a parameter like:
SELECT blahblahblah WHERE blahblahblah IN #LISTOFWORDS
Then in the code I try to add a parameter like this:
DataTable dt = new DataTable();
dt.Columns.Add("word", typeof(string));
foreach (String word in listOfWords)
{
dt.Rows.Add(word);
}
comm.Parameters.Add("LISTOFWORDS", System.Data.SqlDbType.Structured).Value = dt;
But this doesn't work.
Questions:
Am I trying something impossible?
Did I took the wrong approach?
Do I have mistakes in this approach?
Thanks for your time :)

What you are trying to do is possible but not using your current approach. This is a very common problem with all possible solutions prior to SQL Server 2008 having trade offs related to performance, security and memory usage.
This link shows some approaches for SQL Server 2000/2005
SQL Server 2008 supports passing a table value parameter.
I hope this helps.

You want to think about where that list comes from. Generally that information is in the database somewhere. For example, instead of this:
SELECT * FROM [Table] WHERE ID IN (1,2,3)
You could use a subquery like this:
SELECT * FROM [Table] WHERE ID IN ( SELECT TableID FROM [OtherTable] WHERE OtherTableID= #OtherTableID )

If I understand right, you're trying to pass a list as a SQL parameter.
Some folks have attempted this before with limited success:
Passing Arrays to Stored Procedures
Arrays and Lists in SQL 2005
Passing Array of Values to SQL Server without String Manipulation
Using MS SQL 2005's XML capabilities to pass a list of values to a command

Am I trying something impossible?
No, it isn't impossible.
Did I took the wrong approach?
Your approach is not working (at least in .net 2)
Do I have mistakes in this approach?
I would try "Joel Coehoorn" solution (2nd answers) if it is possible.
Otherwise, another option is to send a "string" parameter with all values delimited by an separator. Write a dynamic query (build it based on values from string) and execute it using "exec".
Another solution will be o build the query directly from code. Somthing like this:
StringBuilder sb = new StringBuilder();
for (int i=0; i< listOfWords.Count; i++)
{
sb.AppendFormat("p{0},",i);
comm.Parameters.AddWithValue("p"+i.ToString(), listOfWords[i]);
}
comm.CommandText = string.Format(""SELECT blahblahblah WHERE blahblahblah IN ({0})",
sb.ToString().TrimEnd(','));
The command should look like:
SELECT blah WHERE blah IN (p0,p1,p2,p3...)...p0='aaa',p1='bbb'
In MsSql2005, "IN" is working only with 256 values.

I would recommend setting the parameter as a comma delimited string of values and use a Split function in SQL to turn that into a single column table of values and then you can use the IN feature.
http://www.sqlteam.com/forums/topic.asp?TOPIC_ID=50648 - Split Functions

If you want to pass the list as a string in a parameter, you could just build the query dynamically.
DECLARE #query varchar(500)
SET #query = 'SELECT blah blah WHERE blahblah in (' + #list + ')'
EXECUTE(#query)

I used to have the same problem, I think there is now way to do this directly over the ADO.NET API.
You might consider inserting the words into a temptable (plus a queryid or something) and then refering to that temptable from the query. Or dynamically creating the query string and avoid sql injection by other measures (e.g. regex checks).

This is an old question but I've come up with an elegant solution for this that I love to reuse and I think everyone else will find it useful.
First of all you need to create a FUNCTION in SqlServer that takes a delimited input and returns a table with the items split into records.
Here is the following code for this:
ALTER FUNCTION [dbo].[Split]
(
#RowData nvarchar(max),
#SplitOn nvarchar(5) = ','
)
RETURNS #RtnValue table
(
Id int identity(1,1),
Data nvarchar(100)
)
AS
BEGIN
Declare #Cnt int
Set #Cnt = 1
While (Charindex(#SplitOn,#RowData)>0)
Begin
Insert Into #RtnValue (data)
Select
Data = ltrim(rtrim(Substring(#RowData,1,Charindex(#SplitOn,#RowData)-1)))
Set #RowData = Substring(#RowData,Charindex(#SplitOn,#RowData)+1,len(#RowData))
Set #Cnt = #Cnt + 1
End
Insert Into #RtnValue (data)
Select Data = ltrim(rtrim(#RowData))
Return
END
You can now do something like this:
Select Id, Data from dbo.Split('123,234,345,456',',')
And fear not, this can't be susceptible to Sql injection attacks.
Next write a stored procedure that takes your comma delimited data and then you can write a sql statement that uses this Split function:
CREATE PROCEDURE [dbo].[findDuplicates]
#ids nvarchar(max)
as
begin
select ID
from SomeTable with (nolock)
where ID in (select Data from dbo.Split(#ids,','))
end
Now you can write a C# wrapper around it:
public void SomeFunction(List<int> ids)
{
var idsAsDelimitedString = string.Join(",", ids.Select(id => id.ToString()).ToArray());
// ... or however you make your connection
var con = GetConnection();
try
{
con.Open();
var cmd = new SqlCommand("findDuplicates", con);
cmd.Parameters.Add(new SqlParameter("#ids", idsAsDelimitedString));
var reader = cmd.ExecuteReader();
// .... do something here.
}
catch (Exception)
{
// catch an exception?
}
finally
{
con.Close();
}
}