ASP.NET single quotes

When encountering error messages like "System.Data.SqlClient.SqlException: Incorrect syntax near..." or "Incorrect syntax near '..'. Unclosed quotation mark after the character string ')'", it indicates that there is a problem with the syntax of the SQL statement being executed, specifically related to the presence of single quotes.

System.Data.SqlClient.SqlException: Incorrect syntax near ... Incorrect syntax near '..'. Unclosed quotation mark after the character string ')'

The error occurs when attempting to insert data that includes a single quote character within an SQL statement. By default, single quotes are used to delimit string values in SQL. However, if the string itself contains a single quote, it can cause the SQL parser to misinterpret the statement and result in a syntax error.

Single quote character

To resolve this issue, one approach is to escape the single quote character by replacing it with two single quotes. This effectively treats the second single quote as a literal character and avoids confusing the SQL parser. For example, if you want to insert the string "net-informations's", you would replace the single quote with two single quotes: "net-informations''s".

insert into tablename (field1) values('net-informations''s')

By employing this means, the SQL statement will be constructed properly, thus eliminating syntax errors that only occur with the single quotes within the data. It does this by making the program understand that the single quote is used to acknowledge the string value part of the language instead of being a delimiter.

For avoiding each time adding another single quote to the string , here we implement a function to replace the string with two single quotes.

Public Function convertQuotes(ByVal str As String) As String convertQuotes = str.Replace("'", "''") End Function
public string convertQuotes(string str) { return str.Replace("'", "''"); }

From the following program you can see how to handle single quotes in ASP.Net applications.


<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" ""> <html xmlns=""> <head id="Head1" runat="server"> <title>Untitled Page</title> </head> <body> <form id="form1" runat="server"> <div> <asp:Button ID="Button1" runat="server" Text="Button" onclick="Button1_Click" /> <br /> <asp:Label ID="Label1" runat="server" Text="Label"></asp:Label> </div> </form> </body> </html>
Full Source | C#
using System; using System.Data ; using System.Data.SqlClient ; using System.Configuration; public partial class _Default : System.Web.UI.Page { protected void Button1_Click(object sender, EventArgs e) { string connectionString = ConfigurationManager.ConnectionStrings["SQLDbConnection"].ToString(); SqlConnection connection = new SqlConnection(connectionString); SqlDataAdapter adapter = new SqlDataAdapter(); string sql = null; string field1 = "'s"; string field2 = "C#"; sql = "insert into newtest (field1,field2) values('" + convertQuotes(field1) + "','" + convertQuotes(field2) + "')"; try { connection.Open(); adapter.InsertCommand = new SqlCommand(sql, connection); adapter.InsertCommand.ExecuteNonQuery(); Label1.Text = "Row inserted !! "; } catch (Exception ex) { Label1.Text = "Error in execution " + ex.ToString(); } } //here is the function to handle single quoted characters public string convertQuotes(string str) { return str.Replace("'", "''"); } }
Full Source | VB.NET
Imports System.Data Imports System.Data.SqlClient Imports System.Configuration Partial Class _Default Inherits System.Web.UI.Page Protected Sub Button1_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles Button1.Click Dim connectionString As String Dim connection As SqlConnection connectionString = ConfigurationManager.ConnectionStrings("SQLDbConnection").ToString connection = New SqlConnection(connectionString) Dim adapter As New SqlDataAdapter Dim sql As String Dim field1 As String = "'s" Dim field2 As String = "VB.NET" sql = "insert into tablename (field1,field2) values('" & convertQuotes(field1) & "','" & convertQuotes(field2) & "')" Try connection.Open() adapter.InsertCommand = New SqlCommand(sql, connection) adapter.InsertCommand.ExecuteNonQuery() Label1.Text = "Row inserted !! " Catch ex As Exception Label1.Text = "Error in execution " & ex.ToString End Try End Sub 'here is the function to handle single quoted characters Public Function convertQuotes(ByVal str As String) As String convertQuotes = str.Replace("'", "''") End Function End Class


It's important to note that handling special characters and escaping in SQL statements is crucial to prevent potential SQL injection vulnerabilities. In addition to replacing single quotes, it is recommended to use parameterized queries or prepared statements to securely pass data to SQL statements, mitigating the risk of malicious input.