Why Does My MySQL Query Work in phpMyAdmin but Fail in .NET, and How Can I Fix It?

How to Utilize MySQL User Defined Variables in .NET MySqlCommand

Issue

Users encounter difficulties executing a query in .NET using MySqlAdapter that successfully runs in phpMyAdmin due to the inclusion of @rownum. This system variable is mistaken for a parameter and raises an exception since it's not defined.

Solution

To resolve this issue, follow these steps:

1. Update Connection String: Add ";Allow User Variables=True" to the connection string.
2. Handle Results Discrepancy: Note that the result counting in .NET may differ from phpMyAdmin. In .NET, the counting starts from 0, while phpMyAdmin starts from 1.

Example

using (var sqlConnection = new MySqlConnection(SOURCE_CONNECTION + ";Allow User Variables=True"))
{
    sqlConnection.Open();

    MySqlDataAdapter sqlAdapter = new MySqlDataAdapter(SqlStatement, sqlConnection);

    DataTable table = new DataTable();
    sqlAdapter.Fill(table);
    sqlConnection.Close();

    return table;
}

Additional Tips

For alternative methods of obtaining line numbers, consider the following options:

• Add a Row ID Column: Add a column to the database table to store sequential IDs.
• Use a temp table: Create a temporary table that includes a row number column and join it to your original table.
• Utilize a helper method: Write a custom helper method that generates line numbers based on the row data.

The above is the detailed content of Why Does My MySQL Query Work in phpMyAdmin but Fail in .NET, and How Can I Fix It?. For more information, please follow other related articles on the PHP Chinese website!