c# MysqlDataReader return null (no replies)

Hello,

I trying to use sql command with MySqlDataReader and a string command.
This one work well with MysqlWorkbench, but in DotNet, I always have a null result.
My MySqlDataReader is null !!!

For some dark reasons, when my string command is : "SELECT * FROM table_medecin", my MySqlDatareader return all the records.
But when it is : "SELECT * FROM table_medecin WHERE Nom='xxx'", the return is NULL !!! But in MysqlWorkbench, I have the result...

I think that my sql syntax is good.

What's wrong ?

Thank you for your help...

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