MySQL：System.Data.Entity ，MySqlCommand, MySqlParameter and "LIKE" %

Introduction

Using GetSqlStringCommand with a text comparative, with LIKE, in ADO.NET and the MySQLParamenter gets you different result between executing by hand the command in a MySQL client and executing it through ADO.NET.

Background

This occurs when you write a command like this "SELECT * FROM users WHERE name LIKE '%John%'", this will return:

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John Frank
Johnny Philips
H. F. John

But for ADO.NET if you set a var, like "@name" and update the command like this "SELECT * FROM users WHERE name LIKE '%@name%'", ADO.NET treats it as the string '@name' you will return 0 result, because no exists any user with the name @name or the email @name, but yes someone with an email of the domain "name.com", like [e-mail], but this is a casualty and not, what we expect.

So you need to remove the simple quota and set the value appending and preceding with "%".

Using the code

//错误写法
MySQLCommand cmd = oldDb.GetSqlStringCommand(CommandType.Text,"SELECT * FROM users WHERE name LIKE '%@name%'");
MySQLParameter nameParameter= cmd.CreateParameter();
nameParameter.DbType = DbType.String;
nameParameter.ParameterName = "@name";
nameParameter.Value = "John";

//正确写法
MySQLCommand cmd = oldDb.GetSqlStringCommand(CommandType.Text,"SELECT * FROM users WHERE name LIKE @name");
MySQLParameter nameParameter= cmd.CreateParameter();
nameParameter.DbType = DbType.String;
nameParameter.ParameterName = "@searchText"
nameParameter.Value = "%John%"; 

补充说明：即使在变量值前后，加上百分比%