c# - MySQL 使用 OR 运算符选择

Question

在 C# 桌面应用程序中，我使用MySqlConnection MySqlCommand cmd.CommandText：

"select * from reg where username='" + user + "' and password='" + pass + "' and key='" + key + "'";

选择记录，但我想弄清楚OR，如果我想user OR email从单个输入（如string UserOrEmail = textBox1.Text.Trim();.

看起来条件适用于username=or email=，但在这种情况下，以下值检查不起作用，似乎我必须在这里使用一些正确的方法：

"select * from reg where username='" + UserOrEmail + "' or email='" + UserOrEmail + "' and password='" + pass + "' and key='" + key + "'";

Answer 1

您需要括号，因为运算符AND的优先级高于OR：

"select * from reg where (username='" + UserOrEmail + "' or email='" + UserOrEmail + "') and password='" + pass + "' and key='" + key + "'";

或使用运算符IN：

"select * from reg where '" + UserOrEmail + "' in (username, email) and password='" + pass + "' and key='" + key + "'";