mysql - 操作数应在 java 中包含 1 列

Question

String  sql = "SELECT (Employee_name, Password) FROM employee WHERE (Employee_name = '"+name+"'  AND Password = '"+password+"')";

并在 JSP java.sql.sqlexception 中获取以下异常插入操作数应包含 1 列

请帮忙。

Answer 1

正确的方法是

String  sql = "SELECT Employee_name, Password FROM employee WHERE Employee_name = '"+name+"'  AND Password = '"+password+"'";

您可以保留()for where 子句，但不能保留在选择列表中。这就是您的情况

mysql> select (firstname,email) from users limit 1 ;
ERROR 1241 (21000): Operand should contain 1 column(s)

Answer 2

删除括号，它会工作。

String  sql = "SELECT Employee_name, Password 
           FROM employee WHERE Employee_name = '"+name+"'  
                      AND Password = '"+password+"'";

通常，当我们需要添加嵌套查询和组合条件时，我们会使用括号。如果为列名添加括号，Mysql 将其识别为单列。这就是错误按原样出现的原因。

Answer 3

您的查询必须是这样的：

String  sql = "SELECT Employee_name, Password 
                  FROM employee 
                   WHERE (Employee_name = '"+name+"'  
                     AND Password = '"+password+"')";