You must specify 'resultType' or 'resultMap'.

This error message typically occurs when using MyBatis, a popular Java-based ORM framework, and indicates that the framework is unable to determine how to map the result of a SQL query to a Java object.

To resolve this error, you need to provide either a resultType or resultMap attribute in your MyBatis mapper XML file. The resultType attribute specifies the type of object that should be used to map the query result, while the resultMap attribute provides a mapping between the query result and a Java object.

For example, if you have a query that returns a list of User objects, you could specify the resultType attribute as follows:

<select id="getUserList" resultType="User">
    SELECT * FROM users
</select>

Alternatively, you could use a resultMap to specify a more complex mapping between the query result and a Java object:

<resultMap id="userMap" type="User">
    <id column="id" property="id"/>
    <result column="username" property="username"/>
    <result column="email" property="email"/>
</resultMap>

<select id="getUserList" resultMap="userMap">
    SELECT * FROM users
</select>

By providing either a resultType or resultMap attribute, you can help MyBatis correctly map the query result to a Java object and avoid the "must specify 'resultType' or 'resultMap'" error.