数据库工具类

public interface DbMapper {

    /**
     * 查询数据库类型
     */
    String queryDbType();
}
 <select id="queryDbType" resultType="java.lang.String">
        select
        <choose>
            <when test="_databaseId == 'mysql'">
                'mysql'
            </when>
            <when test="_databaseId == 'oracle'">
                'oracle'
            </when>
            <when test="_databaseId == 'sqlserver'">
                'sqlserver'
            </when>
            <when test="_databaseId == 'db2'">
                'db2'
            </when>
            <when test="_databaseId == 'postgresql'">
                'postgresql'
            </when>
            <when test="_databaseId == 'dm'">
                'dm'
            </when>
            <otherwise>
                'unknown'
            </otherwise>
        </choose> as dbType
    </select>