其中”UNION“为合并两条查询语句，注意，查询结果中相同的列数据类型必须一致。
SELECT
ID,
CONTENT,
CREATE_DATE,
@rownum0 AS TYPE
FROM
(SELECT @rownum0 := 0) r,
`message_reply`
WHERE
USER_ID = #{userId,jdbcType=INTEGER}
UNION
SELECT
ID,
KEY_WORD AS CONTENT,
CREATE_DATE,
@rownum1 AS TYPE
FROM
(SELECT @rownum1 := 1) b,
`message`
WHERE
USER_ID = #{userId,jdbcType=INTEGER}
ORDER BY
CREATE_DATE DESC;