Question

在这里，我尝试内部加入SEARCHED_TAGS表和USER表。在这里，我使用三次相同的连接。不仅如此，我多次使用此查询。这会导致查询速度变慢吗？我怎么能一次写这个查询而不是3次。

您可以在下面看到查询。

(
 select st.SEARCH_TEXT as SEARCH_TEXT
 from SEARCHED_TAGS st
 inner join USER usr
 on st.SEARCH_BY=usr.USER_ID
 where (st.SEARCH_TEXT like :tagText) and (st.SEARCH_BY = :userId) and (usr.DEP_ID = :userDep)
 order by st.SEARCH_TIME desc
 limit 2
)
UNION
(
 select st.SEARCH_TEXT as SEARCH_TEXT
 from SEARCHED_TAGS st
 inner join USER usr
 on st.SEARCH_BY = usr.USER_ID
 where (st.SEARCH_TEXT like :tagText) and not (st.SEARCH_BY = :userId) and (usr.DEP_ID = :userDep)
 order by st.SEARCH_TIME desc
 limit 2
)
UNION
(
 select st.SEARCH_TEXT as SEARCH_TEXT
 from SEARCHED_TAGS st
 inner join USER usr
 on st.SEARCH_BY= usr.USER_ID
 where (st.SEARCH_TEXT like :tagText) and not (st.SEARCH_BY = :userId) and not (usr.DEP_ID = :userDep)
 order by st.SEARCH_TIME desc
 limit 2
)

我可以这样写而不是上面。

inner join USER usr
on st.SEARCH_BY=usr.USER_ID
(
 select st.SEARCH_TEXT as SEARCH_TEXT
 from SEARCHED_TAGS st
 where (st.SEARCH_TEXT like :tagText) and (st.SEARCH_BY = :userId) and (usr.DEP_ID = :userDep)
 order by st.SEARCH_TIME desc
 limit 2
)
UNION
(
 select st.SEARCH_TEXT as SEARCH_TEXT
 from SEARCHED_TAGS st
 where (st.SEARCH_TEXT like :tagText) and not (st.SEARCH_BY = :userId) and (usr.DEP_ID = :userDep)
 order by st.SEARCH_TIME desc
 limit 2
)
UNION
(
 select st.SEARCH_TEXT as SEARCH_TEXT
 from SEARCHED_TAGS st
 where (st.SEARCH_TEXT like :tagText) and not (st.SEARCH_BY = :userId) and not (usr.DEP_ID = :userDep)
 order by st.SEARCH_TIME desc
 limit 2
)

谢谢..

Answer 1

由于限制语句，这可能是普通MySQL可以做到的最好的。但是使用会话变量我们可以做得更好：

SELECT SEARCH_TEXT
FROM
(
    SELECT SEARCH_TEXT, grp,
        (@num:=if(@group = grp, @num +1, if(@group := grp, 1, 1))) row_number
    FROM
    (
        SELECT
            st.SEARCH_TEXT as SEARCH_TEXT,
            st.SEARCH_TIME,
            CASE WHEN (st.SEARCH_TEXT like :tagText) AND (st.SEARCH_BY = :userId) AND
                      (usr.DEP_ID = :userDep) THEN 1
                 WHEN (st.SEARCH_TEXT like :tagText) AND NOT (st.SEARCH_BY = :userId) AND
                      (usr.DEP_ID = :userDep) THEN 2
                 WHEN (st.SEARCH_TEXT like :tagText) AND NOT (st.SEARCH_BY = :userId) AND NOT
                      (usr.DEP_ID = :userDep) THEN 3
                 ELSE 4 END AS grp
        FROM SEARCHED_TAGS st
        INNER JOIN USER usr
            ON st.SEARCH_BY = usr.USER_ID
    ) t1
    CROSS JOIN (select @num:=0, @group:=null) t2
    ORDER BY grp, t1.SEARCH_TIME DESC
) t
WHERE
    t.row_number <= 2 AND
    t.grp <= 3;

此代码未经测试，主要是因为您的查询过于复杂而无法轻松进行测试，但如果遇到任何问题，我可以与您进行迭代。

如何添加一个内连接而不是3个内连接

1 个答案: