如何对多个表使用mysql group by和inner join限制记录数

你可以用 GROUP_CONCAT 聚合函数,将所有年份归为一列,按 id 并由 rate :

SELECT   id, GROUP_CONCAT(year ORDER BY rate DESC) grouped_year
FROM     yourtable
GROUP BY id

结果:

-----------------------------------------------------------
|  ID | GROUPED_YEAR                                      |
-----------------------------------------------------------
| p01 | 2006,2003,2008,2001,2007,2009,2002,2004,2005,2000 |
| p02 | 2001,2004,2002,2003,2000,2006,2007                |
-----------------------------------------------------------

然后你可以用 FIND_IN_SET ,它返回第一个参数在第二个参数中的位置。

SELECT FIND_IN_SET('2006', '2006,2003,2008,2001,2007,2009,2002,2004,2005,2000');
1

SELECT FIND_IN_SET('2009', '2006,2003,2008,2001,2007,2009,2002,2004,2005,2000');
6

结合使用 GROUP_CONCAT 和 FIND_IN_SET ,并按find_in_set返回的位置进行筛选,然后可以使用此查询仅返回每个id的前5年:

SELECT
  yourtable.*
FROM
  yourtable INNER JOIN (
    SELECT
      id,
      GROUP_CONCAT(year ORDER BY rate DESC) grouped_year
    FROM
      yourtable
    GROUP BY id) group_max
  ON yourtable.id = group_max.id
     AND FIND_IN_SET(year, grouped_year) BETWEEN 1 AND 5
ORDER BY
  yourtable.id, yourtable.year DESC;

请看小提琴 here .

请注意,如果有多行可以具有相同的费率,则应考虑在“费率”列而不是“年份”列上使用“组一致(按费率的不同费率顺序)”。

group_concat返回的字符串的最大长度是有限的,因此如果需要为每个组选择几条记录,则此操作很有效。

^{这个 original query 使用的用户变量和 ORDER BY 在派生表上;不能保证这两个怪癖的行为。修改后的答案如下。}

在mysql 5.x中,可以使用poor man的rank over partition来获得所需的结果。只需将表与自身进行外部连接,对于每一行,计算行数 较小的 比它。在上述情况下,较小的行是具有较高速率的行:

SELECT t.id, t.rate, t.year, COUNT(l.rate) AS rank
FROM t
LEFT JOIN t AS l ON t.id = l.id AND t.rate < l.rate
GROUP BY t.id, t.rate, t.year
HAVING COUNT(l.rate) < 5
ORDER BY t.id, t.rate DESC, t.year

Demo and Result :

| id  | rate | year | rank |
|-----|------|------|------|
| p01 |  8.0 | 2006 | 0    |
| p01 |  7.4 | 2003 | 1    |
| p01 |  6.8 | 2008 | 2    |
| p01 |  5.9 | 2001 | 3    |
| p01 |  5.3 | 2007 | 4    |
| p02 | 12.5 | 2001 | 0    |
| p02 | 12.4 | 2004 | 1    |
| p02 | 12.2 | 2002 | 2    |
| p02 | 10.3 | 2003 | 3    |
| p02 |  8.7 | 2000 | 4    |

请注意,如果费率有关联,例如:

100, 90, 90, 80, 80, 80, 70, 60, 50, 40, ...

上面的查询将返回6行:

100, 90, 90, 80, 80, 80

更改为 HAVING COUNT(DISTINCT l.rate) < 5 要获得8行:

100, 90, 90, 80, 80, 80, 70, 60

或改为 ON t.id = l.id AND (t.rate < l.rate OR (t.rate = l.rate AND t.pri_key > l.pri_key)) 要获得5行:

 100, 90, 90, 80, 80

在mysql 8或更高版本中,只需使用 RANK , DENSE_RANK or ROW_NUMBER 功能:

SELECT *
FROM (
    SELECT *, RANK() OVER (PARTITION BY id ORDER BY rate DESC) AS rnk
    FROM t
) AS x
WHERE rnk <= 5

对我来说

SUBSTRING_INDEX(group_concat(col_name order by desired_col_order_name), ',', N) 

工作得很好。没有复杂的问题。

例如:每组获得前1名

SELECT 
    *
FROM
    yourtable
WHERE
    id IN (SELECT 
            SUBSTRING_INDEX(GROUP_CONCAT(id
                            ORDER BY rate DESC),
                        ',',
                        1) id
        FROM
            yourtable
        GROUP BY year)
ORDER BY rate DESC;

不,不能任意限制子查询(在较新的mysqls中可以在有限的范围内这样做,但不能针对每个组5个结果)。

这是一个groupwise最大类型查询,这在sql中是很重要的。有 various ways 在某些情况下更有效地解决这个问题,但是对于top-n,您通常会想看看 Bill's answer 去问一个类似的问题。

与此问题的大多数解决方案一样,如果有多个行具有相同的 rate 值,因此您可能仍然需要大量的后处理来检查该值。

这需要一系列子查询来对值进行排序、限制它们,然后在分组时执行求和

@Rnk:=0;
@N:=2;
select
  c.id,
  sum(c.val)
from (
select
  b.id,
  b.bal
from (
select   
  if(@last_id=id,@Rnk+1,1) as Rnk,
  a.id,
  a.val,
  @last_id=id,
from (   
select 
  id,
  val 
from list
order by id,val desc) as a) as b
where b.rnk < @N) as c
group by c.id;

试试这个:

SELECT h.year, h.id, h.rate 
FROM (SELECT h.year, h.id, h.rate, IF(@lastid = (@lastid:=h.id), @index:=@index+1, @index:=0) indx 
      FROM (SELECT h.year, h.id, h.rate 
            FROM h
            WHERE h.year BETWEEN 2000 AND 2009 AND id IN (SELECT rid FROM table2)
            GROUP BY id, h.year
            ORDER BY id, rate DESC
            ) h, (SELECT @lastid:='', @index:=0) AS a
    ) h 
WHERE h.indx <= 5;

在oracle中构建虚拟列rowid

表:

`
CREATE TABLE `stack` 
(`year` int(11) DEFAULT NULL,
`id` varchar(10) DEFAULT NULL,
`rate` float DEFAULT NULL) 
ENGINE=InnoDB DEFAULT CHARSET=utf8mb4
`

数据:

insert into stack values(2006,'p01',8);
insert into stack values(2001,'p01',5.9);
insert into stack values(2007,'p01',5.3);
insert into stack values(2009,'p01',4.4);
insert into stack values(2001,'p02',12.5);
insert into stack values(2004,'p02',12.4);
insert into stack values(2005,'p01',2.1);
insert into stack values(2000,'p01',0.8);
insert into stack values(2002,'p02',12.2);
insert into stack values(2002,'p01',3.9);
insert into stack values(2004,'p01',3.5);
insert into stack values(2003,'p02',10.3);
insert into stack values(2000,'p02',8.7);
insert into stack values(2006,'p02',4.6);
insert into stack values(2007,'p02',3.3);
insert into stack values(2003,'p01',7.4);
insert into stack values(2008,'p01',6.8);

像这样的SQL:

select t3.year,t3.id,t3.rate 
from (select t1.*, (select count(*) from stack t2 where t1.rate<=t2.rate and t1.id=t2.id) as rownum from stack t1) t3 
where rownum <=3 order by id,rate DESC;

如果删除t3中的where子句,则显示如下:

获取“前n个记录”->在where子句(t3的where子句)中添加“rownum<=3”;

选择“年份”->在where子句(t3的where子句)中添加“2000到2009之间”;

做了一些工作,但是我认为我的解决方案是值得分享的,因为它看起来既优雅又快速。

SELECT h.year, h.id, h.rate 
  FROM (
    SELECT id, 
      SUBSTRING_INDEX(GROUP_CONCAT(CONCAT(id, '-', year) ORDER BY rate DESC), ',' , 5) AS l
      FROM h
      WHERE year BETWEEN 2000 AND 2009
      GROUP BY id
      ORDER BY id
  ) AS h_temp
    LEFT JOIN h ON h.id = h_temp.id 
      AND SUBSTRING_INDEX(h_temp.l, CONCAT(h.id, '-', h.year), 1) != h_temp.l

请注意,此示例是为问题的目的而指定的,并且可以很容易地为其他类似目的进行修改。

以下职位: sql: selcting top N record per group 描述在不使用子查询的情况下实现此目标的复杂方法。

它改进了这里提供的其他解决方案:

• 在单个查询中执行所有操作
• 能够正确利用索引
• 避免子查询,众所周知在mysql中会产生错误的执行计划

但它并不漂亮。如果在mysql中启用了窗口函数(也称为分析函数),一个很好的解决方案是可以实现的——但事实并非如此。 这篇文章中使用的技巧是使用group concat,它有时被描述为“mysql的穷人窗口函数”。

SELECT year, id, rate
FROM (SELECT
  year, id, rate, row_number() over (partition by id order by rate DESC)
  FROM h
  WHERE year BETWEEN 2000 AND 2009
  AND id IN (SELECT rid FROM table2)
  GROUP BY id, year
  ORDER BY id, rate DESC) as subquery
WHERE row_number <= 5

子查询几乎与您的查询相同。唯一的变化是添加

row_number() over (partition by id order by rate DESC)

对于像我这样有疑问的人。我做了以下的限制和其他任何由一个特定的小组。

DELIMITER $$
CREATE PROCEDURE count_limit200()
BEGIN
    DECLARE a INT Default 0;
    DECLARE stop_loop INT Default 0;
    DECLARE domain_val VARCHAR(250);
    DECLARE domain_list CURSOR FOR SELECT DISTINCT domain FROM db.one;

    OPEN domain_list;

    SELECT COUNT(DISTINCT(domain)) INTO stop_loop 
    FROM db.one;
    -- BEGIN LOOP
    loop_thru_domains: LOOP
        FETCH domain_list INTO domain_val;
        SET a=a+1;

        INSERT INTO db.two(book,artist,title,title_count,last_updated) 
        SELECT * FROM 
        (
            SELECT book,artist,title,COUNT(ObjectKey) AS titleCount, NOW() 
            FROM db.one 
            WHERE book = domain_val
            GROUP BY artist,title
            ORDER BY book,titleCount DESC
            LIMIT 200
        ) a ON DUPLICATE KEY UPDATE title_count = titleCount, last_updated = NOW();

        IF a = stop_loop THEN
            LEAVE loop_thru_domain;
        END IF;
    END LOOP loop_thru_domain;
END $$

它循环遍历一个域列表,然后每个域只插入200个限制

试试这个:

SET @num := 0, @type := '';
SELECT `year`, `id`, `rate`,
    @num := if(@type = `id`, @num + 1, 1) AS `row_number`,
    @type := `id` AS `dummy`
FROM (
    SELECT *
    FROM `h`
    WHERE (
        `year` BETWEEN '2000' AND '2009'
        AND `id` IN (SELECT `rid` FROM `table2`) AS `temp_rid`
    )
    ORDER BY `id`
) AS `temph`
GROUP BY `year`, `id`, `rate`
HAVING `row_number`<='5'
ORDER BY `id`, `rate DESC;

请尝试下面的存储过程。我已经核实过了。我得到了正确的结果,但没有使用 groupby .

CREATE DEFINER=`ks_root`@`%` PROCEDURE `first_five_record_per_id`()
BEGIN
DECLARE query_string text;
DECLARE datasource1 varchar(24);
DECLARE done INT DEFAULT 0;
DECLARE tenants varchar(50);
DECLARE cur1 CURSOR FOR SELECT rid FROM demo1;
DECLARE CONTINUE HANDLER FOR NOT FOUND SET done = 1;

    SET @query_string='';

      OPEN cur1;
      read_loop: LOOP

      FETCH cur1 INTO tenants ;

      IF done THEN
        LEAVE read_loop;
      END IF;

      SET @datasource1 = tenants;
      SET @query_string = concat(@query_string,'(select * from demo  where `id` = ''',@datasource1,''' order by rate desc LIMIT 5) UNION ALL ');

       END LOOP; 
      close cur1;

    SET @query_string  = TRIM(TRAILING 'UNION ALL' FROM TRIM(@query_string));  
  select @query_string;
PREPARE stmt FROM @query_string;
EXECUTE stmt;
DEALLOCATE PREPARE stmt;

END