如何计算 MySQL 中按行分组的多列？

Question

我有两个表，“关键字”和“统计数据”，想知道每个关键字每个商家有多少结果。 所以每个关键字一行。

期望的结果，例如：

KWD    | RESULTS Amazon | RESULTS eBay
test     3                5
second   6                2

表：

create table keywords
(
    ID           mediumint unsigned auto_increment
        primary key,
    KEYWORD      varchar(255)                                                     null
);

create table stats
(
    MERCHANT_ID tinyint unsigned                   not null,
    TYPE_ID     mediumint unsigned                 not null comment 'the ID of the coresponding type. E.g. kw_id from keywords',
    RESULTS     smallint unsigned                  null,
    DATE        date                               not null,
    primary key (DATE, MERCHANT_ID, TYPE_ID)
)
    comment 'How many results does each merchant have per search?';

样本数据：

-- keywords
insert into test.keywords (ID, KEYWORD) values (1, 'testing');
insert into test.keywords (ID, KEYWORD) values (2, 'blablub');

-- stats
insert into test.stats (MERCHANT_ID, TYPE_ID, RESULTS, DATE) values (1, 1, 33, '2021-07-06');
insert into test.stats (MERCHANT_ID, TYPE_ID, RESULTS, DATE) values (1, 2, 3, '2021-07-06');
insert into test.stats (MERCHANT_ID, TYPE_ID, RESULTS, DATE) values (2, 1, 22, '2021-07-06');
insert into test.stats (MERCHANT_ID, TYPE_ID, RESULTS, DATE) values (2, 2, 6, '2021-07-06');

查询：

select
       kwd.KEYWORD,
       mss.MERCHANT_ID,
       mss.RESULTS
from keywords kwd
LEFT JOIN stats mss ON mss.TYPE_ID = kwd.ID
where
    date = 20210705
group by kwd.ID

大约有10个商人。 是否可以为每个关键字获取一行并在单独的列中获得每个商家的结果数量？

Answer 1

尝试这样的事情：

select
  kwd.KEYWORD,
  SUM(IF(mss.MERCHANT_ID = 'amazon', mss.RESULTS, 0)) as `amazon_sum`,
  SUM(IF(mss.MERCHANT_ID = 'eBay', mss.RESULTS, 0)) as `eBay_sum`
    
from keywords kwd
    LEFT JOIN stats mss ON mss.TYPE_ID = kwd.ID
    where
        date = 20210705
    group by kwd.ID