SQL

Question

我需要获取 4 个表中每个 id_prevadzka 的计数：

首先我尝试了：

SELECT
    p.id_prevadzka,
    COUNT(pv.id_prevadzka) AS `vytoce_pocet`,
    COUNT(pn.id_prevadzka) AS `navstevy_pocet`,
    COUNT(pa.id_prevadzka) AS `akcie_pocet`,
    COUNT(ps.id_prevadzka) AS `servis_pocet`
FROM shop_prevadzky p
LEFT JOIN shop_prevadzky_vytoce pv ON (pv.id_prevadzka = p.id_prevadzka)
LEFT JOIN shop_prevadzky_navstevy pn ON (pn.id_prevadzka = p.id_prevadzka)
LEFT JOIN shop_prevadzky_akcie pa ON (pa.id_prevadzka = p.id_prevadzka)
LEFT JOIN shop_prevadzky_servis ps ON (ps.id_prevadzka = p.id_prevadzka)
GROUP BY p.id_prevadzka

但是这个 return 为 vytoce_pocet、navstevy_pocet、akcie_pocet 和 servis_pocet 编辑了相同的数字 - 这是数字，是什么在 shop_prevadzky_vytoce.

中计数

然后我尝试了 (as is answered here):

SELECT
    p.*,
    SUM(CASE WHEN pv.id_prevadzka IS NOT NULL THEN 1 ELSE 0 END) AS `vytoce_pocet`,
    SUM(CASE WHEN pn.id_prevadzka IS NOT NULL THEN 1 ELSE 0 END) AS `navstevy_pocet`,
    SUM(CASE WHEN pa.id_prevadzka IS NOT NULL THEN 1 ELSE 0 END) AS `akcie_pocet`,
    SUM(CASE WHEN ps.id_prevadzka IS NOT NULL THEN 1 ELSE 0 END) AS `servis_pocet`
FROM shop_prevadzky p
LEFT JOIN shop_prevadzky_vytoce pv ON (pv.id_prevadzka = p.id_prevadzka)
LEFT JOIN shop_prevadzky_navstevy pn ON (pn.id_prevadzka = p.id_prevadzka)
LEFT JOIN shop_prevadzky_akcie pa ON (pa.id_prevadzka = p.id_prevadzka)
LEFT JOIN shop_prevadzky_servis ps ON (ps.id_prevadzka = p.id_prevadzka)
WHERE p.cis_status = 1
GROUP BY p.id_prevadzka
ORDER BY p.prevadzka_nazov

但它 return 的结果与第一个示例中的结果相同。

我的第二个查询有什么问题？谢谢。

编辑：

为了更好理解，这可能是我表中的测试数据：

shop_prevadzky:

id_prevadzka
1
2

shop_prevadzky_vytoce:

id | id_prevadzka
1  | 1
2  | 1
3  | 1
4  | 1
5  | 2

shop_prevadzky_navstevy:

id | id_prevadzka
1  | 1
2  | 1

shop_prevadzky_akcie:

id | id_prevadzka
1  | 2

shop_prevadzky_服务:

id | id_prevadzka

并且查询应该 return:

id_prevadzka | vytoce_pocet | navstevy_pocet | akcie_pocet | servis_pocet
1              4              2                0             0
2              1              0                1             0

Answer 1

那是因为您要连接所有表并创建笛卡尔积

shop_prevadzky x _vytoce x _navstevy x _akcie x _servis

你可能想要

SELECT
    p.*,
    (SELECT COUNT(id_prevadzka) FROM shop_prevadzky_vytoce s WHERE s.id_prevadzka = p.id_prevadzka) AS `vytoce_pocet`,
    (SELECT COUNT(id_prevadzka) FROM shop_prevadzky_navstevy s WHERE s.id_prevadzka = p.id_prevadzka) AS `navstevy_pocet`,
    (SELECT COUNT(id_prevadzka) FROM shop_prevadzky_akcie s WHERE s.id_prevadzka = p.id_prevadzka) AS `akcie_pocet`,
    (SELECT COUNT(id_prevadzka) FROM shop_prevadzky_servis s WHERE s.id_prevadzka = p.id_prevadzka) AS `servis_pocet`
FROM shop_prevadzky p

你也可以对子查询做同样的事情

SELECT
    p.*,
    COALESCE(vytoce_count, 0) as vytoce_count,
    COALESCE(navstevy_count, 0) as navstevy_count,
    COALESCE(akcie_count, 0) as akcie_count,
    COALESCE(servis_count, 0) as servis_count
FROM shop_prevadzky p
LEFT JOIN  (SELECT id_prevadzka, COUNT(id_prevadzka) vytoce_count
            FROM shop_prevadzky_vytoce s 
            WHERE s.id_prevadzka = p.id_prevadzka) AS vytoce
       ON p.id_prevadzka = vytoce.id_prevadzka

LEFT JOIN  (SELECT id_prevadzka, COUNT(id_prevadzka) navstevy_count
            FROM shop_prevadzky_navstevy s 
            WHERE s.id_prevadzka = p.id_prevadzka) AS navstevy
       ON p.id_prevadzka = navstevy.id_prevadzka

LEFT JOIN  (SELECT id_prevadzka, COUNT(id_prevadzka) akcie_count
            FROM shop_prevadzky_akcie s 
            WHERE s.id_prevadzka = p.id_prevadzka) AS akcie
       ON p.id_prevadzka = akcie.id_prevadzka

LEFT JOIN  (SELECT id_prevadzka, COUNT(id_prevadzka) servis_count
            FROM shop_prevadzky_servis s 
            WHERE s.id_prevadzka = p.id_prevadzka) AS servis
       ON p.id_prevadzka = servis.id_prevadzka

Answer 2

尝试不同的计数，如：

使用您的数据样本

SQL Fiddle Demo

SELECT
    p.id_prevadzka,
    COUNT(distinct pv.id) AS `vytoce_pocet`,
    COUNT(distinct pn.id) AS `navstevy_pocet`,
    COUNT(distinct pa.id) AS `akcie_pocet`,
    COUNT(distinct ps.id) AS `servis_pocet`
FROM shop_prevadzky p
LEFT JOIN shop_prevadzky_vytoce pv ON (pv.id_prevadzka = p.id_prevadzka)
LEFT JOIN shop_prevadzky_navstevy pn ON (pn.id_prevadzka = p.id_prevadzka)
LEFT JOIN shop_prevadzky_akcie pa ON (pa.id_prevadzka = p.id_prevadzka)
LEFT JOIN shop_prevadzky_servis ps ON (ps.id_prevadzka = p.id_prevadzka)
GROUP BY p.id_prevadzka

输出

| id_prevadzka | vytoce_pocet | navstevy_pocet | akcie_pocet | servis_pocet |
|--------------|--------------|----------------|-------------|--------------|
|            1 |            4 |              2 |           0 |            0 |
|            2 |            1 |              0 |           1 |            0 |

Answer 3

这样怎么样：

SELECT
p.id_prevadzka,
(Select COUNT(pv.id_prevadzka) from shop_prevadzky_vytoce pv where pv.id_prevadzka = p.id_prevadzka) AS `vytoce_pocet`,
(Select COUNT(pn.id_prevadzka) from shop_prevadzky_navstevy pn where pn.id_prevadzka = p.id_prevadzka) AS `navstevy_pocet`,
(Select COUNT(pa.id_prevadzka) from shop_prevadzky_akcie pa Where pa.id_prevadzka = p.id_prevadzka) AS `akcie_pocet`,
(Select COUNT(ps.id_prevadzka) from shop_prevadzky_servis ps Where ps.id_prevadzka = p.id_prevadzka) AS `servis_pocet`
FROM shop_prevadzky p
WHERE p.cis_status = 1

Answer 4

您真的需要将此作为单个查询执行吗？为什么不是这样的：

select count(*) from foo;
select count(*) from bar;

或

select 'FOO_COUNT' as table_name, count(*) as cnt from foo
union all 
select 'BAR_COUNT' as table_name, count(*) as cnt from bar
;

SQL - 如何在多个表上使用更多的 COUNT？

SQL - How to use more COUNT on many tables?

mysql

left-join