# Task: 015

**Database:** retails  

## Question
For each industry, show the number of customers that bought part 309 from China.


## Gold Query

```sql
WITH industries AS (
SELECT DISTINCT c.c_mktsegment AS industry FROM customer c
),
china_customers AS (
SELECT
c.c_mktsegment AS industry,
COUNT(DISTINCT c.c_custkey) AS customer_count
FROM customer c
JOIN orders o ON c.c_custkey = o.o_custkey
JOIN lineitem l ON o.o_orderkey = l.l_orderkey
JOIN partsupp ps ON l.l_partkey = ps.ps_partkey AND l.l_suppkey = ps.ps_suppkey
JOIN supplier s ON ps.ps_suppkey = s.s_suppkey
JOIN nation n ON s.s_nationkey = n.n_nationkey
WHERE l.l_partkey = 309
AND n.n_name = 'CHINA'
GROUP BY c.c_mktsegment
ORDER BY c.c_mktsegment
)
SELECT
i.industry,
COALESCE(cc.customer_count, 0) AS customer_count
FROM industries i
LEFT JOIN china_customers cc ON i.industry = cc.industry
ORDER BY i.industry;
```

**Execution Result:**

| industry   |   customer_count |
|------------|------------------|
| AUTOMOBILE |                0 |
| BUILDING   |                0 |
| FURNITURE  |                0 |
| HOUSEHOLD  |                0 |
| MACHINERY  |                0 |

*5 rows*