如何通过在mysql中使用join来获取数据

Question

我有一张桌子：

和这张表：

我想创建像这样的报告

我试过这个SQL：

select
    master_problem.problem,
    master_problem.sop_reference,
    master_problem.adidas_spec,
    count(log_roving_qc.id_problem) as jumlahfrom
master_problem
inner join log_roving_qc
    on master_problem.id_problem = log_roving_qc.id_problem
group by master_problem.id_problem

但空数据未显示。我想显示描述为0

的空白数据

Answer 1

将master_problem表左连接到执行计数聚合的子查询：

SELECT
    mp.problem,
    mp.sop_reference,
    mp.adidas_spec,
    COALESCE(t.cnt, 0) AS jumlahfrom
FROM master_problem mp
LEFT JOIN
(
    SELECT id_problem, COUNT(*) as cnt
    FROM log_roving_qc
    GROUP BY id_problem
) t
    ON mp.id_problem = t.id_problem;