如何在 mysql 中使用单个查询从另一个 table（没有数据时为零）获取计数？

Question

我有两个 tables - 'Offered' 和 'joined'。我需要从加入的 table 中计数 'offered_id'，如果找不到则为零。我的 tables 和所需的输出如下。如何使用 mysql 中的单个查询实现此目的？

TABLE : OFFERED
===============
offered_id    data
-----------   ----
    1         aaaa
    2         bbbb
    3         cccc
    4         dddd
    5         eeee
    6         ffff

TABLE : JOINED
===============
joined_id      offered_id
-----------    ----------
    1               5
    2               2
    3               2
    4               1
    5               3
    6               2
    7               5

OUTPUT REQUIRED
===============
offered_id      data     count(offered_id) from joined table.(0 for no entry)
-----------    -----     ------------------------------------------------
    1           aaaa          1
    2           bbbb          3
    3           cccc          1
    4           dddd          0
    5           eeee          1
    6           ffff          0

Answer 1

使用子查询你可以实现...

SELECT OFFERED.offered_id, OFFERED.data, (SELECT COUNT(JOINED.joined_id) FROM JOINED WHERE JOINED.offered_id = OFFERED.offered_id) AS count_joined FROM OFFERED

Answer 2

使用count：

SELECT OFFERED.OFFERED_id,OFFERED.data,(select count(JOINED.joined_id) FROM JOINED INNER JOIN OFFERED
ON JOINED.offered_id = OFFERED.offered_id) as count_joined FROM OFFERED

Answer 3

试一试它可以帮助我为我的项目实现同样的目标，它一定会对你有所帮助。

SELECT offered_id FROM OFFERED WHERE offered_id IN (SELECT DISTINCT offered_id FROM JOINED)

如何在 mysql 中使用单个查询从另一个 table（没有数据时为零）获取计数？

How to get count from another table (zero when no data) using single query in mysql?

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