How do I query the number of data that corresponds to a foreign key from a table based on the primary table ID?

For example, from the table of the Reid to the Main Table ID field how to query the ID of the main table corresponding to the data from the table foreign key number of bars? For example, Reid is 1 points to the main Table ID 1 row Then if only ID can query based on ID how many data?

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For example, from the table of the Reid to the Main Table ID field how to query the ID of the main table corresponding to the data from the table foreign key number of bars? For example, Reid is 1 points to the main Table ID 1 row Then if only ID can query based on ID how many data?

You need [JOIN]

For example, the main table is a, from the table is B, then you can probably write:

SELECT a.id,COUNT(b.reid) AS count_id FROM a INNER JOIN b ON a.id = b.reid GROUP BY a.id ORDER BY a.id, count_id;

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