How does one query the number of data entries corresponding to the foreign key of the table based on the primary table ID?

For example, how can I query the number of data entries corresponding to the foreign key of a table based on the id of the primary table from the table's reid to the id field of the primary table? For example, if reid is 1 and all point to the row with the primary table id 1, how many data entries can be queried by id?

For example, how can I query the number of data entries corresponding to the foreign key of a table based on the id of the primary table from the table's reid to the id field of the primary table? For example, if reid is 1 and all point to the row with the primary table id 1, how many data entries can be queried by id?

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For example, how can I query the number of data entries corresponding to the foreign key of a table based on the id of the primary table from the table's reid to the id field of the primary table? For example, if reid is 1 and all point to the row with the primary table id 1, how many data entries can be queried by id?

You need [JOIN]

For example, if the master table is a and the slave table is B, you can write it like this:

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;