In MySQL Query, how does one query a specified condition and query several additional data records?

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SELECT * FROM 'subobject' WHERE Subject_id IN (1602509) OR 1 = 1 LIMIT 5. for example, if the database contains a record Subject_id = 1602509, I want to query five records IN the result set, what should I do if it contains the record Subject_id = 1602509 ?? If there is no Subject_id = 1602509 record, use other data to complete 5 records.

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SELECT * FROM 'subobject' WHERE Subject_id IN (1602509) OR 1 = 1 LIMIT 5. for example, if the database contains a record Subject_id = 1602509, I want to query five records IN the result set, what should I do if it contains the record Subject_id = 1602509 ?? If there is no Subject_id = 1602509 record, use other data to complete 5 records.

SELECT * FROM 'subobject' WHERE Subject_id IN (1602509) union select * FROM 'subobject' WHERE Subject_id not in (1602509) LIMIT 5

In fact, this works.

Preferably at the business layer