SQL -- Update between two tables: update the fields of the other table with the fields of one table

-- 1. This statement is equivalent to a Left join statement. The where clause is the number of updates.

-- Note! If the number of rows in the table (obtained after where) is smaller than that in the outer table (obtained after where), a record that does not meet the = condition will be assigned a null value.

-- If NULL values are not incorrectly assigned, AN in (select...) must be added to the External table to force the records of the internal and external tables to be consistent.

1. UPDATEPatient
2. SETForeignName = (
3. SELECTForeignName_New
4. FROMPatient_YNG
5. WHEREPatient. PatientID = patient_yng.PatientID
6. )
7. WHEREPatient. ClinicID = 1483
8. ANDPatient. PatientIDIN(SELECTPatientid
9. FROMPatient_YNG)

-- 2. This method is easy and error-prone.

1. UPDATEPatient
2. SETForeignName = ForeignName_New
3. FROMPatient_YNG
4. WHEREPatient. PatientID = patient_yng.PatientID
5. ANDPatient. ClinicID = 1483