子查询查出来的结果是一样的, where条件没有生效
SELECT
a.Id,
a.PatientName,
(SELECT dic.DiagnosisCode FROM op_opdiagnoses dic WHERE dic.OpRegisterId = a.Id ORDER BY dic.CreationTime DESC LIMIT 1) DiagnosisCode,
(SELECT di.DiagnosisName FROM op_opdiagnoses di WHERE di.OpRegisterId = a.Id ORDER BY di.CreationTime DESC LIMIT 1) DiagnosisName
FROM
op_opregisters a
