oracle数据库实现获取时间戳的无参函数

CREATE OR REPLACE FUNCTION GETMSTIMESTAMP
 RETURN NUMBER
 AS
 MSTIMESTAMP NUMBER;
 BEGIN
 SELECT (SYSDATE-TO_DATE('1970-1-18', 'YYYY-MM-DD HH24'))  86400000 + TO_NUMBER(TO_CHAR(SYSTIMESTAMP(3), 'FF')) INTO MSTIMESTAMP FROM DUAL;
 RETURN MSTIMESTAMP;
 END;

SELECT (SYSDATE - TO_DATE('1970-1-1 8', 'YYYY-MM-DD HH24'))  86400 FROM DUAL;
(SYSDATE-TO_DATE('1970-1-1 8','YYYY-MM-DDHH24'))86400
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1167040878

SELECT (SYSDATE - TO_DATE('1970-1-1 8', 'YYYY-MM-DD HH24'))  86400000 + TO_NUMBER(TO_CHAR(SYSTIMESTAMP(3), 'FF')) AS MILLIONS FROM DUAL;