Oracle 从身份证计算年龄

CREATE OR REPLACE FUNCTION AGE_IN_IDCARD ( parameter VARCHAR2 ) 
RETURN NUMBER 
IS 
val DATE;
BEGIN
    IF parameter is NULL THEN
        RETURN -1;
    ELSE
        val := CASE WHEN LENGTH(parameter) <= 15 THEN 
                TO_DATE( '19'||NVL( SUBSTR( parameter, 7, 6 ), 'a' ), 'yyyy-MM-dd' )
            ELSE 
                TO_DATE( NVL( SUBSTR( parameter, 7, 8 ), 'a' ), 'yyyy-MM-dd' ) 
            END;
    END IF;
        
    RETURN TRUNC( ( TO_CHAR( SYSDATE, 'yyyyMMdd' ) - TO_CHAR( val, 'yyyyMMdd' ) ) / 10000 );
    EXCEPTION 
        WHEN OTHERS THEN
        RETURN - 1;
    
END;