--示例1：將字符串轉(zhuǎn)換為日期類型
SELECT TO_DATE('1994-07-01', 'YYYY-MM-DD') FROM DUAL;
--示例2：獲取系統(tǒng)當(dāng)前時(shí)間
SELECT SYSDATE FROM DUAL;
--示例3：計(jì)算兩個(gè)日期之間的差值
SELECT MONTHS_BETWEEN(TO_DATE('2022-07-01', 'YYYY-MM-DD'), TO_DATE('1980-05-20', 'YYYY-MM-DD')) FROM DUAL;
--示例4：將日期截取為年份
SELECT TRUNC(MONTHS_BETWEEN(SYSDATE, TO_DATE('1994-07-01', 'YYYY-MM-DD')) / 12) FROM DUAL;

--示例1：計(jì)算當(dāng)前年齡
SELECT TRUNC(MONTHS_BETWEEN(SYSDATE, TO_DATE('1980-05-20', 'YYYY-MM-DD')) / 12) AS AGE FROM DUAL;

--示例1：統(tǒng)計(jì)各年齡段人數(shù)
SELECT CASE
         WHEN age BETWEEN 18 AND 24 THEN '18-24歲'
         WHEN age BETWEEN 25 AND 30 THEN '25-30歲'
         WHEN age BETWEEN 31 AND 35 THEN '31-35歲'
         ELSE '其他年齡段'
       END AS age_group,
       COUNT(*) AS total
FROM (
       SELECT TRUNC(MONTHS_BETWEEN(SYSDATE, TO_DATE('1990-05-20', 'YYYY-MM-DD')) / 12) AS age
       FROM dual
       UNION ALL
       SELECT TRUNC(MONTHS_BETWEEN(SYSDATE, TO_DATE('1985-05-20', 'YYYY-MM-DD')) / 12) AS age
       FROM dual
       UNION ALL
       SELECT TRUNC(MONTHS_BETWEEN(SYSDATE, TO_DATE('1980-05-20', 'YYYY-MM-DD')) / 12) AS age
       FROM dual
       UNION ALL
       SELECT TRUNC(MONTHS_BETWEEN(SYSDATE, TO_DATE('1975-05-20', 'YYYY-MM-DD')) / 12) AS age
       FROM dual
       UNION ALL
       SELECT TRUNC(MONTHS_BETWEEN(SYSDATE, TO_DATE('1950-05-20', 'YYYY-MM-DD')) / 12) AS age
       FROM dual
)
GROUP BY CASE
           WHEN age BETWEEN 18 AND 24 THEN '18-24歲'
           WHEN age BETWEEN 25 AND 30 THEN '25-30歲'
           WHEN age BETWEEN 31 AND 35 THEN '31-35歲'
           ELSE '其他年齡段'
         END;

SELECT
  FLOOR(MONTHS_BETWEEN(sysdate, date_of_birth) / 12) AS age
FROM
  persons
WHERE
  date_of_birth = 'YYYY-MM-DD';

SELECT
  TRUNC(sysdate - date_of_birth) AS age_in_days
FROM
  persons
WHERE
  date_of_birth = 'YYYY-MM-DD';