Question

我有两张桌子。一个人的姓名（司机）和一个与他们的驾驶执照（许可证）细节和到期。我需要合并这两个表并列出驱动程序的名称，ID号以及许可证是否已过期。

我有以下内容返回所有带有许可证和到期日的驱动程序，但我想添加一个最终列，根据返回的到期日期（时间戳）声明（已过期/有效）。

SELECT d.name AS 'Driver Name', d.nric AS 'NRIC', l.expiry AS 'Expiry' FROM drivers d, licenses l WHERE d.driverID=licenses.driverID ORDER BY name ASC

我需要添加第四列，评估l.expiry今天是否“小于”，即过期。

输出应该是这样的：

Driver Name NRIC Expiry Validity
Joe Blooggs 1234 1/1/14 Valid
Joe Blooggy 1235 1/3/14 Invalid

有办法做到这一点吗？

Answer 1

SQL Fiddle

MySQL 5.5.32架构设置：

CREATE TABLE drivers
    (`driverID` int, `name` varchar(11), `nric` int)
;

INSERT INTO drivers
    (`driverID`, `name`, `nric`)
VALUES
    (1, 'Joe Blooggs', 1234),
    (2, 'Joe Blooggy', 1235)
;

CREATE TABLE licenses
    (`licenseID` int, `driverID` int, `expiry` int)
;

INSERT INTO licenses
    (`licenseID`,`driverID`, `expiry`)
VALUES
    (1,1, 1406217600),
    (2,1, 1409217600),
    (3,1, 1432656000),
    (4,2, 1406217600)
;

查询1 ：

SELECT d.name AS 'Driver Name', d.nric AS 'NRIC', l.expiry AS 'Expiry',
CASE
    WHEN l.expiry < UNIX_TIMESTAMP(NOW()) THEN "Invalid"
    ELSE "Valid"
END AS Validity
FROM drivers d 
INNER JOIN licenses l ON d.driverID=l.driverID and l.licenseID = 
                                       (select licenseID 
                                          from licenses l2 
                                          where l.driverID = l2.driverID 
                                          order by expiry desc limit 1)

<强> Results ：

| DRIVER NAME | NRIC |     EXPIRY | VALIDITY |
|-------------|------|------------|----------|
| Joe Blooggs | 1234 | 1432656000 |    Valid |
| Joe Blooggy | 1235 | 1406217600 |  Invalid |

Answer 2

其他答案建议不需要CASE：

SELECT d.name, l.expiry < NOW() AS expired
FROM drivers AS d

列expired将是布尔类型。

使用主机代码显示类似＆＃34;已过期的字符串＆＃34;并且＆＃34;没有过期＆＃34;基于类似（python）("expired", "active")[row.expired]的东西。这将节省db-server上有价值的cpu周期和网络带宽。

Answer 3

SELECT d.name AS 'Driver Name', d.nric AS 'NRIC', 
SELECT (sub_l.expiry as 'expiry' FROM licenses sub_l 
WHERE sub_l.driverID = d.driverID
AND sub_l.licenseID = l.licenseID),
CASE 
WHEN EXISTS(SELECT sub_l.expiry FROM licenses sub_l 
            WHERE sub_l.driverID = d.driverID
            AND sub_l.licenseID = l.licenseID
            AND sub_l.expiry > NOW()) 
     THEN 0
     ELSE 1
END AS is_expired
FROM drivers d JOIN licences l ON d.driverID = licenses.driverID
GROUP BY d.name, d.nric
ORDER BY d.name ASC

Answer 4

是的，请使用CASE表达式。

select
  d.name
  , d.nrci
  , l.expiry
  , case when l.expiry < current_date then 'Invalid' else 'Valid' end as Validity
  ...

MySQL - 如果日期过期（即小于今天的日期），如何向选择查询添加“标志”列？

4 个答案: