根据其他列 PSQL 的值在 SELECT 语句中添加附加列

Question

我有一张每人驾驶执照的表格，并且知道某人何时获得驾驶执照。驾照的有效期可以是您获得驾照之日起 X 天，也可以是特定日期。

 acquired        relative      specific_date      valid_type     expiration_date
----------------------------------------------------------------------------------
2015-02-05         500             null              days
2015-02-05         null         2016-03-05           date
2015-02-05         200             null              days
2015-02-05         null         2016-02-22           date

我现在的查询是：

SELECT acquired,
       relative_date,
       specific_date,
       valid_type
FROM person_drivers_license
WHERE (valid_type = 'days'
       AND (EXTRACT(epoch
                    FROM acquired) - EXTRACT(epoch
                                             FROM now()))/86400 + relative_date > 0)
  OR (valid_type = 'DATE'
      AND specific_date >= now()));

我正在尝试使用上面的 select 语句添加 expire_date 列。如果是特定日期，只需将日期放入 expire_date 中，如果是相对日期，则在获取日期的帮助下计算到期日期。这在 PSQL 中可行吗？

Answer 1

你不需要pl/sql

SELECT acquired,
       relative_date,
       specific_date,
       valid_type,
       CASE WHEN specific date = "date" -- starts here
       THEN specific date 
       ELSE acquired + cast('1 months' as interval)END 
       AS expiration_date -- end here
FROM person_drivers_license
WHERE (valid_type = 'days'
       AND (EXTRACT(epoch
                    FROM acquired) - EXTRACT(epoch
                                             FROM now()))/86400 + relative_date > 0)
  OR (valid_type = 'DATE'
      AND specific_date >= now()));

Answer 2

首先 - 在 postgres 中有一种更简单的日期数学运算方法。你可以使用类似的东西：

acquired + relative_date * interval '1 day' >= current_date

或

acquired + relative_date >= current_date 
-- any integer can be treated as interval in days for date mathematics is SQL

对于这个问题 - 试试这个：

CASE WHEN valid_type = 'days' 
     THEN acquired + relative_date * interval '1 day'
     WHEN valid_type = 'date'
     THEN specific_date
     --ELSE ??? you may specify something here
END

或

COALESCE(specific_date, acquired + relative_date * interval '1 day')

查询可能如下所示：

SELECT acquired,
       relative_date,
       specific_date,
       valid_type,
       COALESCE(specific_date, acquired + relative_date * interval '1 day') as valid_date
FROM person_drivers_license
WHERE COALESCE(specific_date, acquired + relative_date * interval '1 day') >= current_date

Answer 3

试试这个：

SELECT acquired,
       relative_date,
       specific_date,
       valid_type
       CASE valid_type
         WHEN 'days' THEN acquired + relative_date
         WHEN 'date' THEN specific_date
         ELSE NULL
       END AS expiration_date
FROM   person_drivers_license;