从一个 table 中的多个日期时间列中查找最早的非 NULL 日期时间

Question

我的数据库 (SQL Server 2012) 中有一个 table，它包含多个日期时间字段。假设所有字段都可以为空。我试图找到每行存在的最早的非 NULL 日期。

我尝试的解决方案是使用可怕的 CASE 表达式：

--To return the earliest non-NULL time that exists from table tmp
--Datetime fields are dt_lab_instrument, dt_lab_scan, dt_arrived, dt_receipted

SELECT
    CASE
        WHEN tmp.dt_lab_instrument IS NOT NULL AND tmp.dt_lab_instrument <= tmp.dt_lab_scan AND tmp.dt_lab_instrument <= tmp.dt_arrived AND tmp.dt_lab_instrument <= tmp.dt_receipted THEN tmp.dt_lab_instrument
        WHEN tmp.dt_lab_scan IS NOT NULL AND tmp.dt_lab_scan <= tmp.dt_lab_instrument AND tmp.dt_lab_scan <= tmp.dt_arrived AND tmp.dt_lab_scan <= tmp.dt_receipted THEN tmp.dt_lab_scan
        WHEN tmp.dt_arrived IS NOT NULL AND tmp.dt_arrived <= tmp.dt_lab_instrument AND tmp.dt_arrived <= tmp.dt_lab_scan AND tmp.dt_arrived <= tmp.dt_receipted THEN tmp.dt_arrived
        WHEN tmp.dt_receipted IS NOT NULL AND tmp.dt_receipted <= tmp.dt_lab_instrument AND tmp.dt_receipted <= tmp.dt_lab_scan AND tmp.dt_receipted <= tmp.dt_arrived THEN tmp.dt_receipted
        ELSE '1990-01-01' --If all else fails return dummy date value
    END
from tmp

这很丑陋，效率低下，不处理空值，难以扩展（即尝试添加更多日期字段！）而且看起来是错误的。但我似乎对如何更好地解决这个问题有心理障碍。

我知道我可以通过使用 ISNULL 函数将任何 NULL 日期时间值替换为遥远未来的日期来处理空值，但这似乎只会让丑陋的代码变得更加丑陋。

有人可以帮我更好更有效地解决这个问题吗？非常感谢

Answer 1

如果我没猜错，你想获得这 4 个字段中最早的一个

dt_lab_instrument
dt_lab_scan
dt_arrived
dt_receipted

因此，您可以使用 MIN() 函数获取此字段中的 select 所有最小值，然后 select 来自此字段的最小值

SELECT MIN(C)
    FROM (VALUES 
    (SELECT MIN(dt_lab_instrument) from tmp where dt_lab_instrument is not null),
    (SELECT MIN(dt_lab_scan) from tmp where dt_lab_instrument is not null),
    (SELECT MIN(dt_arrived) from tmp where dt_lab_instrument is not null),
    (SELECT MIN(dt_receipted) from tmp where dt_lab_instrument is not null) 
    AS v (C)

Answer 2

使用 VALUES() 运算符将日期列反透视为行，并 MIN() 查找最早的

select *
from   tmp t
       cross apply
       (
           select min(dt) as min_dt
           from
           (
               values (dt_lab_instrument), (dt_lab_scan), (dt_arrived), (dt_receipted)
           ) m (dt)
       ) m

处理If all else fails return dummy date value，可以使用

ISNULL(min(dt), '1990-01-01')

或

COALESCE(min(dt), '1990-01-01')

从一个 table 中的多个日期时间列中查找最早的非 NULL 日期时间

Find earliest non-NULL datetime from several datetime columns in one table

sql

tsql

sql-server

sql-server-2012