mysql - 为 MySQL 重写 MS SQL 查询

Question

前一段时间，一位用户发布了一个有趣的查询，该查询是为 MS SQL 编写的，它依赖于公用表表达式 (CTE)。任何人都可以提供有关此查询对于 MySQL 的外观的任何方向吗？

我包括了整个示例，它还创建了一个包含一些示例数据的临时表。我只对 MySQL 的约会查询感兴趣。在查询下方，我发布了预期的输出。

原帖链接如下: HALF-an-hour and One-hour time slot booking based on selection- c# and sql

-- Sample data from the question.
declare @Appointment table
(
    [ID] bigint not null identity(1, 1), -- Primary key.
    [BookedDate] date not null,          -- The date of the appointment.
    [Time] time(0) not null,             -- The start time of the appointment.
    [Duration] int not null              -- The length of the appointment in minutes.
);
insert @Appointment
    ([BookedDate], [Time], [Duration])
values
    ('2014-04-15', '09:00', 60),
    ('2014-04-15', '10:00', 30),
    ('2014-04-15', '17:00', 60),
    ('2014-04-15', '18:30', 30);

-- @StartTime is the time the office opens on the desired date.
-- @EndTime is the time the office closes on the desired date.
-- @Interval is the number of minutes that separate potential appointment times.
-- @DesiredDate is the date on which an appointment is requested.
-- @DesiredLength is the length of the requested appointment in minutes.
declare @StartTime time(0) = '09:00';
declare @EndTime time(0) = '21:00';
declare @Interval int = 30;
declare @DesiredDate date = '2014-04-15';
declare @DesiredLength int = 30;

-- This CTE enumerates all potential timeslots on the @DesiredDate given the above data.
with [TimeSlotCTE] as
(
    -- Base case: the first appointment slot of the day.
    select 
        [From] = @StartTime, 
        [To] = dateadd(minute, @DesiredLength, @StartTime)

    union all

    -- Recursive case: create a subsequent appointment slot as long as doing so won't
    -- take us past the office's closing time.
    select
        dateadd(minute, @Interval, [From]),
        dateadd(minute, @Interval, [To])
    from
        [TimeSlotCTE]
    where
        dateadd(minute, @Interval, [To]) <= @EndTime
)

-- Finally, we simply select every time slot defined above for which there does not
-- yet exist an overlapping appointment on the requested date.
select
    [T].[From],
    [T].[To],
    [Available] = 
        case when exists 
        (
            select 1 from @Appointment [A]
            where
                -- Forgot this line the first time around!
                [A].[BookedDate] = @DesiredDate and
                [A].[Time] < [T].[To] and
                dateadd(minute, [A].[Duration], [A].[Time]) > [T].[From]
        )
        then 'No' else 'Yes' end
from
    [TimeSlotCTE] [T];

输出

From        To          Available
09:00:00    09:30:00    No
09:30:00    10:00:00    No
10:00:00    10:30:00    No
10:30:00    11:00:00    Yes
11:00:00    11:30:00    Yes
11:30:00    12:00:00    Yes
12:00:00    12:30:00    Yes
12:30:00    13:00:00    Yes
13:00:00    13:30:00    Yes
13:30:00    14:00:00    Yes
14:00:00    14:30:00    Yes
14:30:00    15:00:00    Yes
15:00:00    15:30:00    Yes
15:30:00    16:00:00    Yes
16:00:00    16:30:00    Yes
16:30:00    17:00:00    Yes
17:00:00    17:30:00    No
17:30:00    18:00:00    No
18:00:00    18:30:00    Yes
18:30:00    19:00:00    No
19:00:00    19:30:00    Yes
19:30:00    20:00:00    Yes
20:00:00    20:30:00    Yes
20:30:00    21:00:00    Yes

谢谢!

Answer 1

评论太长了。

您可以移至 MySQL 8+ 进行直接转换。 MySQL 现在支持公用表表达式 (CTE) 和递归 CTE。当然，代码会根据 MySQL 约定进行更改，但总体上是一样的。

另一种方法是在两个数据库中使用numbers 表来构造约会开始。从性能的角度来看，这可能是个好主意。