[数据库基础]——快速浏览日期时间转换

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数据库日期和时间类型

相互转换

    time ⇌ date

    time ⇌ smalldatetime

    time ⇌ datetime

    time ⇌ datetime2

    time ⇌ datetimeoffset

    date ⇌ smalldatetime

    date ⇌ datetime

    date ⇌ datetime2

    date ⇌ datetimeoffset

    smalldatetime ⇌ datetime

    smalldatetime ⇌ datetime2

    smalldatetime ⇌ datetimeoffset

    datetime ⇌ datetime2

    datetime ⇌ datetimeoffset

    datetime2 ⇌ datetimeoffset

 

 

数据库日期和时间类型：

类型	格式	范围
time	hh:mm:ss[.nnnnnnn]	00:00:00.0000000 ~ 23:59:59.9999999
date	YYYY-MM-DD	0001-01-01 ~ 9999-12-31
smalldatetime	YYYY-MM-DD hh:mm:ss	1900-01-01 ~ 079-06-06
datetime	YYYY-MM-DD hh:mm:ss[.nnn]	1753-01-01 ~ 99-12-31
datetime2	YYYY-MM-DD hh:mm:ss[.nnnnnnn]	0001-01-01 00:00:00.0000000 ~ 99-12-31 23:59:59.9999999
datetimeoffset	YYYY-MM-DD hh:mm:ss[.nnnnnnn] [+|-]hh:mm	0001-01-01 00:00:00.0000000 ~9999-12-31 23:59:59.9999999 (in UTC)

 

相互转换（SET DATEFORMAT dmy;）

 

time ⇌ date

---

-- time -> date
DECLARE @time time(4) = '12:15:04.1234';
DECLARE @date date= @time;

SELECT @time AS '@time', @date AS '@date';

Result：

Operand type clash: time is incompatible with date

---

-- date -> time
DECLARE @date date= '12-10-25';
DECLARE @time time= @date;

SELECT @date AS '@date', @time AS '@time';

Result：

Operand type clash: time is incompatible with date

 

time ⇌ smalldatetime

---

-- time -> smalldatetime
DECLARE @time time(4) = '12:15:04.1234';
DECLARE @smalldatetime smalldatetime= @time;

SELECT @time AS '@time', @smalldatetime AS '@smalldatetime';

Result：

@time               @smalldatetime
12:15:04.1234    1900-01-01 12:15:00

---

-- samlldatetime –> time
DECLARE @smalldatetime smalldatetime = '13-12-1995 12:43:10';
DECLARE @time time(4) = @smalldatetime;

SELECT @smalldatetime AS '@smalldatetime', @time AS 'time';

Result：

@smalldatetime        @time
1995-12-13 12:43:00    12:43:00.0000

 

time ⇌ datetime

---

-- time -> datetime
DECLARE @time time(4) = '12:10:05.1234';
DECLARE @datetime datetime = @time;

SELECT @time AS '@datetime', @datetime AS '@time';

Result：

@time                      @datetime
12:10:05.1234            1900-01-01 12:10:05.123

---

-- datetime -> time
DECLARE @datetime datetime = '12-11-05 12:10:05.123';
DECLARE @time time(4) = @datetime;

SELECT @datetime AS '@datetime', @time AS '@time';

Result：

@datetime                       @time
2005-11-12 12:10:05.123    12:10:05.1230

 

time ⇌ datetime2

---

-- time -> datetime2
DECLARE @time time(4) = '12:15:04.1234';
DECLARE @datetime2 datetime2(3) = @time;

SELECT @datetime2 AS '@datetime2', @time AS '@time';

Result：

@time               @datetime2
12:15:04.1234    1900-01-01 12:15:04.123

---

-- datetime2 -> time
DECLARE @datetime2 datetime2(4) = '12-10-25 12:32:10.1234';
DECLARE @time time(3) = @datetime2;

SELECT @datetime2 AS '@datetime2', @time AS '@time(3)';

Result：

@datetime2                       @time(3)
2025-10-12 12:32:10.1234    12:32:10.123

 

time ⇌ datetimeoffset

---

-- time -> datetimeoffset
DECLARE @time time(4) = '12:15:04.1234';
DECLARE @datetimeoffset datetimeoffset(3) = @time;

SELECT @time AS '@time', @datetimeoffset AS '@datetimeoffset';

Result：

@time              @datetimeoffset
12:15:04.1234    1900-01-01 12:15:04.123 +00:00

---

-- datetimeoffset -> time
DECLARE @datetimeoffset datetimeoffset(4) = '12-10-25 12:32:10.1234 +01:0';
DECLARE @time time(3) = @datetimeoffset;

SELECT @datetimeoffset AS '@datetimeoffset ', @time AS '@time';

Result：

@datetimeoffset                           @time
2025-10-12 12:32:10.1234 +01:00    12:32:10.123

 

date ⇌ smalldatetime

---

-- date -> smalldatetime
DECLARE @date date= '1912-10-25';
DECLARE @smalldatetime smalldatetime = @date;

SELECT @date AS '@date', @smalldatetime AS '@smalldatetime';

Result：

@date          @smalldatetime
1912-10-25    1912-10-25 00:00:00

---

-- smalldatetime -> date
DECLARE @smalldatetime smalldatetime = '13-12-1955 12:43:10';
DECLARE @date date = @smalldatetime

SELECT @smalldatetime AS '@smalldatetime', @date AS '@date';

Result：

@smalldatetime        @date
1955-12-13 12:43:00    1955-12-13

 

date ⇌ datetime

---

-- date -> datetime
DECLARE @date date= '12-10-25';
DECLARE @datetime datetime= @date;

SELECT @date AS '@date', @datetime AS '@datetime';

Result：

@date           @datetime
2025-10-12    2025-10-12 00:00:00.000

---

-- datetime -> date
DECLARE @datetime datetime = '12-11-05 12:43:10';
DECLARE @date date = @datetime;

SELECT @datetime AS '@datetime', @date AS '@date';

Result：

@datetime                        @date
2005-11-12 12:43:10.000    2005-11-12

 

date ⇌ datetime2

---

-- date -> datetime2
DECLARE @date date = '25-10-2030'
DECLARE @datetime2 datetime2(3) = @date;

SELECT @date AS '@date', @datetime2 AS '@datetime2(3)';

Result：

@date           @datetime2(3)
2030-10-25    2030-10-25 00:00:00.000

---

-- datetime2 -> date
DECLARE @datetime2 datetime2(4) = '12-10-25 12:32:10.1234';
DECLARE @date date = @datetime2;

SELECT @datetime2 AS '@datetime2', @date AS '@date';

Result：

@datetime2                        @date
2025-10-12 12:32:10.1234    2025-10-12

 

date ⇌ datetimeoffset

---

-- date -> datetimeoffset
DECLARE @date date = '1912-10-25';
DECLARE @datetimeoffset datetimeoffset(3) = @date;

SELECT @date AS '@date', @datetimeoffset AS '@datetimeoffset';

Result：

@date           @datetimeoffset
1912-10-25    1912-10-25 00:00:00.000 +00:00

---

-- datetimeoffset -> date
DECLARE @datetimeoffset datetimeoffset(4) = '12-10-25 12:32:10 +01:0';
DECLARE @date date= @datetimeoffset;

SELECT @datetimeoffset AS '@datetimeoffset ', @date AS '@date';

Result：

@datetimeoffset                             @date
2025-10-12 12:32:10.0000 +01:00    2025-10-12

 

smalldatetime ⇌ datetime

 

-- smalldatetime -> datetime
DECLARE @smalldatetime smalldatetime = '12-10-2040 12:43:10';
DECLARE @datetime datetime = @smalldatetime;

SELECT @smalldatetime AS '@smalldatetime', @datetime AS '@datetime';

Result：

@smalldatetime          @datetime
2040-10-12 12:43:00    2040-10-12 12:43:00.000

---

-- datetime -> smalldatetime
DECLARE @datetime datetime = '12-11-05 12:43:10.123';
DECLARE @smalldatetime smalldatetime = @datetime;

SELECT @datetime AS 'datetime', @smalldatetime AS '@smalldatetime';

Result：

datetime                           @smalldatetime
2005-11-12 12:43:10.123    2005-11-12 12:43:00

 

smalldatetime ⇌ datetime2

---

-- smalldatetime -> datetime2
DECLARE @smalldatetime smalldatetime = '12-06-2011 12:43:10';
DECLARE @datetime2 datetime2(4) = @smalldatetime;

SELECT @smalldatetime AS '@smalldatetime', @datetime2 AS '@datetime2(4)';

Result：

@smalldatetime          @datetime2(4)
2011-06-12 12:43:00    2011-06-12 12:43:00.0000

---

-- datetime2 -> smalldatetime
DECLARE @datetime2 datetime2 = '12-10-25 12:32:10.1234567';
DECLARE @smalldatetime smalldatetime = @datetime2;

SELECT @datetime2 AS '@datetime2', @smalldatetime AS '@smalldatetime';

Result：

@datetime2                             @smalldatetime
2025-10-12 12:32:10.1234567    2025-10-12 12:32:00

 

smalldatetime ⇌ datetimeoffset

---

-- samlldatetime -> datetimeoffset
DECLARE @smalldatetime smalldatetime = '12-10-2013 12:43:10';
DECLARE @datetimeoffset datetimeoffset(4) = @smalldatetime;

SELECT @smalldatetime AS '@smalldatetime', @datetimeoffset AS '@datetimeoffset(4)';

Result：

@smalldatetime          @datetimeoffset(4)
2013-10-12 12:43:00    2013-10-12 12:43:00.0000 +00:00

---

-- datetimeoffset -> smalldatetime
DECLARE @datetimeoffset datetimeoffset(3) = '1912-10-25 12:24:32 +10:0';
DECLARE @smalldatetime smalldatetime = @datetimeoffset;

SELECT @datetimeoffset AS '@datetimeoffset', @smalldatetime AS '@smalldatetime';

Result：

@datetimeoffset                            @smalldatetime
1912-10-25 12:24:32.000 +10:00    1912-10-25 12:25:00

 

datetime ⇌ datetime2

---

-- datetimes -> datetime2
DECLARE @datetime datetime = '10-10-2014 12:45:37.123';
DECLARE @datetime2 datetime2(4) = @datetime;

SELECT @datetime AS '@datetime', @datetime2 AS '@datetime2';

Result：

@datetime                        @datetime2
2014-10-10 12:45:37.123    2014-10-10 12:45:37.1230

---

-- datetimes2 -> datetime
DECLARE @datetime2 datetime2(4) = '1968-10-23 12:45:37.1237';
DECLARE @datetime datetime = @datetime2;

SELECT @datetime2 AS '@datetime2', @datetime AS '@datetime';

Result：

@datetime2                        @datetime
1968-10-23 12:45:37.1237    1968-10-23 12:45:37.123

 

datetime ⇌ datetimeoffset

---

-- datetime -> datetimeoffset
DECLARE @datetime datetime = '12-10-25 12:32:10.123';
DECLARE @datetimeoffset datetimeoffset = @datetime;

SELECT @datetime AS '@datetime ', @datetimeoffset AS '@datetimeoffset';

Result：

@datetime                        @datetimeoffset
2025-10-12 12:32:10.123    2025-10-12 12:32:10.1230000 +00:00

---

-- datetimeoffset -> datetime
DECLARE @datetimeoffset datetimeoffset(4) = '12-10-25 12:32:10.1234 +01:0';
DECLARE @datetime datetime = @datetimeoffset;

SELECT @datetimeoffset AS '@datetimeoffset ', @datetime AS '@datetime';

Result：

@datetimeoffset                             @datetime
2025-10-12 12:32:10.1234 +01:00    2025-10-12 12:32:10.123

 

datetime2 ⇌ datetimeoffset

---

-- datetime2 -> datetimeoffset
DECLARE @datetime2 datetime2(3) = '12-10-25 12:32:10.1234567';
DECLARE @datetimeoffset datetimeoffset(2) = @datetime2;

SELECT @datetime2 AS '@datetime2', @datetimeoffset AS '@datetimeoffset(2)';

Result：

@datetime2                      @datetimeoffset(2)
2025-10-12 12:32:10.123    2025-10-12 12:32:10.12 +00:00

 

-- datetimeoffset -> datetime2
DECLARE @datetimeoffset datetimeoffset(4) = '1912-10-25 12:24:32.1234 +10:0';
DECLARE @datetime2 datetime2(3)= @datetimeoffset;

SELECT @datetimeoffset AS '@datetimeoffset', @datetime2 AS '@datetime2';

Result：

@datetimeoffset                             @datetime2
1912-10-25 12:24:32.1234 +10:00    1912-10-25 12:24:32.123