HOUR_FLOOR

Description

The hour_floor function rounds down the input datetime value to the nearest moment of the specified hour period. For example, if the period is 5 hours, the function adjusts the input time to the starting hour mark within that period.

Date calculation formula:

$$\begin{aligned} &\text{hour\_floor}(\langle\text{date\_or\_time\_expr}\rangle, \langle\text{period}\rangle, \langle\text{origin}\rangle) = \\ &\max\{\langle\text{origin}\rangle + k \times \langle\text{period}\rangle \times \text{hour} \mid \\ &k \in \mathbb{Z} \land \langle\text{origin}\rangle + k \times \langle\text{period}\rangle \times \text{hour} \leq \langle\text{date\_or\_time\_expr}\rangle\} \end{aligned}$$

$k$ represents the number of periods from the baseline time to the target time.

Syntax

HOUR_FLOOR(`<date_or_time_expr>`)
HOUR_FLOOR(`<date_or_time_expr>`, `<origin>`)
HOUR_FLOOR(`<date_or_time_expr>`, `<period>`)
HOUR_FLOOR(`<date_or_time_expr>`, `<period>`, `<origin>`)

Parameters

Parameter	Description
<date_or_time_expr>	A valid date expression that supports datetime/date types. Date type will be converted to the start time 00:00:00 of the corresponding date. For specific datetime/date formats, please refer to datetime conversion and date conversion
<period>	Optional parameter that specifies the period length (unit: hours), must be a positive integer (such as 2, 6, 12). Default value is 1, representing one period every 1 hour
<origin>	The starting time origin, supports datetime/date types. If not provided, the default is 0001-01-01T00:00:00

Return Value

Returns a DATETIME type value representing the nearest period moment after rounding down.

• If the input period is a non-positive integer, returns error.
• If any parameter is NULL, the result returns NULL.
• If origin or datetime has scale, the returned result has scale.
• If the <origin> date and time is after the <period>, it will still be calculated according to the above formula, but the period k will be negative.

Examples

-- Round down by 5-hour period, default origin is 0001-01-01 00:00:00
mysql> select hour_floor("2023-07-13 22:28:18", 5);
+--------------------------------------+
| hour_floor("2023-07-13 22:28:18", 5) |
+--------------------------------------+
| 2023-07-13 18:00:00                  |
+--------------------------------------+

-- Using 2023-07-13 08:00 as origin, divide by 4-hour periods
mysql> select hour_floor('2023-07-13 19:30:00', 4, '2023-07-13 08:00:00') as custom_origin;
+---------------------+
| custom_origin       |
+---------------------+
| 2023-07-13 16:00:00 |
+---------------------+

-- Input datetime exactly at period edge, return input datetime value
select hour_floor("2023-07-13 18:00:00", 5);
+--------------------------------------+
| hour_floor("2023-07-13 18:00:00", 5) |
+--------------------------------------+
| 2023-07-13 18:00:00                  |
+--------------------------------------+

-- Input date type will be converted to start time 2023-07-13 00:00:00 of the day
mysql> select hour_floor('2023-07-13 20:30:00', 4, '2023-07-13');
+----------------------------------------------------+
| hour_floor('2023-07-13 20:30:00', 4, '2023-07-13') |
+----------------------------------------------------+
| 2023-07-13 20:00:00                                |
+----------------------------------------------------+

-- If origin or datetime has scale, the returned result has scale
mysql> select hour_floor('2023-07-13 19:30:00.123', 4, '2023-07-03 08:00:00') as custom_origin;
+-------------------------+
| custom_origin           |
+-------------------------+
| 2023-07-13 16:00:00.000 |
+-------------------------+

mysql> select hour_floor('2023-07-13 19:30:00', 4, '2023-07-03 08:00:00.123') as custom_origin;
+-------------------------+
| custom_origin           |
+-------------------------+
| 2023-07-13 16:00:00.123 |
+-------------------------+

--- If the <origin> date and time is after the <period>, it will still be calculated according to the above formula, but the period k will be negative.
select hour_floor('2023-07-13 19:30:00.123', 4, '2028-07-14 08:00:00') ;
+-----------------------------------------------------------------+
| hour_floor('2023-07-13 19:30:00.123', 4, '2028-07-14 08:00:00') |
+-----------------------------------------------------------------+
| 2023-07-13 16:00:00.000                                         |
+-----------------------------------------------------------------+

-- Input any parameter as NULL (returns NULL)
mysql> select hour_floor(null, 6) as null_input;
+------------+
| null_input |
+------------+
| NULL       |
+------------+

-- Period is negative, returns erro
mysql> select hour_floor('2023-12-31 23:59:59', -3);
ERROR 1105 (HY000): errCode = 2, detailMessage = (10.16.10.3)[E-218]Operation hour_floor of 2023-12-31 23:59:59, -3 out of range