转载自：http://www.mysqltutorial.org/mysql-time/
Mastering MySQL TIME Data Type
Summary: in this tutorial, we will introduce you to the MySQL TIME data type and show you useful temporal functions to manipulate time data effectively.
Introduction to MySQL TIME data type
MySQL uses the 'HH:MM:SS' format for querying and displaying a time value that represents a time of day, which is within 24 hours. To represent a time interval between two events, MySQL uses the 'HHH:MM:SS' format, which is larger than 24 hours.
To define a TIME column, you use the following syntax:
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column_name
TIME;
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For example, the following snippet defines a column named start_at with TIME data type.
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start_at
TIME;
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A TIME value ranges from -838:59:59 to 838:59:59. In addition, a TIME value can have fractional seconds part that is up to microseconds precision (6 digits). To define a column whose data type is TIMEwith a fractional second precision part, you use the following syntax:
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column_name
TIME(N);
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N is an integer that represents the fractional part, which is up to 6 digits.
The following snippet defines a column with TIME data type including 3 digits of fractional seconds.
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begin_at
TIME(3);
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A TIME value takes 3 bytes for storage. In case a TIME value includes fractional second precision, it will take additional bytes based on the number of digits of the fractional second precision. The following table illustrates the storage required for fractional second precision.
| Fractional Second Precision | Storage (BYTES) |
| 0 | 0 |
| 1, 2 | 1 |
| 3, 4 | 2 |
| 5, 6 | 3 |
For example, TIME and TIME(0) takes 3 bytes. TIME(1) and TIME(2) takes 4 bytes (3 + 1); TIME(3) and TIME(6) take 5 and 6 bytes.
MySQL TIME data type example
Let’s take a look at an example of using the TIME data type for columns in a table.
First, create a new table named tests that consists of four columns: id, name, start_at, and end_at. The data types of the start_at and end_at columns are TIME.
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CREATE TABLE tests (
id INT PRIMARY KEY AUTO_INCREMENT,
name VARCHAR(255) NOT NULL,
start_at TIME,
end_at TIME
);
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Second, insert a row into the tests table.
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INSERT INTO tests(name,start_at,end_at)
VALUES('Test 1', '08:00:00','10:00:00');
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Third, query data from the tests table.
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SELECT
name, start_at, end_at
FROM
tests;
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Notice that we use 'HH:MM:SS' as the literal time value in the INSERT statement. Let’s examine all the valid time literals that MySQL can recognize.
MySQL TIME literals
MySQL recognizes various time formats besides the 'HH:MM:SS' format that we mentioned earlier.
MySQL allows you to use the 'HHMMSS' format without delimiter ( : ) to represent time value. For example, '08:30:00' and '10:15:00' can be rewritten as '083000' and '101500'.
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INSERT INTO tests(name,start_at,end_at)
VALUES('Test 2','083000','101500');
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However, 108000 is not a valid time value because 80 does not represent the correct minute. In this case, MySQL will raise an error if you try to insert an invalid time value into a table.
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INSERT INTO tests(name,start_at,end_at)
VALUES('Test invalid','083000','108000');
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MySQL issued the following error message after executing the above statement.
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Error
Code: 1292. Incorrect time value: '108000' for column 'end_at' at row 1
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In addition to the string format, MySQL accepts the HHMMSS as a number that represents a time value. You can also use SS, MMSS. For example, instead of using '082000', you can use 082000 as follows:
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INSERT INTO tests(name,start_at,end_at)
VALUES('Test 3',082000,102000);
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For the time interval, you can use the 'D HH:MM:SS' format where D represents days with a range from 0 to 34. A more flexible syntax is 'HH:MM', 'D HH:MM', 'D HH', or 'SS'.
If you use the delimiter:, you can use 1 digit to represent hours, minutes, or seconds. For example, 9:5:0 can be used instead of '09:05:00'.
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INSERT INTO tests(name,start_at,end_at)
VALUES('Test 4','9:5:0',100500);
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Useful MySQL TIME functions
MySQL provides several useful temporal functions for manipulating TIME data.
Getting to know the current time
To get the current time of the database server, you use the CURRENT_TIME function. The CURRENT_TIMEfunction returns the current time value as a string ( 'HH:MM:SS') or a numeric value ( HHMMSS) depending on the context where the function is used.
The following statements illustrate the CURRENT_TIME function in both string and numeric contexts:
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SELECT
CURRENT_TIME() AS string_now,
CURRENT_TIME() + 0 AS numeric_now;
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Adding and Subtracting time from a TIME value
To add a TIME value to another TIME value, you use the ADDTIME function. To subtract a TIME value from another TIME value, you use the SUBTIME function.
The following statement adds and subtracts 2 hours 30 minutes to and from the current time.
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SELECT
CURRENT_TIME(),
ADDTIME(CURRENT_TIME(), 023000),
SUBTIME(CURRENT_TIME(), 023000);
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In addition, you can use the TIMEDIFF() function to get a difference between two TIME values.
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SELECT
TIMEDIFF(end_at, start_at)
FROM
tests;
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Formatting MySQL TIME values
Although MySQL uses 'HH:MM:SS' when retrieving and displaying the a TIME value, you can display the TIME value in your preferred way using the TIME_FORMAT function.
The TIME_FORMAT function is like the DATE_FORMAT function except that the TIME_FORMAT function is used to format a TIME value only.
See the following example.
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SELECT
name,
TIME_FORMAT(start_at, '%h:%i %p') start_at,
TIME_FORMAT(end_at, '%h:%i %p') end_at
FROM
tests;
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In the time format string above:
-
%hmeans two-digit hours from 0 to 12. -
%imeans two-digit minutes from 0 to 60. -
%pmeans AM or PM.
Extracting hour, minute, and second from a TIME value
To extract the hour, minute, and second from a TIME value, you use HOUR, MINUTE, and SECONDfunctions as follows:
Getting UTC time value
To get the UTC time, you use UTC_TIME function as follows:
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SELECT
CURRENT_TIME(),
UTC_TIME();
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In this tutorial, we have been covered a lot about MySQL TIME data type and some commonly used temporal functions for manipulating TIME values.