Doing Time Guide

Date and Time Handling Guide

This guide covers effective ways to work with date and time information in MariaDB. Learn about temporal data types, essential functions for recording current date/time, extracting specific parts, and formatting your date/time values for display or analysis.

Temporal Data Types

While dates and times can be stored as character strings, using specific temporal data types allows you to leverage MariaDB's built-in functions for manipulation and formatting.

• DATE: For dates only. Format: YYYY-MM-DD.

• TIME: For time only. Format: HHH:MM:SS (hours can range beyond 24).

• DATETIME: For combined date and time. Format: YYYY-MM-DD HH:MM:SS.

• TIMESTAMP: Similar to DATETIME, but with a more limited range and automatic update capabilities (not covered here). Range typically from 1970-01-01 00:00:01 UTC to 2038-01-19 03:14:07 UTC. From MariaDB 11.5 (64-bit), this range extends to 2106-02-07.

• YEAR: For years only. Format: YY or YYYY.

Recording Current Date and Time

MariaDB provides several functions to get the current date and time.

Current Date: Use CURRENT_DATE (no parentheses) or CURDATE() (with parentheses).

INSERT INTO billable_work (doctor_id, patient_id, session_date)
VALUES ('1021', '1256', CURRENT_DATE);

To see the ID of the last inserted row (if the primary key is AUTO_INCREMENT):

SELECT rec_id, doctor_id, patient_id, session_date
FROM billable_work
WHERE rec_id = LAST_INSERT_ID();

+--------+-----------+------------+--------------+
| rec_id | doctor_id | patient_id | session_date |
+--------+-----------+------------+--------------+
|   2462 | 1021      | 1256       | 2025-05-28   | -- Example date
+--------+-----------+------------+--------------+

Current Time: Use CURRENT_TIME or CURTIME().

UPDATE billable_work
SET session_time = CURTIME()
WHERE rec_id = '2462';

SELECT patient_id, session_date, session_time
FROM billable_work
WHERE rec_id = '2462';

+------------+--------------+--------------+
| patient_id | session_date | session_time |
+------------+--------------+--------------+
| 1256       | 2025-05-28   | 13:03:22     | -- Example time
+------------+--------------+--------------+

Current Date and Time (Timestamp): Use CURRENT_TIMESTAMP, NOW(), or SYSDATE(). These functions return the current date and time in YYYY-MM-DD HH:MM:SS format, suitable for DATETIME or TIMESTAMP columns.

Extracting Date and Time Parts

Extracting from DATE types:

• YEAR(date_column): Extracts the year.

• MONTH(date_column): Extracts the month number (1-12).

• DAYOFMONTH(date_column): Extracts the day of the month (1-31). Also DAY().

SELECT
    MONTH(session_date) AS Month,
    DAYOFMONTH(session_date) AS Day,
    YEAR(session_date) AS Year
FROM billable_work
WHERE rec_id = '2462';

+-------+------+------+
| Month | Day  | Year |
+-------+------+------+
|     5 |   28 | 2025 | -- Example output
+-------+------+------+

(The AS keyword is used to provide an alias for the output column name.)

Day of the Week:

• DAYOFWEEK(date_column): Returns the weekday index (1=Sunday, 2=Monday, ..., 7=Saturday).

• WEEKDAY(date_column): Returns the weekday index (0=Monday, 1=Tuesday, ..., 6=Sunday).

Example using IF() to determine a billing rate based on the day of the week (Saturday = day 7 for DAYOFWEEK):

SELECT
    patient_id AS 'Patient ID',
    session_date AS 'Date of Session',
    IF(DAYOFWEEK(session_date) = 7, 1.5, 1.0) AS 'Billing Rate'
FROM billable_work
WHERE rec_id = '2462';

The IF(condition, value_if_true, value_if_false) function allows conditional logic.

Other Date Part Functions:

• DAYOFYEAR(date_column): Returns the day of the year (1-366).

• QUARTER(date_column): Returns the quarter of the year (1-4).

Example: Selecting sessions in a specific quarter (e.g., Q2):

SELECT patient_id, session_date
FROM billable_work
WHERE QUARTER(session_date) = 2;

User variables can be used for dynamic queries:

SET @target_quarter := 2;
SELECT patient_id, COUNT(*) AS num_sessions
FROM billable_work
WHERE QUARTER(session_date) = @target_quarter AND doctor_id = '1021'
GROUP BY patient_id;

Extracting from TIME types:

• HOUR(time_column): Extracts the hour.

• MINUTE(time_column): Extracts the minute.

• SECOND(time_column): Extracts the second.

SELECT
    HOUR(session_time) AS Hour,
    MINUTE(session_time) AS Minute,
    SECOND(session_time) AS Second
FROM billable_work
WHERE rec_id = '2462';

+------+--------+--------+
| Hour | Minute | Second |
+------+--------+--------+
|   13 |     03 |     22 | -- Example output
+------+--------+--------+

Using EXTRACT() for DATETIME or TIMESTAMP types: The EXTRACT(unit FROM datetime_column) function extracts a specified unit from a date/time value. Common units: YEAR, MONTH, DAY, HOUR, MINUTE, SECOND. Combined units: YEAR_MONTH, DAY_HOUR, HOUR_MINUTE, etc.

SELECT
    patient_name AS Patient,
    EXTRACT(HOUR FROM appointment) AS Hour,
    EXTRACT(MINUTE FROM appointment) AS Minute
FROM billable_work
JOIN patients ON billable_work.patient_id = patients.patient_id
WHERE doctor_id = '1021'
  AND EXTRACT(MONTH FROM appointment) = 5
  AND EXTRACT(DAY FROM appointment) = 28;

(For details on joining tables, refer to relevant SQL documentation or a guide like "Essential Queries Guide".)

Using a combined unit:

SELECT
    patient_name AS Patient,
    EXTRACT(HOUR_MINUTE FROM appointment) AS AppointmentHM
FROM billable_work
JOIN patients ON billable_work.patient_id = patients.patient_id
WHERE doctor_id = '1021';

Output for HOUR_MINUTE might be like 1303 (for 13:03).

Formatting Dates and Times for Display

Wordier Date Formats:

• MONTHNAME(date_column): Returns the full name of the month (e.g., 'May').

• DAYNAME(date_column): Returns the full name of the day (e.g., 'Wednesday').

Example using CONCAT() to combine parts:

SELECT
    patient_name AS Patient,
    CONCAT(
        DAYNAME(appointment), ' - ',
        MONTHNAME(appointment), ' ',
        DAYOFMONTH(appointment), ', ',
        YEAR(appointment)
    ) AS Appointment
FROM billable_work
JOIN patients ON billable_work.patient_id = patients.patient_id
WHERE doctor_id = '1021' AND DATE(appointment) = '2025-05-28'
LIMIT 1;

+-------------------+------------------------------+
| Patient           | Appointment                  |
+-------------------+------------------------------+
| Michael Zabalaoui | Wednesday - May 28, 2025     | -- Example
+-------------------+------------------------------+

Using DATE_FORMAT(datetime_column, format_string): This function provides extensive formatting options. Syntax: DATE_FORMAT(date_value, 'format_options_and_literals').

SELECT
    patient_name AS Patient,
    DATE_FORMAT(appointment, '%W - %M %e, %Y') AS Appointment
FROM billable_work
JOIN patients ON billable_work.patient_id = patients.patient_id
WHERE doctor_id = '1021' AND DATE_FORMAT(appointment, '%c') = 5 -- Filter by month 5 (May)
LIMIT 1;

Common format specifiers:

• %W: Full weekday name

• %M: Full month name

• %e: Day of the month, numeric (1-31)

• %d: Day of the month, 2 digits (01-31)

• %Y: Year, 4 digits

• %y: Year, 2 digits

• %c: Month, numeric (1-12)

• %r: Time in 12-hour format (hh:mm:ss AM/PM)

• %T: Time in 24-hour format (hh:mm:ss)

• %H: Hour (00-23)

• %h or %I: Hour (01-12)

• %i: Minutes (00-59)

• %s or %S: Seconds (00-59)

• %p: AM or PM

Example with time:

SELECT
    DATE_FORMAT(appointment, '%W - %M %e, %Y at %r') AS Appointment
FROM billable_work
LIMIT 1;

+-------------------------------------------------+
| Appointment                                     |
+-------------------------------------------------+
| Wednesday - May 28, 2025 at 01:03:22 PM         | -- Example
+-------------------------------------------------+

For a complete list of options, see the official DATE_FORMAT() documentation.

Using TIME_FORMAT(time_column, format_string): Similar to DATE_FORMAT(), but uses only time-related format options.

SELECT
    patient_name AS Patient,
    TIME_FORMAT(appointment, '%l:%i %p') AS AppointmentTime
FROM billable_work
JOIN patients ON billable_work.patient_id = patients.patient_id
WHERE doctor_id = '1021'
  AND DATE(appointment) = CURDATE();

+-------------------+-----------------+
| Patient           | AppointmentTime |
+-------------------+-----------------+
| Michael Zabalaoui |     1:03 PM     | -- Example
+-------------------+-----------------+

Here, %l is hour (1-12) and %p adds AM/PM.

Tips for Effective Date/Time Handling

• Use Appropriate Data Types: Choose temporal data types (DATE, TIME, DATETIME, TIMESTAMP, YEAR) over string types for date/time data to leverage built-in functions and ensure data integrity.

• Leverage Built-in Functions: MariaDB offers a rich set of functions for date/time manipulation. Use them within your SQL queries to avoid complex logic in your application code.

• Test Queries: When dealing with complex date/time logic or formatting, test your SQL statements directly in a MariaDB client (like the mariadb command-line tool) to verify results before embedding them in applications.

• Be Aware of Time Zones: TIMESTAMP values are stored in UTC and converted to/from the session's time zone, while DATETIME values are stored "as is" without time zone conversion. Understand how your server and session time zones are configured if working with data across different regions. (Time zone handling is a more advanced topic not fully covered here).

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