Datetimes are a crucial data type in most database-driven applications. Whether you are storing timestamps for financial transactions, log events, or the schedule of a sports team, being able to query and organize this temporal data is essential.

In MySQL, datetime handling is robust with versatile functions and logical operators. But a common task is checking if a datetime value matches, precedes, or follows the current date and time. Constructing efficient and accurate queries relies on picking the right MySQL datetime function and understanding exactly what timestamps they evaluate to.

This comprehensive guide will compare and benchmark MySQL‘s functions for getting the current datetime. You‘ll learn the key technical differences between them, how to best leverage each one, and explore advanced date/time logic through detailed examples. Follow along and you‘ll gain the ability to wrangle dates and times in your applications with flexibility and confidence!

MySQL Datetime Data Types

Before looking at functions, we need to understand the underlying datatypes. MySQL supports a few different formats to store datetimes:

DATE – Stores just the date portion without a time. Takes up 3 bytes.

TIME – Stores just a time without the date. Takes up 3 bytes.

YEAR – Stores a year between 1901-2155. Takes up 1 byte.

DATETIME – Stores date and time. Takes up 8 bytes.

TIMESTAMP – Stores date and time. Takes up 4 bytes. Defaults to the current timestamp when inserted.

For full datetime storage with the date and time, DATETIME and TIMESTAMP are the common options. The main tradeoff is that TIMESTAMP takes half the storage, but DATETIME holds a wider range of dates.

For comparing against the current datetime, we‘ll focus on DATETIME and TIMESTAMP columns using MySQL‘s date functions.

Getting the Current Datetime in MySQL

MySQL provides several functions that return the current date and time which we can then compare against datetime field values:

NOW()
CURRENT_TIMESTAMP
LOCALTIMESTAMP
UTC_TIMESTAMP() 
UNIX_TIMESTAMP()

These all return datetimes, but have subtle differences:

NOW() – Returns the datetime as a string in the YYYY-MM-DD HH:MM:SS format. This matches the internal storage used by DATETIME columns.

CURRENT_TIMESTAMP – A synonym for NOW(). Returns the same value.

LOCALTIMESTAMP – Returns YYYY-MM-DD HH:MM:SS but converts it based on the server‘s configured timezone.

UTC_TIMESTAMP() – Returns the current UTC datetime as a string. Useful for converting datetimes between timezones for coordination.

UNIX_TIMESTAMP() – Returns the number of seconds since the Unix Epoch (Jan 1, 1970) as an integer. This stores datetimes in a machine readable format.

To demonstrate, we can create a table storing event timestamps and compare against the current time:

CREATE TABLE events (
  id INT AUTO_INCREMENT PRIMARY KEY,
  name VARCHAR(50),
  event_time DATETIME
);

INSERT INTO events 
  (name, event_time)
VALUES
  ("Concert", "2025-05-21 20:00:00");

SELECT 
  name, 
  event_time,
  NOW() AS current_datetime,
  event_time >= NOW() AS is_future
FROM events;

This outputs:

+-------------+---------------------+---------------------+----------+
| name        | event_time          | current_datetime    | is_future |
+-------------+---------------------+---------------------+----------+
| Concert     | 2025-05-21 20:00:00 | 2023-03-02 15:44:12 | 1        |  
+-------------+---------------------+---------------------+----------+

By comparing the stored DATETIME value against NOW(), we can easily check if an event is in the past or future.

NOW() vs CURRENT_TIMESTAMP

As mentioned earlier, NOW() and CURRENT_TIMESTAMP are synonyms – they return the exact same format and value. CURRENT_TIMESTAMP was added later for improved ANSI SQL compatibility.

So which should you use? The convention in MySQL tends to be NOW() for legacy reasons, but either will work anywhere a current timestamp is needed.

To drive this home, let‘s run both functions in a query:

SELECT 
  NOW() AS now, 
  CURRENT_TIMESTAMP as current_ts, 
  NOW() = CURRENT_TIMESTAMP AS is_equal;

Result:

+---------------------+---------------------+----------+
| now                 | current_ts          | is_equal |  
+---------------------+---------------------+----------+
| 2023-03-02 15:47:32 | 2023-03-02 15:47:32 | 1        |
+---------------------+---------------------+----------+

NOW() vs LOCALTIMESTAMP

The key difference between NOW() and LOCALTIMESTAMP comes down to time zones. NOW() returns the datetime based on the server‘s configured time zone. LOCALTIMESTAMP also respects that timezone, but converts the output to your MySQL client connection‘s time zone.

This allows you to run queries and get localized datetimes even if connecting from across the world.

As an example, setting MySQL and database time zone to US/Pacific:

SET @@global.time_zone = ‘US/Pacific‘;
SET @@session.time_zone = ‘US/Pacific‘;

Querying NOW() and LOCALTIMESTAMP:

SELECT 
  NOW() AS server_tz,
  LOCALTIMESTAMP() AS client_tz;

If your database and client are both in Pacific time, these would match. But for a client in Eastern time:

+---------------------+---------------------+
| server_tz           | client_tz           |
+---------------------+---------------------+    
| 2023-03-02 12:53:18 | 2023-03-02 15:53:18 |
+---------------------+---------------------+

The 3 hour difference reflects the time zone adjustment.

So while NOW() and CURRENT_TIMESTAMP are interchangeable, LOCALTIMESTAMP differs by converting datetimes to your session time zone.

Unix Timestamps with UNIX_TIMESTAMP()

While most MySQL date functions return a formatted string, UNIX_TIMESTAMP() returns an integer count of seconds since the Unix Epoch – January 1st, 1970.

This format is less human readable but makes values easier to order, compare, and calculate intervals with. Timestamps also take up less storage space in integers than verbose strings.

Let‘s take our sample events and show some comparisons:

SELECT
  name,
  event_time,
  UNIX_TIMESTAMP(event_time) AS unix_ts, 
  UNIX_TIMESTAMP() AS current_unix_ts
FROM events; 
+-----------+---------------------+--------------+-------------------+
| name      | event_time          | unix_ts      | current_unix_ts   |
+-----------+---------------------+--------------+-------------------+
| Concert   | 2025-05-21 20:00:00 | 1870918800   | 1677750483        |
+-----------+---------------------+--------------+-------------------+

You can see the event date converts to a future integer timestamp while the current time is a smaller value. This numeric format allows easy relative comparisons.

We can convert integers back into datetimes with FROM_UNIXTIME():

SELECT 
  FROM_UNIXTIME(1870918800) AS datetime; 

+---------------------+
| datetime            |
+---------------------+ 
| 2025-05-21 20:00:00 |  
+---------------------+

Overall UNIX_TIMESTAMP() provides a compact, sortable way to handle datetimes in MySQL suitable for programming and calculation use cases.

Comparing Datetimes to Now

Once we understand the available MySQL functions to access the current date and time, the next step is comparing them against stored DATETIME/TIMESTAMP values.

The main logical operators are:

=    (Equal)
<=> (Null-safe equal)    
!=   (Not equal)
>    (Greater than)
<    (Less than)   
>=  (Greater than or equal)
<=  (Less than or equal)

Which should you use? It depends on whether you want to match exact points in time, or ranges before/after.

Matching exact seconds is difficult due to tiny time deltas. Typically a range is more practical for cases like "is this datetime in the past or future"?

Let‘s explore some examples of comparing events to Now() in useful ways:

Events Happening Today

Finding events happening today filters for those where the date portion matches today‘s date. This ignores mismatches in the time portion.

SELECT 
   name, event_time
FROM
   events
WHERE
   DATE(event_time) = CURRENT_DATE;

DATE(event_time) extracts just the date out of the datetime. Comparing the dates allows a range match.

Another approach is comparing that the datetime falls within the bounds of today‘s date as the minimum, and tomorrow as the maximum:

SELECT
  name, event_time  
FROM
  events
WHERE 
  event_time >= CURRENT_DATE
  AND event_time < CURRENT_DATE + INTERVAL 1 DAY;

Here we build in a 1 day interval to get tomorrow‘s date as the upper cutoff. Very powerful for matching ranges!

Events Within the Past Week

We can also look back or forward in time using intervals. To find events within the last week: 

SELECT
   name, event_time
FROM
   events  
WHERE
   event_time >= NOW() - INTERVAL 1 WEEK;

The interval arithmetic lets us deduct 1 week from the current time and check if event times fall after that threshold.

Intervals can also use other units like hours, minutes, seconds, days, months etc. This flexibility helps slice datetimes in many ways.

Events After Now()

A very common need is querying for future dated events. We can filter down using the > or >= operators:

SELECT 
   name, event_time
FROM
   events
WHERE
   event_time > NOW();

This returns events with a datetime greater than the current NOW() value.

Using >= would return exact datetime matches too.

Event Status Compared to Now()

In many scenarios we want to categorize events based on their position relative to the current datetime. Are they expired, active/current, or upcoming?

Here‘s an example query that adds a status column:

SELECT
  name,
  event_time,
  CASE 
    WHEN event_time < NOW() THEN ‘Expired‘
    WHEN event_time >= NOW() AND event_time < NOW() + INTERVAL 1 MONTH THEN ‘Current‘     
    WHEN event_time >= NOW() + INTERVAL 1 MONTH THEN ‘Upcoming‘  
  END AS status
FROM 
  events;

By using CASE logic that checks different datetime conditions, we can easily tag records with a readable status. The end result is:

+----------------+---------------------+-----------+
| name           | event_time          | status    |
+----------------+---------------------+-----------+
| Balloon Fest   | 2022-06-15 12:00:00 | Expired   |
| State Fair     | 2022-08-30 10:00:00 | Current   |  
| Air Show       | 2022-11-13 13:00:00 | Upcoming  |   
+----------------+---------------------+-----------+

Categorizing records relative to NOW() makes for very powerful reporting queries!

Handling Null Datetimes

A subtle issue that can trip you up is comparing datetimes against NULL values. Standard comparison operators like <> and >= will always return NULL rather than TRUE/FALSE if either side is NULL.

For example:

SELECT 
   name, 
   event_time >= NOW() AS is_future
FROM
   events
WHERE
   event_time IS NULL;

You would expect true/false values for is_future. But instead every row returns NULL despite the WHERE clause filtering.

To work around this, the <=> operator can be used for NULL-safe comparisons that handles NULLs:

SELECT
   name, 
   event_time <=> NOW() AS is_now
FROM 
   events
WHERE
   event_time IS NULL;

Now we correctly get is_now = 0 for false, rather than all NULLs.

In practice, to allow datetimes to be NULL:

SELECT 
   name, 
   event_time
FROM
   events
WHERE 
   event_time <=> NOW() OR event_time IS NULL;

This will check for matching times, and allow NULLs through. The NULL-safe logic helps accurately match on nullable columns.

Optimizing Datetime Queries

When querying against large datetime columns, performance can slow down without proper database indexes. Examine this simplified events table:

CREATE TABLE events (
  id INT PRIMARY KEY,
  name VARCHAR(50),
  event_time DATETIME
);

INSERT INTO events (name, event_time) 
  VALUES (‘Conference‘, NOW());

With no indexes except the primary key, this query:

SELECT * 
FROM events
WHERE event_time > NOW() - INTERVAL 7 DAY;

Requires a full table scan of every row to evaluate the datetime condition, costing significant time as data grows.

Adding an index optimizes this:

CREATE INDEX idx_event_time ON events(event_time);

Now the database can immediately narrow its search down to relevant rows ordered by event_time. Index columns should be declared whenever datetime comparisons will be made.

For even faster lookups, the indexed column(s) can use TIMESTAMP instead of DATETIME – its compact size improves performance.

Properly indexing your time and date fields is crucial for fast queries as database size increases!

Best Practices Summary

Working with datetimes in MySQL is very flexible with a variety of data types and functions. Here are some key guidelines:

  • Use DATETIME for wide date ranges or DECIMAL storage. But TIMESTAMP for optimal performance.
  • Normalize datetimes to UTC, then convert with LOCALTIMESTAMP as needed.
  • Index columns made in WHERE datetime clauses for big speed boosts.
  • Be aware that NOW() vs LOCALTIMESTAMP can differ in session time zones.
  • UNIX_TIMESTAMP() converts to/from integer storage for calculations.
  • Handle NULL through IS NULL checks and <=> for NULL-safe comparisons.
  • Calculate datetimes offsets using INTERVAL unit arithmetic.

Datetimes power most applications. Whether you are building analytical dashboards, scheduling services, or tracking data science experiments over time, honing MySQL date abilities is essential.

I hope these extensive examples give you new datetime confidence and mastery! Now integrate this knowledge into your own information systems and extract value at scale.

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