How to Format Dates and Times in SQL: A Comprehensive Tutorial.
Handling databases means dealing with dates and times in SQL. Correct formatting of dates and times might be useful in handling data records properly and also make reports more readable. The following blog post outlines the common SQL date and time formatting techniques such that you end up with an excellent understanding of how you manipulate these kinds of data.
1. SQL Date and Time Data Types
SQL provides the following date and time data types that can be used. Doubtless, the most commonly known are:
DATE: The date type of data that has only date values, in YYYY-MM-DD format.
TIME: This type of data stores only time values, in HH:MI:SS format.
DATETIME: This type of data stores both date and time values, in YYYY-MM-DD HH:MI:SS format.
TIMESTAMP: This is similar to DATETIME, but offers even more precision.
INTERVAL: This is used for storing a period of time, such as days, months, or years.
Depending on the SQL database, these data types vary slightly, but the idea is the same.
2. Formatting Dates in SQL
We can output the dates in a wide variety of formats using the MySQL DATE_FORMAT function, the Oracle TO_CHAR function, and more across other databases. Here's how we do it:
MySQL Example
For example, in MySQL, you might use the DATE_FORMAT() function for custom date output like this:
SELECT DATE_FORMAT(order_date, '%Y-%m-%d') AS formatted_date FROM orders;
%Y - Year (4 digits)
%y - Year (2 digits)
%m - Month (01-12)
%d - Day of the month (01-31)
%b - Abbreviated month name (Jan-Dec)
%W - Full weekday name (Sunday-Saturday)
Example:
SELECT DATE_FORMAT(order_date, '%W, %M %d, %Y') AS formatted_date FROM orders;
Would return dates in the format "Sunday, January 01, 2023".
SQL Server Example
You can use either the FORMAT function or the CONVERT function in SQL Server.
SELECT FORMAT(order_date, 'yyyy-MM-dd') AS formatted_date FROM orders;
Or use CONVERT:
SELECT CONVERT(varchar, order_date, 23) AS formatted_date FROM orders;
Oracle Example
In Oracle, the TO_CHAR function is often utilized:
SELECT TO_CHAR(order_date, 'YYYY-MM-DD') AS formatted_date FROM orders;
Oracle TO_CHAR Format Specifiers:
YYYY - 4-digit year
MM - 2-digit month
DD - 2-digit day of the month
DY - Abbreviated weekday name (Sun-Sat)
There are no end
This would display times in a 12-hour format, for example, 03:30 PM.
SQL Server Example
In SQL Server, you can also use the FORMAT function with times:
SELECT FORMAT(start_time, 'hh:mm tt') AS formatted_time FROM events;
This example also returns time as a 12-hour time with AM/PM notation.
Oracle Example
In Oracle, you use TO_CHAR:
SELECT TO_CHAR(start_time, 'HH:MI AM') AS formatted_time FROM events;
Oracle TO_CHAR Format Specifiers for Time:
HH - Hour (12-hour format)
MI - Minutes
SS - Seconds
AM or PM - Meridian indicator
4. Time Zones and SQL
Time zones are necessary in dealing with international applications. SQL databases usually support time zones in some form.
MySQL
Utilizing MySQL you can utilize the CONVERT_TZ function to convert a date/time field to a different time zone:sql
SELECT order_date FROM orders CONVERT_TZ('UTC', 'America/New_York') AS new_york_time;
Oracle's FROM_TZ and AT TIME ZONE functions enable time zone conversion:
SELECT FROM_TZ(order_date, 'UTC') AT TIME ZONE 'America/New_York' AS est_time FROM orders;
5. Formatting Date Intervals and Arithmetic
Date intervals permit calculation of dates' differences and adding/removing time units.
MySQL Example
SELECT order_date + INTERVAL 7 DAY AS next_week FROM orders;
SQL Server Example
In SQL Server, use the DATEADD function:
SELECT DATEADD(day, 7, order_date) AS next_week FROM orders;
Oracle Example
Oracle enables you to use INTERVAL:
SELECT order_date + INTERVAL '7' DAY AS next_week FROM orders;
6. Practical Examples and Use Cases
Example 1: Formatting Birth Dates in a Readable Format
Suppose you want to show the birth dates of customers in an understandable format:
SELECT customer_name, DATE_FORMAT(birth_date, '%M %d, %Y') AS formatted_birthdate FROM customers;
Example 2: Calculating Age from Birth Dates
To get the age of a person from their date of birth in years:
SELECT customer_name, YEAR(CURDATE()) - YEAR(birth_date) AS age FROM customers;
7. Final Advice about Working with Dates and Times in SQL
1. Date functions are implemented differently so use your database documentation to verify those functions.
2. Store Dates in UTC When Possible: In applications spanning the globe, there's simply no getting around time zones. Use a universal time format like UTC to remove confusion.
3. Standardize Formats: Most importantly, when you are writing logs and audit material, try to use standard formats as often as possible.
Conclusion
Formatting dates and times in SQL Formatting dates and times in SQL is important to your data's readability and consistency. SQL has a wide set of powerful tools to help you manage and display dates according to your application's needs: DATE_FORMAT, TO_CHAR, FORMAT, and CONVERT are a few examples. The techniques learned apply regardless of whether you are working with MySQL, SQL Server, or Oracle.
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