DATE

Understanding the DATEDIFF SQL Function: A Comprehensive Guide

intro

One of the crucial SQL functions that aid in time-related data analysis is DATEDIFF. This function allows users to calculate the difference between two dates, providing critical insights and aiding in efficient data management. In this article, you’ll delve deep into the DATEDIFF function, exploring its usage, and how it varies across popular DBMSs.

Tools used in the tutorial
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Dbvisualizer DBVISUALIZER
TOP RATED DATABASE MANAGEMENT TOOL AND SQL CLIENT

What Is DATEDIFF in SQL?

DATEDIFF is a function in SQL that calculates the difference between two date or time expressions. This function is widely used in various industries to track durations, calculate age, find tenure, and perform numerous other time-related calculations.

The general syntax of the DATEDIFF function is:

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1 DATEDIFF (datepart, startdate, enddate)
  • datepart: The units in which the function reports the difference between startdate and enddate (e.g., year, month, day, etc.).
  • startdate and enddate: The two dates you want to calculate the difference between.

Note that in some DBMSs, datepart is fixed (e.g., always days, months, …) and the syntax of DATEDIFF becomes:

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1 DATEDIFF(startdate, enddate)

How to Use DATEDIFF in SQL

Using DATEDIFF is straightforward. Here is a step-by-step guide to help you understand how to adopt this function.

1. Choose the Date Part

First, decide which part of the date you want to calculate the difference for. This could be years, months, days, etc.

2. Specify the Start and End Dates

Next, provide the two dates you want to compare. Ensure that the date format is consistent and recognized by your DBMS.

3. Run the Query

Execute the query to get the difference between the two dates.

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1 SELECT DATEDIFF(year, '2023-01-01', '2024-01-01') AS YearDifference;

Execute the query in a fully-featured database client:

Running the query in DbVisualizer
Running the query in DbVisualizer

As you can see, the query will return "1," which means there is a one-year difference between the two dates.

Differences of the DATEDIFF SQL function in Popular Databases

Understanding how DATEDIFF works across different databases is crucial for ensuring consistent and accurate date and time calculations in diverse data management systems.

Here’s how the function, or its equivalent, is implemented in 20 popular databases.

1. MySQL

In MySQL, the DATEDIFF function calculates the difference in days between two dates.

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1 SELECT DATEDIFF('2023-01-01', '2022-01-01') AS DateDifference; -- Returns 365

2. Microsoft SQL Server

SQL Server provides more flexibility, allowing users to specify the date part. The DATEDIFF syntax is slightly different, and it also considers the time part if provided.

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1 SELECT DATEDIFF(year, '2022-01-01', '2023-01-01T01:00:00') AS DateDifference; -- Returns 1

3. MariaDB

The MariaDB DATEDIFF function behaves similarly to MySQL, calculating the difference in days.

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1 SELECT DATEDIFF('2023-01-01', '2022-01-01') AS DateDifference; -- Returns 365

4. Google BigQuery

BigQuery uses the DATE_DIFF function to calculate the difference between dates, requiring the date part as an argument.

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1 SELECT DATE_DIFF(DATE '2023-01-01', DATE '2022-01-01', DAY) AS DateDifference; -- Returns 365

5. Snowflake

In Snowflake, you can use the DATEDIFF function and specify the date part you want to compare.

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1 SELECT DATEDIFF('day', '2022-01-01', '2023-01-01') AS DateDifference; -- Returns 365

6. Amazon Redshift

The Redshift DATEDIFF function is similar to that of MySQL and MariaDB, providing the difference in days.

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1 SELECT DATEDIFF(day, '2022-01-01', '2023-01-01') AS DateDifference; -- Returns 365

7. Apache Hive

The Apache Hive DATEDIFF function calculates the difference in days between two dates.

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1 SELECT DATEDIFF('2023-01-01', '2022-01-01') AS DateDifference; -- Returns 365

8. Sybase

The Sybase DATEDIFF function is versatile, allowing users to specify the date part they want to compare.

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1 SELECT DATEDIFF(day, '2022-01-01', '2023-01-01') AS DateDifference; -- Returns 365

9. CockroachDB

The CockroachDB DATEDIFF function calculates the difference in the specified date part.

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1 SELECT DATEDIFF('day', '2022-01-01', '2023-01-01') AS DateDifference; -- Returns 365

Databases Without the DATEDIFF SQL Function: How to Achieve the Same Thing

Let’s see the most popular databases that do not offer a direct implementation of DATEDIFF but allow you to achieve the same result with some workarounds.

1. PostgreSQL

PostgreSQL does not have a DATEDIFF function, but you can use "AGE" to achieve a similar result.

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1 SELECT AGE('2023-01-01', '2022-01-01'); -- Returns 1 year

2. Oracle

Oracle Database does not use DATEDIFF, but you can use "MONTHS_BETWEEN" to find the difference in months.

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1 SELECT MONTHS_BETWEEN('2023-01-01', '2022-01-01') FROM dual; -- Returns 12

3. SQLite

SQLite allows direct date subtraction, and you can use "strftime" to extract specific date parts.

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1 SELECT strftime('%Y', '2023-01-01') - strftime('%Y', '2022-01-01') AS YearDifference; -- Returns 1

4. IBM Db2

IBM Db2 has a specific function named "MONTHS_BETWEEN" to calculate the difference in months.

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1 SELECT MONTHS_BETWEEN('2023-01-01', '2022-01-01') 2 FROM sysibm.sysdummy1; -- Returns 12

5. SAP HANA

SAP HANA provides the DAYS_BETWEEN function for calculating the difference in days.

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1 SELECT DAYS_BETWEEN(TO_DATE('2023-01-01'), TO_DATE('2022-01-01')) FROM DUMMY; -- Returns 365

6. Teradata

In Teradata, you can subtract DATE objects directly to get the difference in days.

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1 SELECT (DATE '2023-01-01' - DATE '2022-01-01') AS DateDifference; -- Returns 365

7. Informix

Informix allows for direct subtraction of dates to calculate the difference in days using the TO_DATE function.

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1 SELECT (TO_DATE('2023-01-01', "%Y-%m-%d") - TO_DATE('2022-01-01', "%Y-%m-%d")) AS DateDifference FROM syst

Conclusion: Using the DATEDIFF SQL function

The DATEDIFF SQL function is really helpful when you work with dates in databases, as it helps you find out the difference between two dates. Different databases like MySQL, SQL Server, and PostgreSQL have their own ways of using this function, which means you need to know how it works in each one to get the results you want.

Using SQL editors like DbVisualizer that understand these differences can make your work a lot easier. They help you write your queries correctly, show you when there’s a mistake, and work well with many types of databases. So, learning how to use DATEDIFF properly and choosing a good SQL editor are important steps to handle date-related tasks effectively in databases.

Frequently Asked Questions (FAQs)

1. What is the DATEDIFF function used for?

The DATEDIFF function is used to calculate the difference between two dates, typically resulting in a number representing the time interval between those dates.

2. Do all databases support the DATEDIFF function?

Most relational databases support a version of the DATEDIFF function, but the syntax and usage might differ. Some databases might have alternative functions or methods to achieve the same result.

3. Can I calculate the difference in units other than days with DATEDIFF?

Yes, many databases allow you to specify the time unit for the result, such as years, months, days, hours, minutes, and seconds.

4. Is there a standard syntax for the DATEDIFF function across all databases?

No, the syntax for the DATEDIFF SQL function can vary significantly between different databases. You can find the basic differences in this article and for more info please refer to the specific documentation for the database you are using.

5. Are there SQL editors that can help me write the correct DATEDIFF syntax for different databases?

Yes, there are advanced SQL editors and Integrated Development Environments (IDEs) that provide features like syntax highlighting, auto-completion, and error checking, which can help ensure that you are using the correct syntax for your database.

6. Can DATEDIFF work with time values as well as dates?

Yes, some databases allow the DATEDIFF function to calculate the difference based on time values, considering hours, minutes, and seconds in the calculation.

7. What are common mistakes when using the DATEDIFF function?

Common mistakes include using the wrong order of dates (start date and end date), not specifying the correct time unit, and using incorrect syntax for the specific database.

8. Can I use DATEDIFF to calculate age?

Yes, you can use DATEDIFF to calculate age by finding the difference in years between a birthdate and the current date. However, you might need additional calculations to handle months and days for a more accurate age calculation.

9. Does DATEDIFF consider leap years?

Yes, databases that support DATEDIFF typically consider leap years in their calculations, ensuring accurate results.

10. Can DATEDIFF result in a negative number?

Yes, if the end date is earlier than the start date, DATEDIFF will return a negative number. The order of dates matters in the calculation.

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