Hello and welcome to this comprehensive guide on how to convert SQL Server datetime. In the world of programming and database management, datetime is an essential data type that represents dates and times. However, working with datetime can be a bit tricky, especially when it comes to converting it to different formats or manipulating its values. In this article, we will cover everything you need to know about SQL Server datetime conversion, including its syntax, functions, and examples.
Table of Contents
- What is SQL Server Datetime?
- Syntax of SQL Server Datetime Conversion
- SQL Server Datetime Conversion Functions
- Converting SQL Server Datetime to Other Formats
- Common Issues and FAQs
What is SQL Server Datetime?
SQL Server datetime is a data type that stores both date and time information in a single column. It is commonly used in database management systems like Microsoft SQL Server for storing and manipulating time-related data. When working with datetime, it’s important to understand its data structure, which consists of two parts: the date portion and the time portion. The date portion is represented by the number of days since January 1, 1900, while the time portion is represented by the number of seconds past midnight.
Understanding the Data Structure of SQL Server Datetime
The following table shows the date and time portions of SQL Server datetime:
| Date Portion | Time Portion |
|---|---|
| January 1, 1900 = 0 | Midnight = 0 |
| January 2, 1900 = 1 | 1 second past midnight = 1/86400 or 0.000011574 |
| … | … |
For example, the SQL Server datetime value of “2019-10-25 14:30:00” represents October 25, 2019, at 2:30 PM.
Syntax of SQL Server Datetime Conversion
Before we dive into the different methods of converting SQL Server datetime, let’s first take a look at the basic syntax:
CONVERT ( data_type [ ( length ) ], expression [, style ] )
The “CONVERT” function is used to convert a value of one data type to another. In the case of datetime conversion, the data type is usually “datetime” or “datetime2”. The “length” parameter is optional and specifies the maximum length of the output data type. The “expression” parameter is the value that you want to convert, which can be either a datetime value or a string value. The “style” parameter is also optional and determines the format of the output datetime value.
SQL Server Datetime Conversion Functions
There are several built-in functions in SQL Server that you can use to convert datetime values to different formats. Here are some of the most commonly used functions:
1. CAST and CONVERT Functions
The CAST and CONVERT functions are used to convert data from one data type to another. When converting datetime, you can use the following syntax:
SELECT CAST(expression AS data_type)
SELECT CONVERT(data_type, expression [, style])
For example, to convert the SQL Server datetime value “2019-10-25 14:30:00” to the format “YYYY-MM-DD”, you can use the following command:
SELECT CONVERT(VARCHAR(10), '2019-10-25 14:30:00', 23)
This will return the string value “2019-10-25”.
2. DATEADD Function
The DATEADD function is used to add or subtract a specified time interval to a datetime value. Here’s the syntax:
DATEADD(interval, number, date)
The “interval” parameter specifies the time interval you want to add or subtract (e.g., days, months, years). The “number” parameter specifies the number of intervals you want to add or subtract. The “date” parameter is the starting datetime value. For example, to add 10 days to the SQL Server datetime value “2019-10-25 14:30:00”, you can use the following command:
SELECT DATEADD(day, 10, '2019-10-25 14:30:00')
This will return the datetime value “2019-11-04 14:30:00”.
3. DATEDIFF Function
The DATEDIFF function is used to calculate the difference between two datetime values in a specified time interval. Here’s the syntax:
DATEDIFF(interval, start_date, end_date)
The “interval” parameter specifies the time interval you want to calculate the difference in (e.g., days, months, years). The “start_date” and “end_date” parameters are the two datetime values that you want to compare. For example, to calculate the number of days between the SQL Server datetime values “2019-10-25 14:30:00” and “2019-11-04 14:30:00”, you can use the following command:
SELECT DATEDIFF(day, '2019-10-25 14:30:00', '2019-11-04 14:30:00')
This will return the integer value 10.
Converting SQL Server Datetime to Other Formats
Now that we’ve covered the basics of SQL Server datetime conversion, let’s take a look at some of the most common datetime formats that you might need to convert to or from.
1. Converting SQL Server Datetime to Unix Timestamp
Unix timestamp is a popular format used in many programming languages and applications, including JavaScript, PHP, and Unix operating systems. It represents the number of seconds that have elapsed since January 1, 1970, 00:00:00 UTC. To convert a SQL Server datetime value to Unix timestamp, you can use the following formula:
DATEDIFF(second, '1970-01-01 00:00:00', your_datetime_value)
For example, to convert the SQL Server datetime value “2019-10-25 14:30:00” to Unix timestamp, you can use the following command:
SELECT DATEDIFF(second, '1970-01-01 00:00:00', '2019-10-25 14:30:00')
This will return the integer value 1572018600.
2. Converting SQL Server Datetime to ISO 8601
ISO 8601 is a widely accepted international standard for representing date and time information. It uses a specific format that includes the year, month, day, hour, minute, and second components, separated by dashes and colons. To convert a SQL Server datetime value to ISO 8601 format, you can use the following command:
SELECT CONVERT(VARCHAR(24), your_datetime_value, 126)
For example, to convert the SQL Server datetime value “2019-10-25 14:30:00” to ISO 8601 format, you can use the following command:
SELECT CONVERT(VARCHAR(24), '2019-10-25 14:30:00', 126)
This will return the string value “2019-10-25T14:30:00”.
Common Issues and FAQs
1. How can I convert a string value to SQL Server datetime?
To convert a string value to SQL Server datetime, you can use the CONVERT function with the appropriate style code. For example, to convert the string value “10/25/2019 14:30:00” to SQL Server datetime, you can use the following command:
SELECT CONVERT(datetime, '10/25/2019 14:30:00', 101)
This will return the SQL Server datetime value “2019-10-25 14:30:00”.
2. How can I convert SQL Server datetime to Eastern Standard Time?
To convert a SQL Server datetime value to Eastern Standard Time, you can use the DATEADD function to add or subtract the appropriate number of hours. For example, to convert the SQL Server datetime value “2019-10-25 14:30:00” to Eastern Standard Time, you can use the following command:
SELECT DATEADD(hour, -4, '2019-10-25 14:30:00')
This will return the datetime value “2019-10-25 10:30:00”.
3. How can I convert SQL Server datetime to epoch time?
To convert a SQL Server datetime value to epoch time, which is the number of seconds that have elapsed since January 1, 1970, 00:00:00 UTC, you can use the DATEDIFF function with the appropriate time interval. For example, to convert the SQL Server datetime value “2019-10-25 14:30:00” to epoch time, you can use the following command:
SELECT DATEDIFF(second, '1970-01-01 00:00:00', '2019-10-25 14:30:00')
This will return the integer value 1572018600.
4. How can I convert SQL Server datetime to UTC?
To convert a SQL Server datetime value to UTC (Coordinated Universal Time), you can use the DATEADD function to add or subtract the appropriate number of hours. For example, to convert the SQL Server datetime value “2019-10-25 14:30:00” to UTC, you can use the following command:
SELECT DATEADD(hour, -5, '2019-10-25 14:30:00')
This will return the datetime value “2019-10-25 19:30:00”.
5. How can I format SQL Server datetime in a specific way?
To format SQL Server datetime in a specific way, you can use the CONVERT function with the appropriate style code. The following table shows some of the most commonly used style codes:
| Style Code | Output Format |
|---|---|
| 101 | mm/dd/yyyy |
| 102 | yyyy.mm.dd |
| 103 | dd/mm/yyyy |
| 104 | dd.mm.yyyy |
| 105 | dd-mm-yyyy |
| 106 | dd mon yyyy |
| 107 | mon dd, yyyy |
| 108 | hh:mi:ss |
| 109 | mon dd yyyy hh:mi:ss:mmmAM (or PM) |
| 110 | mm-dd-yyyy |
| 111 | yyyy/mm/dd |
| 112 | yyyymmdd |
| 120 | yyyy-mm-dd hh:mi:ss |
| 121 | yyyy-mm-dd hh:mi:ss.mmm |
| 126 | yyyy-mm-ddThh:mi:ss.mmm |
For example, to convert the SQL Server datetime value “2019-10-25 14:30:00” to the format “YYYY/MM/DD”, you can use the following command:
SELECT CONVERT(VARCHAR(10), '2019-10-25 14:30:00', 111)
This will return the string value “2019/10/25”.
Congratulations! You have learned how to convert SQL Server datetime values to different formats.