Conversion Errors: Solving Date and Time Format Issues

There’s always a struggle when dates and times don’t appear in the required format or when query outputs fail to meet viewers’ needs. Fortunately, SQL Server provides built-in features to format date strings according to your preferences. However, in order to avoid conversion errors and ensure successful interpretation by SQL Server, it’s crucial to provide the input in the correct format. Let’s take a closer look at the common error message: “Conversion failed when converting date and/or time from character string.”

date time conversion error
Figure 1: Date and/or time conversion error from the character string

The Potential Causes

This error usually occurs when the date literal is incorrect and cannot be converted from the string into DateTime or date formats. Let’s explore some of the reasons behind this issue and discuss the appropriate solutions.

Example 1: United Kingdom Date and Time Format

In the United Kingdom, dates are commonly displayed in the day-month-year format (e.g., January 10, 2015 or 10/1/2015). To achieve this format using SQL Server’s built-in “convert” function, we can use formatting style 103.

In the following example, we can observe that the provided date string is in the wrong format. It presents the month first, followed by the day and year. This format cannot be interpreted by SQL Server, resulting in an error. The correct format for UK-style date conversion using the “103” date style is “dd/mm/yyyy.”

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Wrong Format:

DECLARE @date_time_value VARCHAR(100)='10/16/2015 21:02:04'
SELECT CONVERT(datetime2, @date_time_value, 103) AS UK_Date_Time_Style

‘Conversion failed when converting date and time’ [Error Solved]
Figure 2: Wrong Date Format resulting in an error

Correct Format:

DECLARE @date_time_value VARCHAR(100)='10/1/15 21:02:04'
SELECT CONVERT(datetime2, @date_time_value, 103) AS Date_Time_Style

‘Conversion failed when converting date and time’ [Error Solved]
Figure 3: Correct Date Format with “dd/mm/yyyy” British/French date style

DECLARE @date_time_value VARCHAR(100)='10/1/15 21:02:04'
SELECT CONVERT(datetime2, @date_time_value, 3) AS UK_Date_Time_Style

‘Conversion failed when converting date and time’ [Error Solved]
Figure 4: Correct Date Format with “dd/mm/yy” British/French date style

Example 2: Handling Invalid Dates

Sometimes, string-to-date conversion in SQL Server fails not because of date or time format issues, but because you’re trying to store incorrect information that is not acceptable to the schema.

Wrong Date:
The following error occurs because “29 February” does not exist in the year 2019, as it is not a leap year.

DECLARE @date_time_value VARCHAR(100)='2019-02-29 21:02:04'
SELECT CAST(@date_time_value AS datetime2) AS date_time_value

‘Conversion failed when converting date and time’ [Error Solved]
Figure 5: Error raised as 2019 is not a leap year, so it does not have 29 Feb as date

Correct Date:
To avoid this error, use a valid date such as “2019-02-28 21:02:04”.

DECLARE @date_time_value VARCHAR(100)='2019-02-28 21:02:04'
SELECT CAST(@date_time_value AS datetime2) AS date_time_value

‘Conversion failed when converting date and time’ [Error Solved]
Figure 6: Correct date

ISO 8601 Date Format: A Universal Solution

While multiple date formats are available for manipulating date values, choosing a datetime representation can become challenging when working with a global audience. Culture-specific date/time literals should be avoided in such cases. For example, the date “03/08/2018” can be interpreted differently in various regions of the world:

  • In the UK style, it is interpreted as “8th of March 2018.”
  • In the European style, it is interpreted as “3rd of August 2018.”

Thankfully, the international date format established by ISO 8601 provides one solution. The global standard format “YYYY-MM-DDThh:mm:ss” is more language-independent and addresses these issues. Here, “yyyy” represents the year, “mm” represents the month, and “dd” represents the day. Therefore, the date “8th of March 2018” in the international ISO format is written as “2018-03-08”. Utilizing the ISO format is the best choice for date representation.

DECLARE @date_time_value VARCHAR(100)='2019-03-28 21:02:04'
SELECT CONVERT(datetime2, @date_time_value, 126) AS [yyyy-mm-ddThh:mi:ss.mmm]

‘Conversion failed when converting date and time’ [Error Solved]
Figure 7: International Standard ISO 8601 date format

Recommendations

This article aimed to alleviate the confusion frequently encountered in the community regarding date/time values. It’s highly recommended to store dates in appropriate data types such as DATE, DATETIME, and preferably DATETIME2 (which provides more precision). Leave the date information formatting to the user interface layer instead of retrieving it from the database.

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