Author: Ian

MySQL DATEDIFF() vs TIMEDIFF(): What’s the Difference?

Posted on by Ian

Two date functions included in MySQL are DATEDIFF() and TIMEDIFF().

Both functions do a similar thing, but with some meaningful differences.

The following table summarizes the difference between these two functions:

DATEDIFF() TIMEDIFF()
Result is expressed as a value in days. Result is expressed as a time value.
Compares only the date value of its arguments. Compares the time value of its arguments.
Accepts date or date-and-time expressions. Accepts time or date-and-time expressions.
Both arguments can be of a different type (date or date-and-time). Both arguments must be the same type (either time or date-and-time).

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DATEDIFF() vs DATEDIFF_BIG() in SQL Server: What’s the Difference?

Posted on by Ian

If you’ve ever needed to find the difference between two dates in SQL Server, you might have used the DATEDIFF() function. This function returns the amount of time between two dates using a datepart specified by you. For example, you could use it to return the number of days between date 1 and date 2. You can also get it to return the number of minutes, seconds, months, years, etc.

The DATEDIFF_BIG() function works exactly the same way, but with one subtle difference: Its return data type.

So the difference between these two functions is the data type of their return value.

  • DATEDIFF() returns a signed integer (int)
  • DATEDIFF_BIG() returns a signed big integer (bigint)

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What is the Year 2038 Problem?

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The Year 2038 problem (also referred to as the Y2K38 bug) refers to a problem that some computer systems might encounter when dealing with times past 2038-01-19 03:14:07.

Many computer systems, such as Unix and Unix-based systems, don’t calculate time using the Gregorian calendar. They calculate time as the number of seconds since 1 January 1970. Therefore, in these systems, time is represented as a big number (i.e. the number of seconds passed since 1970-01-01 00:00:00). This is typically referred to as Epoch time, Unix time, Unix Epoch time, or POSIX time. As I write this, Unix time is 1560913841. And as I write this next line, Unix time has incremented to 1560913879.

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How to Return the Unix Timestamp in SQL Server (T-SQL)

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You might have noticed that SQL Server doesn’t have an equivalent of MySQL‘s UNIX_TIMESTAMP() function.

However, it’s not that difficult to return the Unix timestamp in SQL Server.

The Unix timestamp (also known as Unix Epoch time, Unix time, or POSIX time) is simply the number of seconds that have elapsed since 00:00:00 Thursday, 1 January 1970, Coordinated Universal Time (UTC). Therefore, in SQL Server we can use a couple of T-SQL functions to return this.

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Examples of Converting ‘time’ to ‘datetime’ in SQL Server (T-SQL)

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This article contains examples of converting a time value to a datetime value in SQL Server.

When you convert a time value to datetime, extra information is added to the value. This is because the datetime data type contains both date and time information. The time data type, on the other hand, only contains time information. Therefore, date information is added to the value when you perform such a conversion. Specifically, the date is set to ‘1900-01-01’.

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Examples of Converting ‘date’ to ‘datetimeoffset’ in SQL Server (T-SQL)

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This article contains examples of converting a date value to a datetimeoffset value in SQL Server.

When you convert a date value to datetimeoffset, extra information is added to the value. This is because the datetimeoffset data type contains both date and time information, as well as the time offset information. In other words, the datetimeoffset data type defines a date that is combined with a time of a day that has time zone awareness and is based on a 24-hour clock. The date data type, on the other hand, only contains date information.

When we convert from date to datetimeoffset, the time (and time zone offset) is automatically added to the value. However, you can always change the value if required (including the time zone offset).

The datetimeoffset data type also allows you to specify the fractional seconds precision. If you don’t specify this, it uses a scale of 7. This means it will include 7 digits on the right side of the decimal point.

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Examples of Converting ‘date’ to ‘smalldatetime’ in SQL Server (T-SQL)

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This article contains examples of converting a date value to a smalldatetime value in SQL Server.

When you convert a date value to smalldatetime, extra information is added to the value. This is because the smalldatetime data type contains both date and time information. The date data type, on the other hand, only contains date information.

However, there are cases where a date to smalldatetime conversion might fail. In particular, if the date value is outside the range supported by smalldatetime then it will fail with an error.

In any case, below are examples of converting between these two data types.

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Examples of Converting ‘date’ to ‘datetime2’ in SQL Server (T-SQL)

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This article contains examples of converting a date value to a datetime2 value in SQL Server.

When you convert a date value to datetime2, extra information is added to the value. This is because the datetime2 data type contains both date and time information. The date data type, on the other hand, only contains date information.

The datetime2 data type is basically an extension of the datetime data type. It has a larger date range, a larger default fractional precision, and optional user-specified precision.

In any case, the conversion process is exactly the same regardless of the data type. The only difference is the amount of information that’s available between date, datetime and datetime2.

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Examples of Converting ‘date’ to ‘datetime’ in SQL Server (T-SQL)

Posted on by Ian

This article contains examples of converting a date value to a datetime value in SQL Server.

When you convert a date value to datetime, extra information is added to the value. This is because the datetime data type contains both date and time information. The date data type, on the other hand, only contains date information.

Continue reading →