mssql

Understanding ‘datetime2’ Storage Size in SQL Server

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In this article I share some observations I’ve had regarding the datetime2 data type’s storage size in SQL Server. Perhaps I will clarify some points about the actual storage size used by this data type when stored in a database.

In particular, I look at the following:

  • Microsoft’s documentation
  • Data stored in a variable
    • Length in bytes using DATALENGTH()
    • Length in bytes using DATALENGTH() after converting to varbinary
  • Data stored in a database
    • Length in bytes using COL_LENGTH()
    • Length in bytes using DBCC PAGE()

Some of those seem to contradict each other, and you will see two different storage size amounts for the same value, depending on where you look.

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Converting Between Date & Time Data Types in SQL Server (T-SQL Examples)

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When you convert between date and time data types in SQL Server, you need to be mindful of how the new data type will handle the value you’re trying to assign to it.

In some cases you might lose part of the value, in other cases you might gain a bunch of zeros (increasing storage size in the process). You may also end up with a value that’s been rounded up.

The following articles contain examples of conversions between the different date and time data types, with a particular focus on the issues I just mentioned.

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Convert ‘datetimeoffset’ to ‘time’ in SQL Server (T-SQL Examples)

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If you have a datetimeoffset value, but you don’t need the date and time zone offset part, converting it to time will save you a lot of storage space (while removing unnecessary details from the value). This article contains examples of converting a datetimeoffset value to a time value in SQL Server.

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

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If you have a datetimeoffset value, but you don’t need the time and time zone offset part, converting it to date will save you a lot of storage space (while removing unnecessary details from the value). This article contains examples of converting a datetimeoffset value to a date value in SQL Server.

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Convert ‘datetimeoffset’ to ‘smalldatetime’ in SQL Server (T-SQL Examples)

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

When you convert a datetimeoffset value to smalldatetime, the date and hours are copied. The minutes are rounded up (depending on the seconds value) and the seconds are set to 0.

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Convert ‘datetimeoffset’ to ‘datetime2’ in SQL Server (T-SQL Examples)

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

When you convert a datetimeoffset value to datetime2, the date and time are copied to the datetime2 value, and the time zone is truncated. The fractional seconds are also truncated to fit if the destination precision is lower.

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Convert ‘datetimeoffset’ to ‘datetime’ in SQL Server (T-SQL Examples)

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

When you convert a datetimeoffset value to datetime, the date and time values are copied, and the time zone offset is truncated. When the fractional precision of the datetimeoffset value is greater than three digits, the value is truncated.

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

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

One of the benefits of converting a smalldatetime value to date is that you reduce the storage size down from 4 bytes to 3 bytes. However, you do lose the time component from the value, so you would only do this conversion if you don’t need the time.

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