This sheet provides an easy reference to look up limitations and benefits for each SQL Server data type. There are plenty of sql data types to use in SQL Server. Knowing the limitations and benefit of each sql data type will soon pay off.

Benefits example

Choosing the sql data type tinyint instead of int for a "ProductType" column with values ranging from 1 to 10 will save three bytes per record. With 100,000 records you will save 300,000 bytes. That's not much in terms of disc space ("storage is cheap, etc") but you'll probably have indexes containing that column and if that index takes less memory the database engine will process that index much more efficient in every "join" and "where" etc.

So, queries will perform faster, release locks earlier (if any) and use less system resources (memory and CPU). This will make the whole server perform better as there will be more resources available for other things.

Once learned the sql data types available and spending a few extra minutes when designing your schema will result in faster query execution and an overall better performing database.

The SQL Data Types reference sheet

The columns named 8, 9, 10 and 11 indicates SQL Server version data type support where

  • 8 = SQL Server 2000
  • 9 = SQL Server 2005
  • 10 = SQL Server 2008
  • 11 = SQL Server 2012
Datatype Min Max Storage 8 9 10 11 Type Notes
Bigint -2^63 2^63-1 8 bytes Exact
Int -2,147,483,648 2,147,483,647 4 bytes Exact
Smallint -32,768 32,767 2 bytes Exact
Tinyint 0 255 1 bytes Exact
Bit 0 1 1 to 8 bit columns in the same table requires a total of 1 byte, 9 to 16 bits = 2 bytes, etc... Exact
Decimal -10^38+1 10^38–1 Precision 1-9 = 5 bytes, precision 10-19 = 9 bytes, precision 20-28 = 13 bytes, precision 29-38 = 17 bytes Exact The Decimal and the Numeric data type is exactly the same. Precision is the total number of digits. Scale is the number of decimals. For both the minimum is 1 and the maximum is 38.
Numeric same as Decimal same as Decimal same as Decimal Exact
Money -2^63 / 10000 2^63-1 / 10000 8 bytes Exact
Smallmoney -214,748.3648 214,748.3647 4 bytes Exact
Float -1.79E + 308 1.79E + 308 4 bytes when precision is less than 25 and 8 bytes when precision is 25 through 53 Approx Precision is specified from 1 to 53.
Real -3.40E + 38 3.40E + 38 4 bytes Approx Precision is fixed to 7.
Datetime 1753-01-01 00:00:00.000 9999-12-31 23:59:59.997 8 bytes Datetime If you are running SQL Server 2008 or later and need milliseconds precision, use datetime2(3) instead to save 1 byte.
Smalldatetime 1900-01-01 00:00 2079-06-06 23:59 Datetime
Date 0001-01-01 9999-12-31 3 bytes no no Datetime
Time 00:00:00.0000000 23:59:59.9999999 no no Datetime Specifying the precision is possible. TIME(3) will have milliseconds precision. TIME(7) is the highest and the default precision. Casting values to a lower precision will round the value.
Datetime2 0001-01-01 00:00:00.0000000 9999-12-31 23:59:59.9999999 Presicion 1-2 = 6 bytes precision 3-4 = 7 bytes precision 5-7 = 8 bytes no no Datetime Combines the date datatype and the time datatype into one. The precision logic is the same as for the time datatype.
Datetimeoffset 0001-01-01 00:00:00.0000000 -14:00 9999-12-31 23:59:59.9999999 +14:00 Presicion 1-2 = 8 bytes precision 3-4 = 9 bytes precision 5-7 = 10 bytes no no Datetime Is a datetime2 datatype with the UTC offset appended.
Char 0 chars 8000 chars Defined width String Fixed width
Varchar 0 chars 8000 chars 2 bytes + number of chars String Variable width
Varchar(max) 0 chars 2^31 chars 2 bytes + number of chars no String Variable width
Text 0 chars 2,147,483,647 chars 4 bytes + number of chars String Variable width
Nchar 0 chars 4000 chars Defined width x 2 Unicode Fixed width
Nvarchar 0 chars 4000 chars Unicode Variable width
Nvarchar(max) 0 chars 2^30 chars no Unicode Variable width
Ntext 0 chars 1,073,741,823 chars Unicode Variable width
Binary 0 bytes 8000 bytes Binary Fixed width
Varbinary 0 bytes 8000 bytes Binary Variable width
Varbinary(max) 0 bytes 2^31 bytes no Binary Variable width
Image 0 bytes 2,147,483,647 bytes Binary Variable width. Prefer to use the varbinary(max) type as the image type will be removed in future versions.
Sql_variant Other Stores values of various SQL Server-supported data types, except text, ntext, and timestamp.
Timestamp Other Stores a database-wide unique number that gets updated every time a row gets updated.
Uniqueidentifier Other Stores a globally unique identifier (GUID).
Xml no Other Stores XML data. You can store xml instances in a column or a variable.
Cursor Other A reference to a cursor.
Table Other Stores a result set for later processing.

A note on precision

Space taken by value entries of the types specifying precision (Float, Decimal, DateTime2 etc) is always the same. It's the column definition that defines how much space each entry takes, not the size of the value itself. So a Decimal(25,5) value of 999.999 takes 13 bytes, not 5 bytes. Even a NULL value will take 13 bytes. The column is fixed-length. Even though this might seem bad there's a performance gain CPU-wise when working with fixed-length data (also remember that index trees contains these values and fixed-length storage requirements).

Another consideration is when summing a precision based value the resulting summed values datatype will be the same (if not casted) as the column definition and an arithmetic overflow might occur. If you know your values will, for instance, range from 0 to 999,99 there's no point from a space perspective to not define it as Decimal(9,2) anyways (the highest 5 byte definition). That way your sum result have more space available and you can perhaps avoid some casting. From a constraining perspective a Decimal(5,2) might be more appropriate, but maybe constraints requirements shouldn't be mixed up with data type decisions (well this is another discussion outside the scope of this article).

My best tip is to "Define your precision as the highest point before storage requirements increases".

Summary

Spend some time studying these sql data types. Correctly used sql data types will improve performance, save storage on disk and reduce backup times. It will also help in providing a consistent structure. Choosing sql data types is indeed an important part of constraining a database schema and communicating intended usage.

Version specific data types reference sheets

The SQL Server data types reference sheet have been extracted into version specific sheets. They are found at these locations: SQL Server 2012, SQL Server 2008, SQL Server 2005 and SQL Server 2000.

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