In Microsoft Dynamics CRM, every field has a datatype property, which specifies the type of information that will be stored in the field. The datatype cannot be changed, so it is an important consideration to make when customizing your system.
The datatypes available in Microsoft Dynamics CRM 2011 and the corresponding SQL Server datatypes are shown in the following table:

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CRM datatype                  SQL Server datatype

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Single line of text                   Nvarchar
Option set                                      Int
Two options                                   Bit
Whole number                              Int
Floating point number             Float
Decimal number                    Decimal
Currency                                  Money

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CRM datatype                SQL Server datatype

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Multiple lines of text         nvarchar(max)
Date and time                       Datetime
Lookup                                 Uniqueidentifier