Difference between numeric, float and decimal in SQL Server

Question

What are the differences between numeric, float and decimal datatypes and which should be used in which situations?

For any kind of financial transaction (e.g. for salary field), which one is preferred and why?

Answer 1

use the float or real data types only if the precision provided by decimal (up to 38 digits) is insufficient

• Approximate numeric data types do not store the exact values specified for many numbers; they store an extremely close approximation of the value.(Technet)

• Avoid using float or real columns in WHERE clause search conditions, especially the = and <> operators (Technet)

so generally because the precision provided by decimal is [10E38 ~ 38 digits] if your number can fit in it, and smaller storage space (and maybe speed) of Float is not important and dealing with abnormal behaviors and issues of approximate numeric types are not acceptable, use Decimal generally.

more useful information

• numeric = decimal (5 to 17 bytes) (Exact Numeric Data Type)
  • will map to Decimal in .NET
  • both have (18, 0) as default (precision,scale) parameters in SQL server
  • scale = maximum number of decimal digits that can be stored to the right of the decimal point.
  • kindly note that money(8 byte) and smallmoney(4 byte) are also exact and map to Decimal In .NET and have 4 decimal points(MSDN)
  • decimal and numeric (Transact-SQL) - MSDN
• real (4 byte) (Approximate Numeric Data Type)
  • will map to Single in .NET
  • The ISO synonym for real is float(24)
  • float and real (Transact-SQL) - MSDN
• float (8 byte) (Approximate Numeric Data Type)
  • will map to Double in .NET
• All exact numeric types always produce the same result, regardless of which kind of processor architecture is being used or the magnitude of the numbers
• The parameter supplied to the float data type defines the number of bits that are used to store the mantissa of the floating point number.
• Approximate Numeric Data Type usually uses less storage and have better speed (up to 20x) and you should also consider when they got converted in .NET
  • What is the difference between Decimal, Float and Double in C#
  • Decimal vs Double Speed
  • SQL Server - .NET Data Type Mappings (From MSDN)

main source : MCTS Self-Paced Training Kit (Exam 70-433): Microsoft? SQL Server? 2008 Database Development - Chapter 3 - Tables , Data Types , and Declarative Data Integrity Lesson 1 - Choosing Data Types (Guidelines) - Page 93