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Precision and Rounding of FLOAT Values in SQL Server Transact-SQL
How REAL and FLOAT Literal Values Are Rounded in SQL Server Transact-SQL?
✍: FYIcenter.com
By definition, FLOAT(n) should store the mantissa of the floating number in n bits. For example, FLOAT(16) should have a precision one-byte less than FLOAT(24).
However, SQL Server Transact-SQL only supports two precisions for floating numbers:
The tutorial exercise below shows you some different precision and rounding examples:
-- FLOAT(1) works like FLOAT(24) DECLARE @x FLOAT(1) SET @x = 9.234567890E+10; SELECT @x; ------------ 9.234568E+10 -- 7 digits precision -- Single precision with rounding DECLARE @x REAL; -- FLOAT(24) SET @x = 9.234567890E+10; SELECT @x; ------------ 9.234568E+10 -- 7 digits precision -- FLOAT(25) works like FLOAT(53) DECLARE @x FLOAT(25); SET @x = 9.2345678901234567890E+100; SELECT @x; --------------------- 9.23456789012346E+100 -- 15 digits precision -- Double precision with rounding DECLARE @x FLOAT(53); SET @x = 9.2345678901234567890E+100; SELECT @x; --------------------- 9.23456789012346E+100 -- 15 digits precision
In other words, Transact-SQL is not truly respecting FLOAT(n) declaration.
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2017-04-19, 5940👍, 0💬
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