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Cast or Convert

SQL Server programmers can choose between two functions in SQL Server for converting expressions from one type to another. In many cases there will be a need within a stored procedure or other routine to convert data from, say, a datetime type to a varchar type; CONVERT and CAST are used for such things.

Because SQL Server provides both functions, there may be some confusion about which is best to use and under what circumstances. CONVERT is specific to SQL Server, and allows for a greater breadth of flexibility when converting between date and time values, fractional numbers, and monetary signifiers.

CAST is the more ANSI-standard of the two functions, meaning that while it's more portable (i.e., a function that uses CAST can be used in other database applications more or less as-is), it's also less powerful. CAST is also required when converting between decimal and numeric values to preserve the number of decimal places in the original expression. For those reasons, it's best to use CAST first, unless there is some specific thing that only CONVERT can provide

Syntax:
CAST ( xx as decimal)
CONVERT(decimal, xx )

Query: select cast(-0.00000000000000000000000000000000000000118 as real) as [cast result]
Output:
The number '0.00000000000000000000000000000000000000118' is out of the range for numeric representation (maximum precision 38).

Query: select convert(real, '-0.00000000000000000000000000000000000000118') as [convert result]
Output: 0
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