How do I interpret precision and scale of a number in a database?

I have the following column specified in a database: decimal(5,2)

How does one interpret this?

According to the properties on the column as viewed in SQL Server Management studio I can see that it means: decimal(Numeric precision, Numeric scale).

What do precision and scale mean in real terms?

It would be easy to interpret this as a decimal with 5 digits and two decimals places...ie 12345.12

P.S. I've been able to determine the correct answer from a colleague but had great difficulty finding an answer online. As such, I'd like to have the question and answer documented here on stackoverflow for future reference.

Numeric precision refers to the maximum number of digits that are present in the number.

ie 1234567.89 has a precision of 9

Numeric scale refers to the maximum number of decimal places

ie 123456.789 has a scale of 3

Thus the maximum allowed value for decimal(5,2) is 999.99

Precision of a number is the number of digits.

Scale of a number is the number of digits after the decimal point.

What is generally implied when setting precision and scale on field definition is that they represent maximum values.

Example, a decimal field defined with precision=5 and scale=2 would allow the following values:

• 123.45 (p=5,s=2)
• 12.34 (p=4,s=2)
• 12345 (p=5,s=0)
• 123.4 (p=4,s=1)
• 0 (p=0,s=0)

The following values are not allowed or would cause a data loss:

• 12.345 (p=5,s=3) => could be truncated into 12.35 (p=4,s=2)
• 1234.56 (p=6,s=2) => could be truncated into 1234.6 (p=5,s=1)
• 123.456 (p=6,s=3) => could be truncated into 123.46 (p=5,s=2)
• 123450 (p=6,s=0) => out of range

Note that the range is generally defined by the precision: |value| < 10^p ...

Precision, Scale, and Length in the SQL Server 2000 documentation reads:

>Precision is the number of digits in a number. Scale is the number of digits to the right of the decimal point in a number. For example, the number 123.45 has a precision of 5 and a scale of 2.

Precision refers to the total number of digits while scale refers to the digits allowed after the decimal. The example quoted by would have a precision of 7 and a scale of 2.

Moreover, DECIMAL(precision, scale) is an exact value data type unlike something like a FLOAT(precision, scale) which stores approximate numeric data. For example, a column defined as FLOAT(7,4) is displayed as -999.9999. MySQL performs rounding when storing values, so if you insert 999.00009 into a FLOAT(7,4) column, the approximate result is 999.0001.

Let me know if this helps!