Difference between DECIMAL and NUMERIC datatype in PSQL

问题

what is the use of decimal and numeric datatype in postgreSQL. As per the reference the following is the explanation given to these datatypes.

Decimal,numeric --> It is a user specified precision, exact and range up to 131072 digits before the decimal point and up to 16383 digits after the decimal point.

The above statement shows the description of decimal and numeric datatype. But, still I didn't understand what is the exact use of these data type and where it is used instead of other datatypes.

Answer with example is much appreciated...

回答1:

Right from the manual:

The types decimal and numeric are equivalent. Both types are part of the SQL standard.

As for the "why do I need to use it", this is also explained in the manual:

The type numeric can store numbers with a very large number of digits and perform calculations exactly

(Emphasis mine).

If you need numbers with decimals, use decimal (or numeric) if you need numbers without decimals, use integer or bigint. A typical use of decimal as a column type would be a "product price" column or an "interest rate". A typical use of an integer type would be e.g. a column that stores how many products were ordered (assuming you can't order "half" a product).

double and real are also types that can store decimal values, but they are approximate types. This means you don't necessarily retrieve the value you stored. For details please see: http://floating-point-gui.de/

回答2:

Quoted straight from https://www.postgresql.org/message-id/20211.1325269672@sss.pgh.pa.us

There isn't any difference, in Postgres. There are two type names because the SQL standard requires us to accept both names. In a quick look in the standard it appears that the only difference is this:

     17)NUMERIC specifies the data type exact numeric, with the decimal
        precision and scale specified by the <precision> and <scale>.

     18)DECIMAL specifies the data type exact numeric, with the decimal
        scale specified by the <scale> and the implementation-defined
        decimal precision equal to or greater than the value of the
        specified <precision>.

ie, for DECIMAL the implementation is allowed to allow more digits than requested to the left of the decimal point. Postgres doesn't exercise that freedom so there's no difference between these types for us.

      regards, tom lane

回答3:

They are the synonym of each other and functionally same. The SQL:2003 standard says:

21) NUMERIC specifies the data type
    exact numeric, with the decimal
    precision and scale specified by the
    <precision> and <scale>.

22) DECIMAL specifies the data type
    exact numeric, with the decimal scale
    specified by the <scale> and the
    implementation-defined decimal
    precision equal to or greater than the
    value of the specified <precision>.

来源：https://stackoverflow.com/questions/33730538/difference-between-decimal-and-numeric-datatype-in-psql