# DECIMAL datatype behavior while doing calculations in Teradata

Scenario: Look at the following result we get in Teradata. when multiplying two decimal the result data has double decimal precision

```
SELECT TYPE(CAST (2.3 AS DECIMAL(18,4)) * CAST (2.3 AS DECIMAL(18,4)) )
```

The result is:

```
DECIMAL(18,8)
```

- Teradata's basic rules are:
When you add / substract / divide DECIMALs the resulting fractional precision is the greater of both operands, e.g. dec(10,2) + dec(10,4) = dec(xx,4)
- But when you multiply the fractional digits are added, e.g.dec(10,2) * dec(10,4) = dec(xx,6)
- And then there's the most important rule, people tend to forget: After each calculation the result is rounded to this precision

**Example:**

```
sel 2.0/3.00 * 100, 100*2.0/3.00;
*** Query completed. One row found. 2 columns returned.
*** Total elapsed time was 1 second.
((2.0/3.00)*100) ((100*2.0)/3.00)
----------------- -----------------
67.00 66.67
```

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