PostgreSQL - Subtract (-) Operator

The PostgreSQL - (subtract) operator is used to subtract two values. It operates on numerical values.

The example below describes how to use subtract operator in various conditions:

Consider a database table called Sample with the following records:

Using with WHERE Clause: To select records of table where difference of Var1 and Var2 column values is greater than 20, the query is given below.
```
SELECT * FROM Sample
WHERE Var1 - Var2 > 20;
```
The query will produce following result:

Data Var1 Var2

Data4 25 4

Data5 30 5

Data6 35 6
Using with AS Clause: The difference of Var1 and Var2 column values can be displayed in a different column using AS clause:
```
SELECT *, (Var1 - Var2) AS Diff FROM Sample;
```
The query will produce following result:

Data Var1 Var2 Diff

Data1 10 1 9

Data2 15 2 13

Data3 20 3 17

Data4 25 4 21

Data5 30 5 25

Data6 35 6 29
Using with UPDATE Clause: To update the column Var1 with the difference of columns Var1 and Var2, the query is given below:
```
UPDATE Sample
SET Var1 = Var1 - Var2;

--See result
SELECT * FROM Sample;
```
The query will produce following result:

Data Var1 Var2

Data1 9 1

Data2 13 2

Data3 17 3

Data4 21 4

Data5 25 5

Data6 29 6
Using with values: To subtract two values, we can simply use SELECT statement:
```
SELECT 50 - 30;
```
The query will produce following result:
```
20

(1 row) 
```