TABLE:

```
 item    value
  a        1
  a        1
  a        1
  b        2
  b        2
  c        1
  c        1 

```

I want the result like this

```
 SUM
  4

```

It can be done by the following command :

```
SELECT SUM(value)
FROM (
    SELECT DISTINCT ON (item) *
    FROM TABLE
) s 

```

But is there a simple command to do this?
Something like this:

```
SELECT SUM(value in DISTINCT(item)) FROM TABLE

```