I've been reading <http://godoc.org/github.com/gocql/gocql>
Yet I don't understand how to do INSERT -- IF NOT EXIST with gocql.   

It stated that   

> 
> func (\*Query) ScanCAS
> 
> 
> func (q \*Query) ScanCAS(dest ...interface{}) (applied bool, err error)
> 
> 
> ScanCAS executes a lightweight transaction (i.e. an UPDATE or INSERT statement containing an IF clause). If the transaction fails because the existing values did not match, the previous values will be stored in dest.
> 
> 
> 

When I run

```
cluster := gocql.NewCluster("127.0.0.1")
cluster.Keyspace = "example"
cluster.Consistency = gocql.Quorum
session, _ := cluster.CreateSession()
defer session.Close()

var mapQ map[string]interface{}
var inserted bool
var id gocql.UUID
var timeline, text string
// insert a tweet
isTrue, err := session.Query(`INSERT INTO tweet (timeline, id, text) VALUES (?, ?, ?) IF NOT EXIST`,
    "hermano", gocql.TimeUUID(), "good night").
    ScanCAS(); if err != nil {
    log.Println(err)
}
fmt.Println(timeline, id, text)
fmt.Printf("%+v\n", isTrue)
fmt.Printf("%+v\n", inserted)
fmt.Printf("%+v\n", mapQ)

```

I get:   

`Failed parsing statement: [INSERT INTO tweet (timeline, id, text) VALUES (?, ?, ?) IF NOT EXIST] reason: ArrayIndexOutOfBoundsException -1`

So my question is:   

 1. How to actually do INSERT IF NOT EXIST in gocql? Can you guys give me any example?  

 2. How to do proper ScanCAS?  

 3. What makes MapScanCAS and ScanCAS different? I don't understand [what column mismatching are the author is talking about](http://godoc.org/github.com/gocql/gocql#Query.MapScanCAS)  

 4. Are there any good page that explains gocql beside its godoc page?