Question: I'm trying to toggle between an active and inactive button based on whether or not the Session variable is `true` or `false`.

On a child component, I declare the Session variable:

```
  choice(e){
    e.preventDefault();
  ...
    Session.set("upNext", true);
   ...

  };

```

Then, on the parent component, I place this code in the render(){} function:

```
render(){

let upNext;
if(Session.get("upNext")){
upNext = <button className="ui right huge labeled icon primary button" onClick={this.nextPosition.bind(this)}><i className="right arrow icon"></i>Next</button>
} else{
upNext = <button className="ui right huge labeled icon primary button disabled" onClick={this.nextPosition.bind(this)}><i className="right arrow icon"></i>Next</button>
}

  return(
    <div className="ui container">
      {upNext}
    </div>
  }

```

Finally, in the `componentWillMount()` method, I set the Session variable to `false` to reset before the next component loads.

The Session variable triggers, changes from false to true, but the code inside the first conditional (if Session.get is equal to true) never gets run. Never had this problem happen when working with Blaze, so there must be something here that I'm completely missing.

Answer: 
Hmmm . . . How about `select`:

```
Select A.*
from A left outer join
     B
     on A.ID = B.ID
where B.ID IS NULL;

```

I removed the `B` columns because they are not needed.
One of your join columns may have `NULL` values. Whenever there is `NULL` in any of the join key values, it will skip that column. Try replacing the `NULL` with some default value while joining using `NVL` or `COALESCE`. I was looking for same answer and saw your post here. But there was no solution. But since i found the solution I just wanted to post here so that someone can benefit.

```sql
select *
from A
left outer join B
on coalesce(A.ID,000) = coalesce(B.ID,000)
where B.ID IS NULL

```