04 Try it yourself Interactive

The top line never moves

The schema is pinned at the top of the console and the instance sits underneath it. In Instance changes, nine steps run against it: an empty table to start, then seven writes — three inserts, one update, one delete and two the schema refuses — and a closing step that compares the design with where it started. Watch the pinned line the whole way and count how many times it moves. Then switch to Schema changes, where DDL leads and the pinned line is the thing that moves, but only after the rows already there agree to let it. Nothing plays on its own: Next, Back and Reset, or the arrow keys.

Instance changes · DML
schema v1 · 0 rows
Green = accepted, now part of the instance. Indigo = a cell this statement rewrote, or one the schema has only now given every row. Amber = look here, this is what you collided with. Rose = outside the state, whether it was refused on the way in or deleted on the way out.
Press Next to begin. Each press runs one statement.


      

        
Rows now0

        
Schema changes0

        
Accepted0

        
Refused0

      


      

      

        
        
        
        step 0 / 0