The order of the Input tables is essential.
The Main Row connection determines the Main flow table content. This input flow is reflected in the first table of the Map Editor's Input panel.
The Lookup connections' content fills in all other (secondary or subordinate) tables which displays below the Main flow table. If you have not define the schema of an input component yet, the input table displays as empty in the Input area.
The key is also retrieved from the schema defined in the Input component. This Key corresponds to the key defined in the input schema where relevant. It has to be distinguished from the hash key that is internally used in the Map Editor, which displays in a different color.