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Union Tables

Data > Union tables... stacks two or more open tabs on top of each other into one new table, like appending several exports of the same shape.

How it works

Tick the tabs to combine. Octa builds a reconciliation plan: the result has the union of all their columns. For each merged column you can keep or drop it and choose its target type. Columns that appear in only some tables are filled with empty cells for the rest. Mixed numeric types widen to a common number type; otherwise the column falls back to text.

Apply opens the combined result in a new tab, leaving the sources untouched.

Union files straight from the sidebar

You do not have to open a tab per file first. In the directory sidebar:

  1. Ctrl-click each file you want (Shift-click selects a whole run between the last click and this one). Selected rows stay highlighted, and a N selected bar appears at the top of the sidebar.
  2. Click Union... in that bar, or right-click any selected file and choose Union selected files....

Octa reads the files and opens the same reconciliation plan as above, with one checkbox per file instead of per tab. This is the quick way to stack a folder of partitioned exports: forty part-*.parquet files become one table without forty tabs. It is not parquet-specific, and the files need not even share a format: any mix Octa can read (CSV, JSON, parquet, ...) unions together, since the columns are reconciled either way.

A plain click still opens a file as before, and clears the selection. Files that cannot be read are skipped, and the status bar reports how many.

Union files in the cloud

The same works in the cloud sidebar. Ctrl-click the objects you want, then click Union... in the selection bar that appears at the top of the cloud section.

Octa downloads the selected objects in the background and then opens the same reconciliation dialog. A folder of partitioned parquet parts in S3, Azure Blob or GCS becomes one table without opening a tab per object. As with local files, a plain click still just opens the object.

Command line and assistant

Also available as octa --union (see the --union reference) and as the union_tables MCP / assistant tool. To match rows side-by-side on a key instead of stacking them, use Join Tables.