The Preview tab of a table's popup shows the table's data without running a load. It has two sides: Lake shows the rows stored in the Lake table, and Source reads the data from the table's datasource, so you can check a table before you deploy it or after a load.
Preview is one of the popup's four main tabs, next to Table, Dependant and Settings; the rest of the popup is described on Configure a table.
| Side | What it shows | When it is available |
|---|---|---|
| Lake | The rows stored in the Lake table. | Only after the table is deployed |
| Source | The data read from the table's datasource. | Before and after the table is deployed |
On a table that is not deployed, the tab shows Source and greys out Lake, with the tooltip Deploy the table to preview lake data on the greyed side; deploy the table to unlock it (see Deploy a table). Screen readers name the two sides Lake preview and Source preview. The popup remembers the side you last chose for a table, so the preview opens the same way next time, even after a page reload.
If the preview cannot load the lake data and the grid is still empty, the tab shows a Preview Error panel with the reason when there is one, Failed to load preview data when there is none, and a Retry button. Click Retry to read the data again.
Rows that are already on screen stay visible: the panel appears only when there is nothing to show yet, so a failed reload does not replace rows that are already on screen.
Use the Export data control in the preview toolbar. The file is named after the table; in Source mode the name gets a _Source suffix, so the two sides stay apart: a table orders exports as orders from Lake and as orders_Source from Source.
The control, its formats and the rest of the toolbar are described on Table preview, filters and export.
Lake shows the rows stored in the Lake table, and Source reads the data from the table's datasource. Source is the side that works before the table is deployed.
The table is not deployed yet, so there is no lake data to preview. Deploy it first (see Deploy a table); until then, the tooltip reads Deploy the table to preview lake data.
The side you chose last for that table: the popup remembers it, even after a page reload. A table that is not deployed shows Source and greys out Lake.
The preview could not load the lake data. The panel shows the reason when one is available, and Failed to load preview data when there is none. Click Retry to read the data again; if it keeps failing, see Lake troubleshooting.
They stay visible. The Preview Error panel appears only when there is no data to show yet, so a failed reload does not replace rows that are already on screen.
No. A preview reads the data and shows it; it does not load rows or change the table. To load a table, synchronize it from the Settings tab (see Run, stop and troubleshoot loads).
It reads the preview again for the side you are on: the lake rows in Lake, and the datasource rows in Source.