Map columns decides which source column fills each target column of a Writeback table. Use the Columns step after you set the source on General, and before the table runs.
A target column is a column of the destination table you imported, so import the table first if you have not: see Import destination tables. While the table is not deployed, the editor shows the banner Please finish column mapping to enable this table, with a Columns button that opens this step.
Map a source column to a target column
Open the Writeback table and select Columns.
Find the target column's row in the Column Mapping table. There is one row per target column, and rows follow the destination table's own column order.
Under Source Columns, choose the column that fills it. The box is empty until you choose, and reads Select source column. Choosing No mapping clears the row.
You can also drag a column chip from Unmapped Source Columns onto the row.
Watch the counter above the table. It appears once at least one column is mapped and counts the columns that have a source, for example 2 of 5 mapped.
Click Apply to save the mapping. The table is deployed, it counts as Mapped in the tree, and the editor moves to Dependencies.
The step has three areas:
Area
What it holds
Column Mapping
One row per target column, with its Data Type and the source column chosen for it.
Skip Target Columns
Target columns that take no source. While it is empty it reads No skipped columns.
Unmapped Source Columns
Source columns that no target column uses yet. When none are left it reads All columns mapped.
To leave a target column unfilled, click the x on its row, or drag the column chip onto Skip Target Columns. The tooltip on the x reads Remove from list. Skipping a column also clears its source choice.
To bring it back, click the chip or its plus button in Skip Target Columns (the tooltip reads Add column back to list), or drag the chip back into the table. The restored row is highlighted and scrolled into view.
A skipped column receives an empty value (NULL) on every run. Map the column if you want it filled.
Clear mappings
A row you mapped shows a Clear mapping button. It clears that row's source choice.
Clear All removes the source choices of every row that is not skipped. The Data Type of each row and the skipped columns stay as they are. The button is greyed out while nothing is mapped.
What saving the mapping does
Apply stores the mapping exactly as you see it, replacing the saved one, and confirms with Column mappings saved successfully.
Each column ends up in one of two stored states: mapped or skipped. A target column you left with no source is stored as skipped when you save, and it receives an empty value on every run until you map it.
Saving the mapping deploys the table, so it counts as Mapped and its workflow can run it.
A source column counts as mapped when any row uses it. For a table that writes a query, a mapping is stored by the source column's name.
If a later change on General leaves the table with no chosen column, the table is no longer deployed and does not run until a mapping is saved again. See Configure a Writeback table.
The tree shows the table as Unmapped until you save a mapping. If it still shows an older state, refresh it.
Limits and edge cases
One source column fills one target column at a time. Choosing it in a second row removes it from the first.
Dragging a column onto the row it already fills is refused. To drop a mapping, drag its chip back into Unmapped Source Columns, or use Clear mapping.
Rows disabled by a foreign key or an audit row show a Lock icon, with the tooltip Disabled due to foreign key constraint or Disabled because it's an audit row.
A new table needs at least one column chosen or skipped before the step can be saved.
A Data Type in red blocks Apply while its column is not skipped. See Data types for columns.
A table that writes a query shows Please validate your query in the General tab first until its query is validated. Open General, click Validate, then return to Columns.
If no source is chosen for the table, the step reads No table selected for column mapping. Set the source on General first.
If the mapping cannot load, the step shows Failed to load column mapping data. with a Retry button.
When there are no target columns to save, saving stops with No target columns available to save mappings.
An empty value (NULL) on every run. Map the column to a source column if you want it filled.
Why did a target column move to Skip Target Columns?
It has no source column chosen. When you save, a target column left with no source is stored as skipped, and it receives an empty value on every run until you map it. Bring the column back and choose a source if that is not what you want.
I skipped a column by mistake. How do I bring it back?
Click the chip or its plus button in Skip Target Columns (the tooltip reads Add column back to list), or drag the chip back into the table. The row is highlighted and scrolled into view. Save the step to keep the change.
Can I send one source column to two target columns?
No. Each source column fills one target column at a time. Choosing it in a second row removes it from the first.
Does changing a Data Type change my destination table?
No. It sets the type each value is converted to before it is written; the column in the destination keeps its own type. See Data types for columns.
Does a wrong Data Type on a skipped column block Apply?
No. Only columns that are not skipped are checked, so a red Data Type on a skipped column does not block the save.
Why does the editor say "Please fix column mapping errors before continuing"?
At least one row has a Data Type that is empty or not recognised, marked in red. Fix those rows. For a new table, the step also needs at least one column chosen or skipped.
Why does the Columns step say "Please validate your query in the General tab first"?
The table takes its rows from a query, and the query is not validated yet, so the mapping cannot show. Open General, click Validate, then return to Columns. See Configure a Writeback table.
What does Clear All clear?
It removes the source choices of every row that is not skipped. The Data Type of each row and the skipped columns stay as they are. The button is greyed out while nothing is mapped.