Moves an existing column to a new position in the table schema without rewriting data files.
ALTER TABLE <table> CHANGE COLUMN <column> FIRST | AFTER <other_column>## Overview Repositions an existing column within the table schema. This is a metadata-only operation that updates the column ordering in the Delta log without rewriting or touching any data files. ## Behavior - The column must exist in the current schema. If the column is not found, the command fails. - When FIRST is specified, the column is moved to position 0 in the schema field list. - When AFTER <other_col> is specified, the column is moved to the position immediately following the referenced column. - If the referenced AFTER column does not exist, the command fails. - The operation emits a single metadata-only commit to the Delta log. - Two syntax variants are supported: `CHANGE COLUMN <col> FIRST|AFTER` and `ALTER COLUMN <col> FIRST|AFTER`. Both produce the same result. - After the column is moved, the schema observer is notified so the catalog stays in sync. ## Compatibility This is a DeltaForge extension. Column ordering is stored in the Delta schema metadata, which all Delta readers respect. The physical column order in Parquet files is unchanged; readers map columns by name (when column mapping is enabled) or by ordinal position.
| Name | Type | Description |
|---|---|---|
table | Fully qualified table name or registered table name. The table must be registered in the current session. | |
column_name | Column to move. | |
position | FIRST or column name to place after. |
-- Move a column to the first position
ALTER TABLE warehouse.clinical.patients CHANGE COLUMN mrn FIRST;-- Move a column after another column
ALTER TABLE warehouse.clinical.patients CHANGE COLUMN first_name AFTER mrn;-- Alternative syntax using ALTER COLUMN
ALTER TABLE warehouse.sales.orders ALTER COLUMN order_date AFTER order_id;-- Move a column to the beginning using ALTER COLUMN
ALTER TABLE warehouse.sales.orders ALTER COLUMN order_ref FIRST;