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Delta Lake
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Delta column mapping

Column mapping feature allows Delta table columns and the underlying Parquet file columns to use different names. This enables Delta schema evolution operations such as RENAME COLUMN and DROP COLUMNS on a Delta table without the need to rewrite the underlying Parquet files. It also allows users to name Delta table columns by using characters that are not allowed by Parquet, such as spaces, so that users can directly ingest CSV or JSON data into Delta without the need to rename columns due to previous character constraints.

How to enable Delta Lake column mapping

Section titled “How to enable Delta Lake column mapping”

Column mapping requires the following Delta protocols:

  • Reader version 2 or above.
  • Writer version 5 or above.

For a Delta table with the required protocol versions, you can enable column mapping by setting delta.columnMapping.mode to name.

You can use the following command to upgrade the table version and enable column mapping:

ALTER TABLE <table_name> SET TBLPROPERTIES (
  'delta.minReaderVersion' = '2',
  'delta.minWriterVersion' = '5',
  'delta.columnMapping.mode' = 'name'
)

Rename a column

Section titled “Rename a column”

When column mapping is enabled for a Delta table, you can rename a column:

ALTER TABLE <table_name> RENAME COLUMN old_col_name TO new_col_name

For more examples, see Rename columns.

Drop columns

Section titled “Drop columns”

When column mapping is enabled for a Delta table, you can drop one or more columns:

ALTER TABLE table_name DROP COLUMN col_name;


ALTER TABLE table_name DROP COLUMNS (col_name_1, col_name_2, ...);

For more details, see Drop columns.

Supported characters in column names

Section titled “Supported characters in column names”

When column mapping is enabled for a Delta table, you can include spaces as well as any of these characters in the table’s column names: ,;{}()\n\t=.

Known limitations

Section titled “Known limitations”