16.20 - Dropping Columns From a Table - Teradata Database - Teradata Vantage NewSQL Engine

Teradata Vantage™ SQL Data Definition Language Detailed Topics

Teradata Database
Teradata Vantage NewSQL Engine
Release Number
March 2019
Content Type
Programming Reference
Publication ID
English (United States)
Last Update
The following rules and restrictions apply to dropping columns from a table:
  • You cannot drop all of the columns from a table.
  • When you drop a column, Teradata Database deletes the field corresponding to the dropped column in every row in the table.
  • You cannot drop indexed columns from a table without first dropping the index on those columns.

    The following set of procedures explain what you must do to drop an indexed column from a table.

To drop a column on which this type of index is defined … Follow this procedure …
Primary: the table has no rows.
  1. Use the primary index or primary AMP index modification syntax of the ALTER TABLE statement to modify the table definition to create a new primary index or primary AMP index.
  2. Use ALTER TABLE table_name DROP column_name to drop the column set that was the former primary index or primary AMP index.
Primary: using the CREATE TABLE AS statement
  1. Copy the table into a newly defined table defined with a different primary index or primary AMP index using the CREATE TABLE AS syntax.
  2. Drop the original table.
  3. Rename the new table.
Primary: legacy method
  1. Create a new table with the correct primary index or primary AMP index.
  2. Copy the data into the new table.

    A simple way to do this is to use an INSERT … SELECT request. See “INSERT … SELECT” in Teradata Vantage™ SQL Data Manipulation Language , B035-1146 .

  3. Drop the original table.
  4. Rename the new table.
  • Secondary
  • Hash
  • Join
  1. Drop the index.
  2. Drop the index columns.
  3. Define a new index on the correct columns.
  • You cannot drop a partitioning column for a row-partitioned table without first modifying the partitioning to exclude that column from the partitioning set. Otherwise, Teradata Database returns an error.

    You cannot drop a column on which a primary, primary AMP index, secondary, hash, or join index is defined.

  • You cannot drop columns that are referenced in the UPDATE OF clause of a trigger.
  • You can drop the identity column from an existing table.
  • You can also drop only the identity column attribute from an identity column in an existing table, retaining the column and its data.
  • You can drop LOB columns from a base table without restrictions. If you drop all the LOB columns from a table, the table is not bound by the LOB restrictions. See Rules and Restrictions for Large Object Data Types.
  • You cannot drop the QITS column from a queue table.