ALTER TABLE

Modifies the columns and properties of a table.

Add new columns, drop existing columns, renames columns, and change table properties. The command returns no results.

Restriction:
  • Can only rename clustering columns in the primary key.
  • Cannot change the data type of a column.
  • For a table that has a materialized view, cannot drop a column from the table even if the column is not used in the materialized view.
  • Cannot rename or drop columns that have dependent secondary indexes or Datastax Enterprise Search indexes.
  • Do not add a column with the same name as an existing column but with a different data type. It will prevent commit log replays and corrupt existing SSTables with old data.
Note: ALTER COLUMNFAMILY is deprecated.

Synopsis

ALTER TABLE [keyspace_name.]table_name 
  [ ADD ( column_definition | column_definition_list ) ]
  [ DROP ( column | column_list | COMPACT STORAGE ) ]
  [ RENAME column_name TO column_name ]
  [ WITH table_properties [ , ... ] ] ;
Table 1. Legend
Syntax conventions Description
UPPERCASE Literal keyword.
Lowercase Not literal.
Italics Variable value. Replace with a user-defined value.
[] Optional. Square brackets ( [] ) surround optional command arguments. Do not type the square brackets.
( ) Group. Parentheses ( ( ) ) identify a group to choose from. Do not type the parentheses.
| Or. A vertical bar ( | ) separates alternative elements. Type any one of the elements. Do not type the vertical bar.
... Repeatable. An ellipsis ( ... ) indicates that you can repeat the syntax element as often as required.
'Literal string' Single quotation ( ' ) marks must surround literal strings in CQL statements. Use single quotation marks to preserve upper case.
{ key : value } Map collection. Braces ( { } ) enclose map collections or key value pairs. A colon separates the key and the value.
<datatype1,datatype2> Set, list, map, or tuple. Angle brackets ( < > ) enclose data types in a set, list, map, or tuple. Separate the data types with a comma.
cql_statement; End CQL statement. A semicolon ( ; ) terminates all CQL statements.
[--] Separate the command line options from the command arguments with two hyphens ( -- ). This syntax is useful when arguments might be mistaken for command line options.
' <schema> ... </schema> ' Search CQL only: Single quotation marks ( ' ) surround an entire XML schema declaration.
@xml_entity='xml_entity_type' Search CQL only: Identify the entity and literal value to overwrite the XML element in the schema and solrConfig files.
ADD column_defintion | ( column_definition_list )
Add one or more columns and set the data type. Set the column name followed by the data type. The value is automatically set to null. To add multiple columns, use a comma separated list of columns placed inside parentheses.
column_name cql_type [ , ]
[ column_name cql_type [ , ... ]
Restriction: Adding columns to a primary key is not supported after a table has been created.
DROP column | ( column_list )

Drop one or more columns. The values contained in the row are also dropped and not recoverable. To drop multiple columns, use a comma separated list of columns placed inside parentheses.

RENAME column_name TO column_name
Changes the name of a primary key column and preserves the existing values.
Restriction: Not supported on materialized view base-tables, or tables with secondary indexes or Datastax Enterprise Search indexes.
table_properties
You can modify an existing table's properties. Some properties are single options that are set to a value:
option_name = value [ AND ... ]
For example, speculative_retry = '10ms'. Enclose the value for a string property in single quotation marks.

Other table properties are set using a JSON map: option_name = { subproperty_name : value [ , ... ] }

See table_options for more details.

Examples

Specifying the table and keyspace

You can qualify the table name by prepending the name of its keyspace. For example, to specify the teams table in the cycling keyspace:

ALTER TABLE cycling.teams
ADD manager uuid;

Adding a column

To add a column to a table, use the ADD instruction; for example:

ALTER TABLE cycling.cyclist_races 
ADD firstname text;

To add a column of a collection type:

ALTER TABLE cycling.upcoming_calendar 
ADD events list<text>;

This operation does not validate the existing data.

You cannot use the ADD instruction to add:

  • A column with the same name as an existing column.
  • A static column if the table has no clustering columns and uses COMPACT STORAGE.

Dropping a column

To remove a column from the table, use the DROP instruction:
ALTER TABLE cycling.basic_info 
DROP birth_year;

DROP removes the column from the table definition. The column becomes unavailable for queries immediately after it is dropped. The database drops the column data during the next compaction.

Restriction:
  • If you drop a column then re-add it, DataStax Distribution of Apache Cassandra™ does not restore the values written before the column was dropped.
  • Do not re-add a dropped column that contained timestamps generated by a client; you can re-add columns with timestamps generated by the write time facility.
  • You cannot drop columns from tables defined with the COMPACT STORAGE option.

Renaming a column

The main purpose of RENAME is to change the names of CQL-generated primary key and column names that are missing from a legacy table. The following restrictions apply to the RENAME operation:
  • You can only rename clustering columns, which are part of the primary key.
  • You cannot rename the partition key because the partition key determines the data storage location on a node. If a different partition name is required, the table must be recreated and the data migrated.
    Note: There are many restrictions when using RENAME because SSTables are immutable. To change the state of things on disk, everything must be rewritten.
  • You can index a renamed column.
  • You cannot rename a column if an index has been created on it.
  • You cannot rename a static column.

Modifying table properties

To change an existing table's properties, use ALTER TABLE and WITH. You can specify a:

This example uses the WITH instruction to modify the read_repair_chance property, which configures read repair for tables that use for a non-quorum consistency and how to change multiple properties using AND:

ALTER TABLE cyclist_mv
WITH comment = 'ID, name, birthdate and country'
AND read_repair_chance = 0.2;

Enclose a text property value in single quotation marks. You cannot modify properties of a table that uses COMPACT STORAGE.

Modifying compression and compaction

Use a property map to alter a table's compression or compaction setting:

ALTER TABLE cycling_comments 
WITH compression = { 
  'sstable_compression' : 'DeflateCompressor', 
  'chunk_length_kb' : 64
};

Enclose the name of each key in single quotes. If the value is a string, enclose this in quotes as well.

CAUTION: If you change the compaction strategy of a table with existing data, the database rewrites all existing SSTables using the new strategy. This can take hours, which can be a major problem for a production system. For strategies to minimize this disruption, see How to change the compaction strategy on a production cluster and Impact of Changing Compaction Strategy.

Changing caching

Set the number of rows per partition to store in the row cache for a table to 10 rows:

ALTER TABLE cycling.events 
WITH caching = {
  'keys': 'NONE', 
  'rows_per_partition': 10
};

Reviewing the table definition

Use DESCRIBE or DESC to view the table definition.
DESC TABLE cycling.events;

The table details including the column names are returned.

CREATE TABLE cycling.events (
  month int,
  end timestamp,
  class text,
  title text,
  location text,
  start timestamp,
  type text,
  PRIMARY KEY (month, end, class, title)
)
WITH CLUSTERING ORDER BY (end ASC, class ASC, title ASC)
AND bloom_filter_fp_chance = 0.01
AND caching = {'keys': 'NONE', 'rows_per_partition': '10'}
AND comment = ''
AND compaction = {'class': 'org.apache.cassandra.db.compaction.SizeTieredCompactionStrategy',
  'max_threshold': '32', 'min_threshold': '4'}
AND compression = {'chunk_length_in_kb': '64',
  'class': 'org.apache.cassandra.io.compress.LZ4Compressor'}
AND crc_check_chance = 1.0
AND dclocal_read_repair_chance = 0.1
AND default_time_to_live = 0
AND gc_grace_seconds = 864000
AND max_index_interval = 2048
AND memtable_flush_period_in_ms = 0
AND min_index_interval = 128
AND read_repair_chance = 0.0
AND speculative_retry = '99PERCENTILE';