ALTER TABLE
Update a table’s definition or schema.
SyntaxALTER TABLE <table_name>
{ ADD PRIMARY KEY ( <column_name> [ , ... ] )
| DROP PRIMARY KEY
| ADD COLUMNS ( <column_name> <data_type> [ , ... ] )
| DROP COLUMN <column_name>
| { ALTER | MODIFY | CHANGE } COLUMN <old_name> <new_name> <data_type>
| MODIFY COLUMN <column_name>
SET MASKING POLICY <function_name> ( <column_name> [, ... ] )
| UNSET MASKING POLICY <function_name>
| { ADD | DROP } ROW ACCESS POLICY <function_name> ( <column_name> [, ... ] )
| LOCALSORT BY ( <column_name> [ , ... ] )
| REFRESH METADATA
[ FOR PARTITIONS ( <partition_name> = '<value>') ]
[ { AVOID | AUTO } PROMOTION ]
[ { FORCE | LAZY } UPDATE ]
[ { MAINTAIN | DELETE } WHEN MISSING ]
| FORGET METADATA
| SET TBLPROPERTIES ( '<property_name>' = '<property_value>' [ , ... ] )
| UNSET TBLPROPERTIES ( '<property_name>' [ , ... ] )
| CREATE AGGREGATE REFLECTION <reflection_name> USING
{ DIMENSIONS ( <column_name> [ , ... ] )
| MEASURES ( <column_name> ( <aggregation_type> ) [ , ... ] )
| DIMENSIONS ( <column_name> [ , ... ] ) MEASURES ( <column_name> ( <aggregation_type> ) [ , ... ] ) }
[ PARTITION BY ( { <column_name> | <partition_transform> } [ , ... ] ) ]
[ LOCALSORT BY ( <column_name> [ , ... ] ) ]
| CREATE EXTERNAL REFLECTION <reflection_name> USING <table_name>
| CREATE RAW REFLECTION <reflection_name> USING DISPLAY ( <column_name> [ , ... ] )
[ PARTITION BY ( { <column_name> | <partition_transform> } [ , ... ] ) ]
[ LOCALSORT BY ( <column_name> [ , ... ] ) ]
| DROP REFLECTION <reflection_name>
| REFRESH REFLECTIONS
| ROUTE REFLECTIONS TO { DEFAULT QUEUE | QUEUE { <queue_name> | <queue_uuid> } }
| { ADD | DROP } PARTITION FIELD { <column_name> | <partition_transform> }
}
Parameters
<table_name> String
The name of the table that you want to alter.
ADD PRIMARY KEY ( <column_name> [, ... ] ) String
Specifies to use one or more existing columns as the primary key of a table. Primary keys provide hints to the query planning during join planning. They can be added to Apache Iceberg tables only. Uniqueness of the values in a primary key is not enforced.
DROP PRIMARY KEY String
Removes an Iceberg table's primary key. The columns that make up the primary key remain in the table.
ADD COLUMNS ( <column_name> <data_type> [ , ... ] ) String
Creates one or more columns that have the specified names, data types, and character limits. The size is an attribute of the data type.
These are the supported primitive types:
- BOOLEAN
- VARBINARY
- DATE
- FLOAT
- DECIMAL
- DOUBLE
- INTERVAL
- INT
- BIGINT
- TIME
- TIMESTAMP
- VARCHAR (The length is always 65536 bytes. If a length is specified, it is ignored.)
You can define complex types by using either of these two sets of syntax:
Set 1
- struct_type:
ROW( name primitive_or_complex_type, .. ) - list_type:
ARRAY(primitive_or_complex_type)
Examples:
ROW(innerfield INT, anotherinnerfield DOUBLE)
ARRAY(INT)
ROW(innerfield ARRAY(INT))
ARRAY(ROW(innerfield INT))
Set 2
- struct_type:
STRUCT <name : primitive_or_complex_type, ... > - list_type:
{ LIST | ARRAY } < primitive_or_complex_type >
Examples:
STRUCT<innerfield : INT, anotherinnerfield : DOUBLE>
LIST<INT>
ARRAY<INT>
STRUCT<innerfield : LIST<INT>>
LIST<STRUCT<innerfield : INT>>
DROP COLUMN <column_name> String
Drops the specified column. This action cannot be undone.
{ ALTER | MODIFY | CHANGE } COLUMN <old_name> <new_name> <data_type> String
Changes the data type for a column, and gives you the option to rename the column.
You can rename only columns of tables that are in scratch spaces and columns of Iceberg tables. If you do not want to rename the column, set <new_name> to <old_name>.
Only three types of changes to primitive types are allowed:
- INT to BIGINT
- FLOAT to DOUBLE
- DECIMAL(p, s) to DECIMAL(p', s), if you are widening the precision
You can alter columns that use complex types by using either of these two sets of syntax:
Set 1
- struct_type:
ROW( name primitive_or_complex_type, .. ) - list_type:
ARRAY(primitive_or_complex_type)
Examples:
ROW(innerfield INT, anotherinnerfield DOUBLE)
ARRAY(INT)
ROW(innerfield ARRAY(INT))
ARRAY(ROW(innerfield INT))
Set 2
- struct_type:
STRUCT <name : primitive_or_complex_type, ...> - list_type:
{ LIST | ARRAY } < primitive_or_complex_type >
Examples:
STRUCT<innerfield : INT, anotherinnerfield : DOUBLE>
LIST<INT>
ARRAY<INT>
STRUCT<innerfield : LIST<INT>>
LIST<STRUCT<innerfield : INT>>
MODIFY COLUMN <column_name> String
Specifies the column on which to either set a masking policy or unset one.
SET MASKING POLICY <function_name> ( <column_name> [, ... ] ) String
Sets a policy for masking data. The UDF serving as the masking policy must accept and return the same data type as the column it is masking. If a UDF with the given name does not exist, then the affected table will not be reachable until the policy is dropped or a UDF created.
UNSET MASKING POLICY <function_name> String
Removes a policy for masking data.
{ ADD | DROP } ROW ACCESS POLICY <function_name> ( <column_name> [ , ... ] ) String
Adds a row-access policy to the table, or removes one from the table. The UDF serving as the row-access policy must return BOOLEAN. If the UDF specified in the policy does not exist, then the Dremio engine gives an error when attempting to query the table.
LOCALSORT BY ( <column_name> [ , ... ] ) String Optional
The columns on which to sort new data that is added to the table after the ALTER TABLE command is run. When used in the reflection parameters, sorts the data that is in the reflection.
REFRESH METADATA
Refreshes the metadata associated with the specified table. You can choose to either do a full or partial metadata refresh. A full refresh will update the metadata for the entire table. A partial refresh will enable you to only update specified partitions. Optional clauses are available for refreshing a table's metadata. If you choose to use two or more of these clauses, they must be entered in a specified priority order:
- Promotion option: either
AVOID PROMOTIONorAUTO PROMOTION - Update option: either
FORCE UPDATEorLAZY UPDATE - Missing option: either
MAINTAIN WHEN MISSINGorDELETE WHEN MISSING
If the table is not partitioned, you will receive an error when you attempt to refresh the metadata using the FOR PARTITIONS clause.
FOR PARTITIONS ( <partition_name> = '<value>' ) String Optional
Use this clause to do a partial refresh of the table's metadata.
- The
<partition_name>identifies the name of the partition to be refreshed. - The
<value>identifies the specific partition that should be refreshed. Must be contained in single quotes.
{ AVOID | AUTO } PROMOTION Optional
Clauses that determine whether files and folders are promoted to datasets when you run a query.
The AVOID PROMOTION prevents queries from promoting files/folders to datasets. The AUTO PROMOTION allows queries to promote files/folders to datasets. This is the default option when you do not include a promotion clause.
{ FORCE | LAZY } UPDATE Optional
Clauses that determine whether metadata is updated when you run a query.
The FORCE UPDATE forces a full update of metadata. The LAZY UPDATE does not perform a full update of metadata. This is the default option when you do not include an update clause.
{ MAINTAIN | DELETE } WHEN MISSING Optional
Clauses that determine how missing metadata is handled when you run a query.
The MAINTAIN WHEN MISSING prevents missing metadata from being deleted during refresh. DELETE WHEN MISSING deletes missing metadata during refresh. This is the default option when you do not include a clause.
FORGET METADATA
Deletes the metadata information stored in Dremio for the specified table until the next metadata refresh. The dataset can still be queried using SQL.
SET TBLPROPERTIES ( '<property_name>' = '<property_value>' [ , ... ] )
Sets one or more table properties for controlling the behavior of the table. See Properties of Apache Iceberg Tables for a list of the supported properties.
UNSET TBLPROPERTIES ( '<property_name>' [ , ... ] )
Removes one or more table properties that control the behavior of the table. See Properties of Apache Iceberg Tables for a list of the supported properties.
CREATE AGGREGATE REFLECTION <reflection_name> String
Creates an aggregation reflection with the specified name.
DIMENSIONS ( <column_name> [ , ... ] ) String
The columns to include as dimensions in the reflection.
MEASURES ( <column_name> ( <aggregation_type> ) [ , ... ] ) String
The columns to include as measures in the reflection, and the type of aggregation to perform on them. The possible types are COUNT, MIN, MAX, SUM, and APPROXIMATE COUNT DISTINCT.
PARTITION BY ( { <column_name> | <partition_transform> } [ , ... ] ) String Optional
The columns or partition-transformation functions on which to partition the data horizontally in the reflection.
-
<column_name>: The unique name of the column. Multiple columns may be specified as long as the column names include their data type. Use commas to separate each column name and data-type pair. If a column is listed as a partition column, it cannot also be listed as a sort column for the same reflection. Each column specified must also be listed as a dimension column. -
<partition_transform>: Applies only to Iceberg tables. Use one of these partition-transformation functions:Type of Partition Transform Description identity(<column_name>) Creates one partition per value. This is the default transform. The column can use any supported data type. year(<column_name>) Partitions by year. The column must use the DATE or TIMESTAMP data type. month(<column_name>) Partitions by month. The column must use the DATE or TIMESTAMP data type. day(<column_name>) Partitions on the equivalent of dateint. The column must use the DATE or TIMESTAMP data type. hour(<column_name>) Partitions on the equivalent of dateint and hour. The column must use the TIMESTAMP data type. bucket(<integer>, <column_name>) Partitions data into the number of partitions specified by an integer. For example, if the integer value N is specified, the data is partitioned into N, or (0 to (N-1)), partitions. The partition in which an individual row is stored is determined by hashing the column value and then calculating <hash_value> mod N. If the result is 0, the row is placed in partition 0; if the result is 1, the row is placed in partition 1; and so on.
The column can use the DECIMAL, INT, BIGINT, VARCHAR, VARBINARY, DATE, or TIMESTAMP data type.truncate(<integer>, <column_name>) If the specified column uses the string data type, truncates strings to a maximum of the number of characters specified by an integer. For example, suppose the specified transform is truncate(1, stateUS). A value of CA is truncated to C, and the row is placed in partition C. A value of CO is also truncated to C, and the row is also placed in partition C.
If the specified column uses the integer or long data type, truncates column values in the following way: For any truncate(L, col), truncates the column value to the biggest multiple of L that is smaller than the column value. For example, suppose the specified transform is truncate(10, intColumn). A value of 1 is truncated to 0 and the row is placed in the partition 0. A value of 247 is truncated to 240 and the row is placed in partition 240. If the transform is truncate(3, intColumn), a value of 13 is truncated to 12 and the row is placed in partition 12. A value of 255 is not truncated, because it is divisble by 3, and the row is placed in partition 255.
The column can use the DECIMAL, INT, BIGINT, VARCHAR, or VARBINARY data type.
Note: The truncate transform does not change column values. It uses column values to calculate the correct partitions in which to place rows.
CREATE EXTERNAL REFLECTION <reflection_name> String
Creates an external reflection with the specified name.
USING <table_name> String
The path of the derived table to use with the external reflection.
CREATE RAW REFLECTION <reflection_name> String
Creates a raw reflection with the specified name.
USING DISPLAY ( <column_name1>, <column_name2>, ... ) String
The columns to include in the reflection.
DROP REFLECTION String Optional
Drops the specified reflection defined on the table.
REFRESH REFLECTIONS String Optional
For information about the refresh action performed, see Triggering Refreshes by Using the Reflection API, the Catalog API, or an SQL Command.
ROUTE REFLECTIONS TO { DEFAULT QUEUE | QUEUE { <queue_name> | <queue_uuid> } } String
Use the queue name or unique identifier to specify the queue on which to run jobs that create and refresh reflections that are defined on the table. If a queue name or unique identifier is not specified, the default queue is used. You can also directly specify the default queue.
{ ADD | DROP } PARTITION FIELD { <column_name> | <partition_transform> } String Optional
ADD partitions the table data on the values in a single column or by using one of the partition-transformation functions. DROP drops the partition definition.
<partition_transform>: Applies only to Iceberg tables. Use one of these partition-transformation functions:
| Transform | Description |
|---|---|
| identity( <col> ) | Explicitly specified identity transform |
| year( <col> ) | Partition by year. The column uses either the TIMESTAMP or DATE data type. |
| month( <ts_col> ) | Partition by month. The column uses either the TIMESTAMP or DATE data type. |
| day( <ts_col> ) | Partition by day. The column uses either the TIMESTAMP or DATE data type. |
| hour( <ts_col> ) | Partition by hour. The column uses the TIMESTAMP data type. |
| bucket( <count>, <col> ) | Partition by hashed value into <count> buckets |
| truncate( <length>, <col> ) | Partition by truncated value.
|
Examples
Add Primary Key for an Iceberg tableALTER TABLE services
ADD PRIMARY KEY (Country_ID);
ALTER TABLE customer1
ADD COLUMNS (SSN INT(9));
ALTER TABLE services
ADD COLUMNS (county varchar);
ALTER TABLE myTable
ADD COLUMNS (address VARCHAR);
ALTER TABLE customer1
DROP COLUMN SSN;
ALTER TABLE customer1
ALTER COLUMN SSN CHAR(11);
ALTER TABLE services
MODIFY COLUMN tip_amount tip_amount DECIMAL;
ALTER TABLE struct_type
MODIFY COLUMN a a struct<x: varchar, y: bigint>;
ALTER TABLE myTable
ALTER COLUMN id id BIGINT;
ALTER TABLE services
MODIFY COLUMN tip_amount gratuity_amount DECIMAL;
ALTER TABLE e.employees
MODIFY COLUMN ssn_col
SET MASKING POLICY protect_ssn (ssn_col, region);
ALTER TABLE e.employees
MODIFY COLUMN ssn_col
UNSET MASKING POLICY protect_ssn;
ALTER TABLE e.employees
ADD ROW ACCESS POLICY state_policy ( state_col );
ALTER TABLE employees
DROP ROW ACCESS POLICY state_policy (ssn_col, region);
ALTER TABLE customer1
REFRESH METADATA;
ALTER TABLE services
REFRESH METADATA;
ALTER TABLE services
REFRESH METADATA
AUTO PROMOTION
LAZY UPDATE
MAINTAIN WHEN MISSING;
ALTER TABLE customer1
REFRESH METADATA
FOR PARTITIONS ( "dir0" = 'a');
ALTER TABLE Samples."samples.dremio.com"."zips.json"
REFRESH METADATA
FOR PARTITIONS (state = 'TX');
ALTER TABLE Samples."samples.dremio.com"."zips.json"
REFRESH METADATA
FOR PARTITIONS (state = 'TX')
AUTO PROMOTION
LAZY UPDATE
MAINTAIN WHEN MISSING;
ALTER TABLE Samples."samples.dremio.com"."zips.json"
FORGET METADATA;
ALTER TABLE "@user1"."customers"
CREATE RAW REFLECTION customers_by_country USING
DISPLAY (id,lastName,firstName,address,country)
PARTITION BY (country)
LOCALSORT BY (lastName);
ALTER TABLE Samples."samples.dremio.com"."zips.json"
CREATE AGGREGATE REFLECTION per_state USING
DIMENSIONS (state)
MEASURES (city (COUNT))
LOCALSORT BY (state);
ALTER TABLE "Table 1"
ROUTE REFLECTIONS TO QUEUE "QUEUE 1";
ALTER TABLE "Table 2"
ROUTE REFLECTIONS TO QUEUE "QUEUE 1";
ALTER TABLE "Table 3"
ROUTE REFLECTIONS TO DEFAULT QUEUE;