CREATE TABLE AS

Defines a new table from the results of a query.

Synopsis

CREATE [ [GLOBAL | LOCAL] {TEMPORARY | TEMP} ] TABLE <table_name>
   [(<column_name> [, ...] )]
   [ WITH ( storage_parameter=<value> [, ... ] )
   [ON COMMIT {PRESERVE ROWS | DELETE ROWS | DROP}]
   [TABLESPACE <tablespace>]
   AS <query>
   [DISTRIBUTED BY (<column>, [ ... ] ) | DISTRIBUTED RANDOMLY]

where <storage_parameter> is:

   APPENDONLY={TRUE}
   BLOCKSIZE={8192-2097152} 
   bucketnum={<x>}
   ORIENTATION={ROW | PARQUET}
   COMPRESSTYPE={ZLIB | SNAPPY | GZIP | NONE}
   COMPRESSLEVEL={0-9 | 1}
   FILLFACTOR={10-100}
   OIDS=[TRUE | FALSE]
   PAGESIZE={1024-1073741823}
   ROWGROUPSIZE={1024-1073741823}

Description

CREATE TABLE AS creates a table and fills it with data computed by a SELECT command. The table columns have the names and data types associated with the output columns of the SELECT, however you can override the column names by giving an explicit list of new column names.

CREATE TABLE AS creates a new table and evaluates the query just once to fill the new table initially. The new table will not track subsequent changes to the source tables of the query.

Parameters

GLOBAL | LOCAL

These keywords are present for SQL standard compatibility, but have no effect in HAWQ.

TEMPORARY | TEMP

If specified, the new table is created as a temporary table. Temporary tables are automatically dropped at the end of a session, or optionally at the end of the current transaction (see ON COMMIT). Existing permanent tables with the same name are not visible to the current session while the temporary table exists, unless they are referenced with schema-qualified names. Any indexes created on a temporary table are automatically temporary as well.

<table_name>

The name (optionally schema-qualified) of the new table to be created.

<column_name>

The name of a column in the new table. If column names are not provided, they are taken from the output column names of the query. If the table is created from an EXECUTE command, a column name list cannot be specified.

WITH (<storage_parameter>=<value> )

The WITH clause can be used to set storage options for the table or its indexes. Note that you can also set different storage parameters on a particular partition or subpartition by declaring the WITH clause in the partition specification. The following storage options are available:

APPENDONLY — Set to TRUE to create the table as an append-only table. If FALSE, an error message displays stating that heap tables are not supported.

BLOCKSIZE — Set to the size, in bytes for each block in a table. The BLOCKSIZE must be between 8192 and 2097152 bytes, and be a multiple of 8192. The default is 32768.

bucketnum — Set to the number of hash buckets to be used in creating a hash-distributed table. If changing the number of hash buckets, use WITH to specify bucketnum in creating a hash-distributed table. If distribution is specified by column, the table will inherit the value.

ORIENTATION — Set to row (the default) for row-oriented storage, or parquet. This option is only valid if APPENDONLY=TRUE. Heap-storage tables can only be row-oriented.

COMPRESSTYPE — Set to ZLIB, SNAPPY, or GZIP to specify the type of compression used. ZLIB provides more compact compression ratios at lower speeds. Parquet tables support SNAPPY and GZIP compression. Append-only tables support SNAPPY and ZLIB compression. This option is valid only if APPENDONLY=TRUE.

COMPRESSLEVEL — Set to an integer value from 1 (fastest compression) to 9 (highest compression ratio). If not declared, the default is 1. This option is valid only if APPENDONLY=TRUE and COMPRESSTYPE=[ZLIB|GZIP].

OIDS — Set to OIDS=FALSE (the default) so that rows do not have object identifiers assigned to them. Do not enable OIDS when creating a table. On large tables, such as those in a typical HAWQ system, using OIDs for table rows can cause wrap-around of the 32-bit OID counter. Once the counter wraps around, OIDs can no longer be assumed to be unique, which not only makes them useless to user applications, but can also cause problems in the HAWQ system catalog tables. In addition, excluding OIDs from a table reduces the space required to store the table on disk by 4 bytes per row, slightly improving performance.

ON COMMIT

The behavior of temporary tables at the end of a transaction block can be controlled using ON COMMIT. The three options are:

PRESERVE ROWS — No special action is taken at the ends of transactions for temporary tables. This is the default behavior.

DELETE ROWS — All rows in the temporary table will be deleted at the end of each transaction block. Essentially, an automatic TRUNCATE is done at each commit.

DROP — The temporary table will be dropped at the end of the current transaction block.

TABLESPACE <tablespace>

The tablespace is the name of the tablespace in which the new table is to be created. If not specified, the database’s default tablespace is used.

AS <query>

A SELECT command, or an EXECUTE command that runs a prepared SELECT query.

DISTRIBUTED BY (<column>, [ … ] )
DISTRIBUTED RANDOMLY

Used to declare the HAWQ distribution policy for the table. The default is RANDOM distribution. DISTIBUTED BY can use hash distribution with one or more columns declared as the distribution key. If hash distribution is desired, it can be specified using bucketnum attribute, using the first eligible column of the table as the distribution key.

Notes

This command is functionally similar to SELECT INTO, but it is preferred since it is less likely to be confused with other uses of the SELECT INTO syntax. Furthermore, CREATE TABLE AS offers a superset of the functionality offered by SELECT INTO.

CREATE TABLE AS can be used for fast data loading from external table data sources. See CREATE EXTERNAL TABLE.

Examples

Create a new table films_recent consisting of only recent entries from the table films:

CREATE TABLE films_recent AS SELECT * FROM films WHERE 
date_prod >= '2007-01-01';

Create a new temporary table films_recent, consisting of only recent entries from the table films, using a prepared statement. The new table has OIDs and will be dropped at commit:

PREPARE recentfilms(date) AS SELECT * FROM films WHERE 
date_prod > $1;
CREATE TEMP TABLE films_recent WITH (OIDS) ON COMMIT DROP AS 
EXECUTE recentfilms('2007-01-01');

Compatibility

CREATE TABLE AS conforms to the SQL standard, with the following exceptions:

• The standard requires parentheses around the subquery clause; in HAWQ, these parentheses are optional.
• The standard defines a WITH [NO] DATA clause; this is not currently implemented by HAWQ. The behavior provided by HAWQ is equivalent to the standard’s WITH DATA case. WITH NO DATA can be simulated by appending LIMIT 0 to the query.
• HAWQ handles temporary tables differently from the standard; see CREATE TABLE for details.
• The WITH clause is a HAWQ extension; neither storage parameters nor OIDs are in the standard.
• The HAWQ concept of tablespaces is not part of the standard. The TABLESPACE clause is an extension.

See Also

CREATE EXTERNAL TABLE, EXECUTE, SELECT, SELECT INTO