CREATE TABLE AS

Description

Creates a table from the results of a query.

CREATE TABLE AS creates a table and fills it with data obtained using SELECT. The table columns have the names and data types associated with the output columns of SELECT (except that you can override the SELECT output column names by giving an explicit list of new column names).

CREATE TABLE AS queries a source table once and writes the data in a new table. The result in the query view changes with the source table. In contrast, the view re-computes and defines its SELECT statement at each query.

Precautions

This statement cannot be used to create a partitioned table.
If an error occurs during table creation, after it is fixed, the system may fail to delete the disk files that are created before the last automatic clearance and whose size is not 0. This problem seldom occurs and does not affect system running of the database.

Syntax

    
         CREATE [ [ GLOBAL | LOCAL ] [ TEMPORARY | TEMP ] | UNLOGGED ] TABLE [ IF NOT EXISTS ] table_name
    [ (column_name [, ...] ) ]
    [ WITH ( {storage_parameter = value} [, ... ] ) ]
    [ COMPRESS | NOCOMPRESS ]
    [ TABLESPACE tablespace_name ]
    [ DISTRIBUTE BY { REPLICATION | HASH ( column_name [, ...] ) 
    | RANGE ( column_name [, ...] ) { SLICE REFERENCES tablename | ( slice_less_than_item [, ...] )
    | ( slice_start_end_item [, ...] ) }
    | LIST ( column_name [, ...] ) { SLICE REFERENCES tablename | ( slice_values_item [, ...] ) }
    } ]
    [ TO { GROUP groupname | NODE ( nodename [, ... ] ) } ]
    AS query
    [ WITH [ NO ] DATA ];

For details about each field, see Syntax.

Parameters

UNLOGGED
Specifies that the table is created as an unlogged table. Data written to unlogged tables is not written to the WALs, which makes them considerably faster than ordinary tables. However, they are not crash-safe. An unlogged table is automatically truncated after a crash or unclean shutdown. The contents of an unlogged table are also not replicated to standby servers. Any indexes created on an unlogged table are automatically unlogged as well.
- Usage scenario: Unlogged tables do not ensure data security. Users can back up data before using unlogged tables; for example, users should back up the data before a system upgrade.
- Troubleshooting: If data is missing in the indexes of unlogged tables due to some unexpected operations such as an unclean shutdown, users should rebuild the indexes with errors.
GLOBAL | LOCAL
When creating a temporary table, you can specify the GLOBAL or LOCAL keyword before TEMP or TEMPORARY. Currently, the two keywords are used to be compatible with the SQL standard. A local temporary table will be created by the GaussDB regardless of whether GLOBAL or LOCAL is specified.
TEMPORARY | TEMP
If TEMP or TEMPORARY is specified, the created table is a temporary table. A temporary table is automatically dropped at the end of the current session. Therefore, you can create and use temporary tables in the current session as long as the connected CN in the session is normal. Temporary tables are created only in the current session. If a DDL statement involves operations on temporary tables, a DDL error will be generated. Therefore, you are advised not to perform operations on temporary tables in DDL statements. TEMP is equivalent to TEMPORARY.
- Temporary tables are visible to the current session through the schema starting with pg_temp start. Users should not delete schema started with pg_temp or pg_toast_temp.
- If TEMPORARY or TEMP is not specified when you create a table but its schema is set to that starting with pg_temp_ in the current session, the table will be created as a temporary table.
- A temporary table is visible only to the current session. Therefore, it cannot be used together with \parallel on.
- Temporary tables do not support DN faults or primary/standby switchovers.
table_name
Specifies the name of the table to be created.

Value range: a string. It must comply with the naming convention.
column_name
Specifies the name of a column to be created in the new table.

Value range: a string. It must comply with the naming convention.
WITH ( storage_parameter [= value] [, ... ] )
Specifies an optional storage parameter for a table or an index. See details of parameters below.
- FILLFACTOR
  The fill factor of a table is a percentage from 10 to 100. 100 (complete filling) is the default value. If the Ustore storage engine is used, the default value is 92. When a smaller fill factor is specified, INSERT operations fill table pages only to the indicated percentage. The remaining space on each page is reserved for updating rows on that page. This gives UPDATE a chance to place the updated copy of a row on the same page, which is more efficient than placing it on a different page. For a table whose entries are never updated, setting the fill factor to 100 (complete filling) is the best choice, but in heavily updated tables a smaller fill factor would be appropriate.
  
  Value range: 10–100
- ORIENTATION
  Value range:
  
  ROW (default value): The data will be stored in rows.
- COMPRESSION
  Specifies the compression level of table data. It determines the compression ratio and time. Generally, the higher the level of compression, the higher the ratio, the longer the time; and the lower the level of compression, the lower the ratio, the shorter the time. The actual compression ratio depends on the distribution mode of table data loaded.
  
  Value range:
  
  Row-store tables do not support compression.
COMPRESS / NOCOMPRESS
Specifies keyword COMPRESS during the creation of a table, so that the compression feature is triggered in case of bulk INSERT operations. If this feature is enabled, a scan is performed for all tuple data within the page to generate a dictionary and then the tuple data is compressed and stored. If NOCOMPRESS is specified, the table is not compressed. Row-store tables do not support compression.

Default value: NOCOMPRESS, that is, tuple data is not compressed before storage.
TABLESPACE tablespace_name
Specifies that the new table will be created in the tablespace_name tablespace. If not specified, the default tablespace is used.
DISTRIBUTE BY
For details, see DISTRIBUTE BY.
TO { GROUP groupname | NODE ( nodename [, ... ] ) }
TO GROUP specifies the node group to which the table to be created belongs. TO NODE is used for internal scale-out tools.
AS query
Specifies a SELECT or VALUES command, or an EXECUTE command that runs a prepared SELECT or VALUES query.
[ WITH [ NO ] DATA ]
Specifies whether the data produced by the query should be copied to the new table. By default, the data will be copied. If the value NO is used, only the table structure will be copied.

Examples

    
         -- Create a schema.
gaussdb=# CREATE SCHEMA tpcds;

-- Create the tpcds.store_returns table.
gaussdb=# CREATE TABLE tpcds.store_returns
(
    W_WAREHOUSE_SK            INTEGER               NOT NULL,
    W_WAREHOUSE_ID            CHAR(16)              NOT NULL,
    sr_item_sk                VARCHAR(20)                   ,
    W_WAREHOUSE_SQ_FT         INTEGER                       
);

-- Insert a record into a table:
gaussdb=# INSERT INTO tpcds.store_returns(W_WAREHOUSE_SK, W_WAREHOUSE_ID, sr_item_sk, W_WAREHOUSE_SQ_FT) VALUES (1, 'AAAAAAAABAAAAAAA', '4800', '20');

-- Create the tpcds.store_returns_t1 table and insert numbers that are greater than 4795 in the sr_item_sk column of the tpcds.store_returns table.
gaussdb=# CREATE TABLE tpcds.store_returns_t1 AS SELECT * FROM tpcds.store_returns WHERE sr_item_sk > '4795';

-- Copy tpcds.store_returns to create the tpcds.store_returns_t2 table.
gaussdb=# CREATE TABLE tpcds.store_returns_t2 AS table tpcds.store_returns;

-- Delete the table.
gaussdb=# DROP TABLE tpcds.store_returns_t1 ;
gaussdb=# DROP TABLE tpcds.store_returns_t2 ;
gaussdb=# DROP TABLE tpcds.store_returns;

-- Delete the schema.
gaussdb=# DROP SCHEMA tpcds CASCADE;