OpenText Analytics Database 26.2.x – Creating a table from other tables

Admin: Replicating a table

Mon, 01 Jan 0001 00:00:00 +0000

You can create a table from an existing one using CREATE TABLE with the LIKE clause:

CREATE TABLE [ IF NOT EXISTS ] [[ { namespace. | database. } ]schema.]table
LIKE [[ { namespace. | database. } ]schema.]existing-table
  [ { INCLUDING | EXCLUDING } PROJECTIONS ]
  [ { INCLUDE | EXCLUDE } [SCHEMA] PRIVILEGES ]

Creating a table with LIKE replicates the source table definition and any storage policy associated with it. Table data and expressions on columns are not copied to the new table.

The user performing the operation owns the new table.

The source table cannot have out-of-date projections and cannot be a temporary table.

Copying constraints

CREATE TABLE LIKE copies all table constraints except for:

Foreign key constraints.
Sequence column constraints.

For any column that obtains its values from a sequence, including IDENTITY columns, the database copies the column values into the new table, but removes the original constraint. For example, the following table definition sets an IDENTITY constraint on the ID column:

=> CREATE TABLE public.Premium_Customer
  (
    ID IDENTITY,
    lname varchar(25),
    fname varchar(25),
    store_membership_card int
  );

The following CREATE TABLE LIKE statement uses the source table Premium_Customer to create the replica All_Customers. The database removes the IDENTITY constraint, changing the column to an integer column with a NOT NULL constraint:

=> CREATE TABLE All_Customers LIKE Premium_Customer;
   CREATE TABLE

=> SELECT export_tables('','All_Customers');
                   export_tables
---------------------------------------------------
CREATE TABLE public.All_Customers
(
    ID int NOT NULL,
    lname varchar(25),
    fname varchar(25),
    store_membership_card int
);
(1 row)

Including projections

You can qualify the LIKE clause with INCLUDING PROJECTIONS or EXCLUDING PROJECTIONS, which specify whether to copy projections from the source table:

EXCLUDING PROJECTIONS (default): Do not copy projections from the source table.
INCLUDING PROJECTIONS: Copy current projections from the source table. The database names the new projections according to its naming conventions, to avoid name conflicts with existing objects.

Including schema privileges

You can specify default inheritance of schema privileges for the new table:

EXCLUDE [SCHEMA] PRIVILEGES (default) disables inheritance of privileges from the schema
INCLUDE [SCHEMA] PRIVILEGES grants the table the same privileges granted to its schema

For more information see Setting privilege inheritance on tables and views.

Examples

Create the table states:

=> CREATE TABLE states (
     state char(2) NOT NULL, bird varchar(20), tree varchar (20), tax float, stateDate char (20))
     PARTITION BY state;

Populate the table with data:

INSERT INTO states VALUES ('MA', 'chickadee', 'american_elm', 5.675, '07-04-1620');
INSERT INTO states VALUES ('VT', 'Hermit_Thrasher', 'Sugar_Maple', 6.0, '07-04-1610');
INSERT INTO states VALUES ('NH', 'Purple_Finch', 'White_Birch', 0, '07-04-1615');
INSERT INTO states VALUES ('ME', 'Black_Cap_Chickadee', 'Pine_Tree', 5, '07-04-1615');
INSERT INTO states VALUES ('CT', 'American_Robin', 'White_Oak', 6.35, '07-04-1618');
INSERT INTO states VALUES ('RI', 'Rhode_Island_Red', 'Red_Maple', 5, '07-04-1619');

View the table contents:

=> SELECT * FROM states;
 state |        bird         |     tree     |  tax  |      stateDate
-------+---------------------+--------------+-------+----------------------
 VT    | Hermit_Thrasher     | Sugar_Maple  |     6 | 07-04-1610
 CT    | American_Robin      | White_Oak    |  6.35 | 07-04-1618
 RI    | Rhode_Island_Red    | Red_Maple    |     5 | 07-04-1619
 MA    | chickadee           | american_elm | 5.675 | 07-04-1620
 NH    | Purple_Finch        | White_Birch  |     0 | 07-04-1615
 ME    | Black_Cap_Chickadee | Pine_Tree    |     5 | 07-04-1615
(6 rows

Create a sample projection and refresh:

=> CREATE PROJECTION states_p AS SELECT state FROM states;

=> SELECT START_REFRESH();

Create a table like the states table and include its projections:

=> CREATE TABLE newstates LIKE states INCLUDING PROJECTIONS;

View projections for the two tables. The database has copied projections from states to newstates:

=> \dj
                                                      List of projections
            Schema             |                   Name                    |  Owner  |       Node       | Comment
-------------------------------+-------------------------------------------+---------+------------------+---------
 public                        | newstates_b0                              | dbadmin |                  |
 public                        | newstates_b1                              | dbadmin |                  |
 public                        | newstates_p_b0                            | dbadmin |                  |
 public                        | newstates_p_b1                            | dbadmin |                  |
 public                        | states_b0                                 | dbadmin |                  |
 public                        | states_b1                                 | dbadmin |                  |
 public                        | states_p_b0                               | dbadmin |                  |
 public                        | states_p_b1                               | dbadmin |                  |

Query the new table:

=> SELECT * FROM newstates;
 state | bird | tree | tax | stateDate
-------+------+------+-----+-----------
(0 rows)

When you use the CREATE TABLE LIKE statement, storage policy objects associated with the table are also copied. Data added to the new table use the same labeled storage location as the source table, unless you change the storage policy. For more information, see Working With Storage Locations.

Admin: Creating a table from a query

Mon, 01 Jan 0001 00:00:00 +0000

CREATE TABLE can specify an AS clause to create a table from query results, as in the following example:

=> CREATE TABLE cust_basic_profile AS SELECT
     customer_key, customer_gender, customer_age, marital_status, annual_income, occupation
   FROM customer_dimension WHERE customer_age>18 AND customer_gender !='';
CREATE TABLE

=> SELECT customer_age, annual_income, occupation 
   FROM cust_basic_profile
   WHERE customer_age > 23 ORDER BY customer_age;
 customer_age | annual_income |     occupation
--------------+---------------+--------------------
           24 |        469210 | Hairdresser
           24 |        140833 | Butler
           24 |        558867 | Lumberjack
           24 |        529117 | Mechanic
           24 |        322062 | Acrobat
           24 |        213734 | Writer
           ...

Labeling the AS clause

You can embed a LABEL hint in an AS clause in two places:

Immediately after the AS keyword:

=> CREATE TABLE myTable AS /*+LABEL myLabel*/ ...

In the SELECT statement:

=> CREATE TABLE myTable AS SELECT /*+LABEL myLabel*/ ...

If the AS clause contains labels in both places, the first label has precedence.

Labels are invalid for external tables.

Loading historical data

You can specify that the query return historical data by adding AT followed by one of:

EPOCH LATEST: Return data up to but not including the current epoch. The result set includes data from the latest committed DML transaction.
EPOCH integer: Return data up to and including the specified epoch.
TIME 'timestamp': Return data from the epoch at the specified timestamp.

These options are ignored if used to query temporary or external tables.

See Epochs for additional information about how OpenText™ Analytics Database uses epochs.

Zero-width column handling

If the query returns a column with zero width, the database automatically converts it to a VARCHAR(80) column. For example:

=> CREATE TABLE example AS SELECT '' AS X;
CREATE TABLE

=> SELECT EXPORT_TABLES ('', 'example');
                       EXPORT_TABLES
----------------------------------------------------------
CREATE TABLE public.example
(
    X varchar(80)
);

Requirements and restrictions

If you create a temporary table from a query, you must specify ON COMMIT PRESERVE ROWS in order to load the result set into the table. Otherwise, the database creates an empty table.
If the query output has expressions other than simple columns, such as constants or functions, you must specify an alias for each expression, or list all columns in the column name list.
You cannot use CREATE TABLE AS SELECT with a SELECT that returns values of complex types. You can, however, use CREATE TABLE LIKE.