13 Managing Tables & Regions

You will first create a sample table. Then you will learn different ways to alter the table. At the end of the section, you will drop the table. You will also learn to view the existing regions and drop a particular region.

Start your KVSTORE or KVLite and open the SQL shell.
java -jar lib/kvstore.jar kvlite -secure-config disable
java -jar lib/sql.jar -helper-hosts localhost:5000 -store kvstore

Alter Table

You can use the alter table command to perform the following operations.
  • Add schema fields to the table schema
  • Remove schema fields from the table schema
  • Add a region
  • Remove a region
  • Modify the Time-To-Live value of the table

Note:

You can specify only one type of operation in a single command. For example, you cannot remove a schema field and set the TTL value together.
Create a sample table :
CREATE TABLE demo_acct(
acct_id INTEGER,
acct_data JSON, 
PRIMARY KEY(acct_id)
)
Example 1: Add schema field to the table schema.
ALTER TABLE demo_acct(ADD acct_balance INTEGER)

Explanation: Adding a field does not affect the existing rows in the table. If a field is added, its default value or NULL will be used as the value of this field in existing rows that do not contain it. The field to add maybe a top-level field (i.e. A table column) or it may be deeply nested inside a hierarchical table schema. As a result, the field is specified via a path.

Example 2: Remove schema fields in the table schema.
ALTER TABLE demo_acct(DROP acct_balance)
Explanation: You can drop any field in the schema other than the primary key. If you try removing the primary key field, you get an error as shown below.
ALTER TABLE demo_acct(DROP acct_id)
Output( showing error):
Error handling command ALTER TABLE demo_acct(DROP acct_id):
Error: at (1, 27) Cannot remove a primary key field: acct_id

Example 3: Add a region

The add regions clause lets you link an existing Multi-Region Table (MR Table) with new regions in a multi-region Oracle NoSQL Database environment. You use this clause to expand MR Tables to new regions.

Associate a new region with an existing MR Table using the DDL command shown below.
ALTER TABLE <table_name> ADD REGIONS <region_name>

Explanation: Here, table_name is an MR table and region_name is an existing region.

Example 4: Remove a region

The drop regions clause lets you disconnect an existing MR Table from a participating region in a multi-region Oracle NoSQL Database environment. You use this clause to contract MR Tables to fewer regions.

To remove an MR Table from a specific region in a Multi-Region NoSQL Database setup, you must run the following steps from all the other participating regions.
ALTER TABLE <table_name> DROP REGIONS <comma_separated_list_of_regions>

Here, table_name is a MR Table and comma_separated_list_of_regions is a list of regions to be dropped.

Example 5: Modify the Time-To-Live value of the table

Time-to-Live (TTL) is a mechanism that allows you to set a time frame on table rows, after which the rows expire automatically, and are no longer available. By default, every table that you create has a TTL value of zero, indicating that it has no expiration time.

You can use ALTER TABLE command to change this value for any table. You can specify the TTL with a number, followed by either HOURS or DAYS.
ALTER TABLE demo_acct USING TTL 5 days

Note:

Altering the TTL value for a table does not change the TTL value for existing rows in the table. Rather, it will only change the default TTL value placed in rows created subsequent to the alter table. To modify the TTL of every record in a table, you must iterate through each record of the table and update its TTL value.

Drop Table

The drop table statement removes the specified table and all its associated indexes from the database. By default, if the named table does not exist then this statement fails. You don't get an error if the optional IF EXISTS clause is specified and the table does not exist.
DROP TABLE demo_acct

Note:

To drop a MR Table, first drop all of its child tables. Otherwise, the DROP statement results in an error.

Manage regions

The show regions statement provides the list of regions present in the Multi-Region Oracle NoSQL Database. You need to specify "AS JSON" if you want the output to be in JSON format.

Example 1: The following statement lists all the existing regions.
SHOW REGIONS
The following statement lists all the existing regions in JSON format.
SHOW AS JSON REGIONS
In a Multi-Region Oracle NoSQL Database environment, the drop region statement removes the specified remote region from the local region. See Set up Multi-Region Environment for more details on the local regions and remote regions in a Multi-Region setup.

Note:

This region must be different from the local region where the command is executed.
The following drop region statement removes a remote region named my_region1.
DROP REGION my_region1