16.6.2 Feature Support by Table Type

Machbase provides five table types for different uses. Each supports features according to its design goals.

Table Type Overview

Table Type	Primary Use
TAG	High-speed time-series sensor ingestion and aggregation (ROLLUP)
LOG	Sequential storage of logs/events in defined columns and text search
LOOKUP	Metadata, code tables, and reference data (supports UPDATE/DELETE)
VOLATILE	In-memory server state and caches; data is lost on restart
TRANSACTION	General relational data requiring transactions

Feature Support Matrix

Feature	TAG	LOG	LOOKUP	VOLATILE	TRANSACTION
Writes
INSERT (SQL)	O	O	O	O	O
Updates/Deletes
UPDATE	△	X	O	O	O
DELETE	O	O	O	O	O
Transactions
Transaction (COMMIT/ROLLBACK)	X	X	X	X	O
Aggregation and Search
ROLLUP	O	X	X	X	X
Text search (KEYWORD INDEX)	X	O	X	X	X
JSON
JSON columns	O	O	O	X	O
JSON path query	O	O	O	X	O
Fixed-point Numbers
DECIMAL / NUMERIC columns	O	O	O	O	O
Fixed-length ARRAY
ARRAY column creation	O	O	O	O	O
ARRAY ADD/DROP COLUMN	△	O	O	O	O
Indexes
Default indexes	O	O	O	O	O
LSM indexes	X	O	X	X	X
Queries
SELECT	O	O	O	O	O
Latest-value queries (`SCAN_BACKWARD`, TAG stat)	O	X	X	X	X
JOIN (with other tables)	△	△	O	O	O
Subquery	O	O	O	O	O
VIEW	O	O	O	O	O

Symbols: O = supported, X = not supported, △ = partially supported or constrained

Append support by table type depends on the client API. For the language and API you use, check the SDK Append Support Matrix.

DECIMAL is an exact fixed-point type available in all five table types. NUMERIC, DEC, FIXED, and NUMBER are aliases for DECIMAL. Maximum precision is 65 and maximum scale is 30. For details, see DECIMAL and NUMERIC Fixed-point Types.

ARRAY ADD/DROP is supported for LOG, VOLATILE, LOOKUP, TRANSACTION, and TAG METADATA in Standard Edition. The TAG column’s △ means that ALTER supports TAG METADATA only; ordinary TAG DATA columns cannot be added. Cluster Edition supports only the LOG path. For exact syntax and DEFAULT rules for existing rows, see DDL Syntax and Numeric ARRAY Types.

Main Constraints

TAG Table UPDATE Constraints (△, Standard Edition)

TAG table UPDATE must satisfy all of the following conditions.

TAG data UPDATE is not available in Cluster Edition.

Include a tag selection predicate (name =, name IN, or name LIKE) in WHERE
Include a BASETIME column predicate in WHERE
SET targets must be actual data columns
Data UPDATE cannot modify time (BASETIME), name, or metadata columns
SET right-hand expressions cannot reference existing row columns; use constants, binds, or column-free expressions

-- Allowed: update a data column using tag and time predicates
UPDATE sensor_data
   SET value = 101
 WHERE name = 'sensor01'
   AND time >= TO_DATE('2026-07-01', 'YYYY-MM-DD');

-- Not allowed: update the BASETIME column
UPDATE sensor_data
   SET time = SYSDATE
 WHERE name = 'sensor01'
   AND time >= TO_DATE('2026-07-01', 'YYYY-MM-DD');

For details, see TAG Data UPDATE Support.

Transaction Scope of LOOKUP and VOLATILE

Each DML statement on LOOKUP and VOLATILE tables is applied independently. These tables do not participate in TRANSACTION table transactions grouping multiple statements with BEGIN and COMMIT/ROLLBACK.

JSON Column Support

JSON columns are supported in TAG, LOG, LOOKUP, and TRANSACTION tables. VOLATILE does not support JSON columns. LOOKUP JSON columns can be ordinary columns but cannot be primary keys. See JSON Support by Table Type.

TAG Latest-value and Time-range Queries

TAG tables use reverse scans and time predicates to query recent values and time ranges.

-- Query the five latest values for a specific tag
SELECT /*+ SCAN_BACKWARD(sensor_data) */ *
  FROM sensor_data
 WHERE name = 'sensor01'
 LIMIT 5;

-- Query a time range
SELECT * FROM sensor_data
WHERE name = 'sensor01'
  AND time BETWEEN TO_DATE('2024-01-01') AND TO_DATE('2024-01-02');

Last updated on Sep 9, 2026

16.6.1 Feature Support by Edition 16.6.3 TRANSACTION Feature Support