How to Determine Most Recent Record in Child Table Using Timestamps and Indexing Strategies

Efficiently Determining Most Recent Record in Child Table

As a developer, it’s essential to optimize queries and improve performance. In this article, we’ll explore an efficient method for determining the most recent record in a child table based on the created_timestamp. We’ll discuss various approaches, including indexing strategies.

Problem Statement

We’re working on a project that involves versioned entities. The constant values are stored in a parent table (entity), and the varying values are stored in a child “version” table (entity_version) with its own key and a foreign key to the parent table. We need to compute the most recent version for each entity based on the created_timestamp. However, we’re using an outdated approach that relies on the maximum version_id instead of the latest created_timestamp.

SQL Schema

The provided SQL Fiddle schema illustrates the relationships between the tables:

CREATE TABLE entity (
    entity_id INTEGER,
    constant_value VARCHAR2(50) NOT NULL,
    CONSTRAINT pk_entity PRIMARY KEY (entity_id)
);

CREATE SEQUENCE seq_entity;

CREATE TABLE entity_version (
    entity_id INTEGER,
    version_id INTEGER,
    varying_value VARCHAR2(50) NULL,
    created_timestamp TIMESTAMP (9) WITH TIME ZONE DEFAULT systimestamp NOT NULL,
    CONSTRAINT pk_entity_version PRIMARY KEY (version_id),
    CONSTRAINT fk_entity_id FOREIGN KEY (entity_id) REFERENCES entity(entity_id)
);

CREATE SEQUENCE seq_entity_version;

CREATE INDEX idx_fk_entity_id ON entity_version(entity_id);

Querying the Most Recent Record

The provided query joins entity, v_entity_curr_version, and entity_version to retrieve the most recent record:

SELECT e.constant_value,
       ev.varying_value
FROM entity e
JOIN v_entity_curr_version ecv
  ON ecv.entity_id = e.entity_id
JOIN entity_version ev
  ON ev.entity_id = ecv.entity_id AND ev.version_id = ecv.version_id;

This query returns the constant value and varying value for each entity.

Computing Most Recent Version ID

The provided function fn_get_max_version computes a single most recent version id:

FUNCTION fn_get_max_version(p_entity_id INTEGER) RETURN INTEGER IS
    v_version_id entity_version.version_id%TYPE;
BEGIN
    SELECT ev.version_id
      INTO v_version_id
      FROM entity_version ev
     WHERE ev.entity_id = p_entity_id
     ORDER BY ev.created_timestamp DESC
     FETCH FIRST ROW ONLY;

    -- return to caller
    RETURN v_version_id;
END;

This function returns the most recent version id for a given entity_id.

Indexing Strategies

To improve query performance, we need to analyze indexing strategies.

1. Creating a Unique Index on Entity Version

The recommended indexing strategy involves creating a unique index on the combined columns (entity_id and version_id) in descending order of version_id. This ensures that the optimizer can use an index to retrieve the most recent record:

CREATE UNIQUE INDEX ENTITY_VERSION_INDEX1 ON ENTITY_VERSION 
(entity_id ASC, version_id DESC);

By creating this unique index, we enable the optimizer to efficiently scan the entity_version table and retrieve the most recent record based on the created_timestamp.

2. Analyzing Explain Plans

Before and after applying the indexing strategy, analyze the explain plans to verify that the optimizer is using the index:

-- Before indexing
SELECT * FROM entity_version ev 
WHERE ev.entity_id = :p_entity_id 
ORDER BY ev.created_timestamp DESC 
FETCH FIRST ROW ONLY;

-- After indexing
SELECT * FROM entity_version ev 
WHERE ev.entity_id = :p_entity_id 
AND ev.version_id = (SELECT MAX(version_id) 
                     FROM entity_version ev 
                     WHERE ev.entity_id = :p_entity_id 
                     ORDER BY ev.created_timestamp DESC)

Verify that the explain plan includes the index range scan (INDEX RANGE SCAN ENTITY_VERSION_INDEX1) after applying the indexing strategy.

Conclusion

In conclusion, we’ve explored an efficient method for determining the most recent record in a child table based on the created_timestamp. By creating a unique index on the combined columns (entity_id and version_id) in descending order of version_id, we enable the optimizer to efficiently retrieve the most recent record. Additionally, analyzing explain plans before and after applying the indexing strategy ensures that the optimizer is using the index correctly.

Example Use Cases

Retrieve Most Recent Record: Use the optimized query:

SELECT e.constant_value,
       ev.varying_value
FROM entity e
JOIN v_entity_curr_version ecv 
  ON ecv.entity_id = e.entity_id
JOIN entity_version ev 
  ON ev.entity_id = ecv.entity_id AND ev.version_id = ecv.version_id;

Compute Most Recent Version ID: Use the optimized function:

FUNCTION fn_get_max_version(p_entity_id INTEGER) RETURN INTEGER IS
    v_version_id entity_version.version_id%TYPE;
BEGIN
    SELECT ev.version_id
      INTO v_version_id
      FROM entity_version ev
     WHERE ev.entity_id = p_entity_id
     ORDER BY ev.created_timestamp DESC
     FETCH FIRST ROW ONLY;

    -- return to caller
    RETURN v_version_id;
END;

Indexing Strategy: Create the unique index:

CREATE UNIQUE INDEX ENTITY_VERSION_INDEX1 ON ENTITY_VERSION 
(entity_id ASC, version_id DESC);

By following these guidelines and best practices, you can efficiently determine the most recent record in a child table based on the created_timestamp.

Last modified on 2024-12-26