How to query a json column for empty objects?

sql

json

indexing

performance

byAnton Shumikhin·Aug 4, 2024

To find an empty JSON object in your DB, get straight to the point and pile into your SQL query with JSON_LENGTH in a WHERE clause:

SELECT * FROM your_table WHERE JSON_LENGTH(json_column) = 0;

This query will happily return rows with {} in json_column.

Knowing the ropes: JSON in SQL

Understanding JSON in SQL, its types, and manipulation methods will save you from throwing your keyboard out the window. In PostgreSQL, you've got to pick one side of the fence - json or jsonb. While json stores an exact text copy, jsonb stores structured, index-friendly binary format.

The magic wand: jsonb

To cast your json into jsonb for efficient, smooth querying:

SELECT * FROM your_table WHERE json_column::jsonb = '{}';

The sneaky peak: JSON Data type

json_typeof(json_column) helps you determine if the column has an empty JSON:

SELECT * FROM your_table WHERE json_typeof(json_column) = 'object' AND json_column::jsonb = '{}';

The charming spell: Cast and Compare

You could turn your JSON into text:

SELECT * FROM your_table WHERE TRIM(json_column::text) = '{}';

But don't forget, the above query might make your CPU sweat more due to the cast.

The Sherlock Holmes: Employing NOT EXISTS

An empty JSON object, like Bigfoot, leaves no footprints (keys/values) to follow:

SELECT * FROM your_table WHERE NOT EXISTS (
  SELECT 1 FROM json_each(json_column)
);

The solid approach: Distinct and group by

For aggregate queries, you can use GROUP BY and DISTINCT to handle your JSON data like a pro:

SELECT JSON_COLUMN, COUNT(*)
FROM your_table
GROUP BY JSON_COLUMN
HAVING COUNT(DISTINCT JSON_COLUMN) = 1 AND MAX(json_column::text) = '{}';

Come rain or shine, always catch up on PostgreSQL updates for fresh JSON features like piping hot bread buns.

Performance considerations

When playing with large databases, think efficiency. Save from unnecessary casts, use jsonb when possible. Consider creating indexes on JSONB columns to help the query cruise through:

CREATE INDEX idx_jsonb_column ON your_table USING GIN (json_column);

Comment: /* first rule of fight club: you do not talk about indexing */

Variations in text representation

Beware, the boogeyman of UTF-8 may throw whitespaces and formatting variations when casting JSON to text. Regularise the JSON structure before casting to avoid getting ambushed.

The consensus on jsonb

The oracle speaks—the community inclines towards jsonb because of its indexing prowess and advanced operator compatibility.

Unraveling JSON

Counting json object pairs

count(*) from json_each(json_column) is a trustworthy sidekick that flags empty JSON objects:

SELECT * FROM your_table WHERE (SELECT count(*) FROM json_each(json_column)) > 0;

This query counts key-value pairs and filters out the empties like a champ.

Comment: /* Move aside Sherlock Holmes, you’ve met your match */

Know your enemy: Performance pitfalls

Plain text JSON can weigh like a sumo wrestler. Filter and limit the JSON data parsed to save your CPU a workout.

The secret weapon: Indexing

Launching indexes on JSON columns will feel like turbocharging queries. But remember, they’re not a silver bullet for every query kind. Make them tailor-fit to your most common query patterns.

Comment: /* Mind it, this ain't your grandpa's SQL */

Choose your method: Querying strategy

Picking the right approach to JSON querying for your use case will make all the difference. WebMD your queries for a balanced diet of precision and speed.