JSON type in MySQL

Last reviewed May 28, 2026 Content v20260528

Track mode

sql_sandbox

Means

SQL sandbox

Reading

~1 min

Level

intermediate

This lesson

This lesson teaches JSON type in MySQL: the SQL patterns, schema habits, and query reasoning you need before advancing in MySQL.

Teams query JSON type in MySQL on every MySQL codebase—skipping it leaves gaps in debugging and data reviews.

You will apply JSON type in MySQL in contexts like: Product config and feature flags in JSON columns—know when Postgres JSONB would index better.

Copy MySQL SQL into the mysql client, local MySQL/MariaDB, or DB Fiddle (MySQL dialect)—use DESCRIBE and EXPLAIN where lessons show them. The in-browser lab ships later; mysql client is the practice path now.

When you can explain the previous lesson's ideas without copying example queries verbatim.

Native JSON column with functions JSON_EXTRACT, ->, ->> (5.7+), and generated columns for indexing.

Store and query

CREATE TABLE configs (
  id INT AUTO_INCREMENT PRIMARY KEY,
  body JSON NOT NULL
);

INSERT INTO configs (body) VALUES ('{"theme":"dark","beta":true}');
SELECT id, body->>'$.theme' AS theme FROM configs WHERE body->>'$.beta' = 'true';

Practice: Run on practice.

Compare Postgres JSONB

Postgres JSONB indexing is richer—see PostgreSQL when JSON queries dominate.

Important interview questions and answers

Q: -> vs ->>?
A: -> returns JSON; ->> returns unquoted SQL string.
Q: Validate JSON?
A: Invalid JSON rejected on insert into JSON column.

Self-check

Extract theme from body JSON.
Difference -> and ->>?

Tip: Use ->> for string comparisons in WHERE.

Interview prep

->> ?: Returns unquoted scalar from JSON path.
Invalid JSON?: Insert rejected into JSON column.

Discussion

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Starter discussion topics

-> vs ->>?
Postgres JSONB?

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