Can you index a nested JSON field in MySQL for better performance?

Yes, MySQL allows indexing nested JSON fields using virtual generated columns or multi-valued indexes. Create a virtual column extracting the nested value: ALTER TABLE t ADD COLUMN nested_val VARCHAR(100) AS (json_col->>'$.user.email'); then create index on that column: CREATE INDEX idx ON t(nested_val). This approach works for any nested path. MySQL 8.0.17+ supports functional indexes directly on JSON expressions: CREATE INDEX idx ON t((json_col->>'$.user.email')). Multi-valued indexes handle array elements: CREATE INDEX idx ON t((CAST(json_col->'$.tags' AS CHAR(50) ARRAY))). Generated columns add storage overhead but enable fast lookups. Indexes make nested JSON queries perform comparably to regular column indexes. Without indexes, queries scan entire tables checking each JSON document. Use EXPLAIN to verify index usage in queries. Test JSON structure with our JSON Viewer at jsonconsole.com/json-viewer to identify frequently queried paths for indexing. Index only paths you actually query to avoid unnecessary overhead. Proper indexing transforms slow JSON queries into fast operations matching relational performance.