MySQL 8.0.17 has the ability to create indexes over JSON arrays to speed up your queries. This presentation shows examples and explain all you need to know about this new feature: How are array indexes created? How do they work? When are they used? Are there any limitations?

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JSON array indexes
in MySQL
Norvald H. Ryeng
Software Development Senior Manager
MySQL Optimizer Team
October 2, 2019
New in
8.0.17

2. Copyright © 2019 Oracle and/or its affiliates.2
Safe harbor statement
The following is intended to outline our general product direction. It is intended for information
purposes only, and may not be incorporated into any contract. It is not a commitment to deliver
any material, code, or functionality, and should not be relied upon in making purchasing
decisions.
The development, release, timing, and pricing of any features or functionality described for
Oracle’s products may change and remains at the sole discretion of Oracle Corporation.

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Program agenda
1 What is it?
2 How do I use it?
3 Demo

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What is it?
 Index of a JSON array
A functional index over a JSON expression
The expression evaluates to an array
 Several index entries per row
One index entry per array element
General mechanism, currently used for JSON arrays
 Used to speed up array lookups
JSON_CONTAINS(…)
JSON_OVERLAPS(…)
MEMBER OF (…)

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Limitations
 Can be part of a multi-column index
Only one array expression per index
Avoiding combinatorial explosion
 Can flatten and index nested arrays
CAST(json->'$.the_array[*][*]' AS UNSIGNED INT ARRAY)
 Can't be PRIMARY
 Can be UNIQUE

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How do I use it?
CREATE TABLE lottery (data JSON);
CREATE INDEX ticket_idx ON lottery ((CAST(data->'$.lottery_tickets' AS UNSIGNED INT ARRAY)));
INSERT INTO lottery VALUES
('{"id":1, "name":"Alice", "lottery_tickets": [1]}'),
('{"id":2, "name":"Bob", "lottery_tickets": [2,22]}'),
('{"id":3, "name":"Carol", "lottery_tickets": [3,33,333]}'),
('{"id":4, "name":"Dan", "lottery_tickets": [4,44,444,4444]}'),
('{"id":5, "name":"Erin", "lottery_tickets": [5,55,555,5555,55555]}');
Cast to array is only available
when creating a functional index
Type of array element

7. Copyright © 2019 Oracle and/or its affiliates.7
New in
8.0.17
How do I use it?
Find all rows where the array contains a given value
SELECT data
FROM lottery
WHERE JSON_CONTAINS(data->'$.lottery_tickets', CAST(22 AS JSON));
or
SELECT data FROM lottery WHERE 22 MEMBER OF (data->'$.lottery_tickets');
Find the one winner

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How do I use it?
Find all rows that contain one or more of the given values
SELECT data
FROM lottery
WHERE JSON_OVERLAPS(data->'$.lottery_tickets', CAST('[22,44]' AS JSON));
Find everyone with at
least one winning ticket
New in
8.0.17

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Demo
MySQL 8.0.17

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Feature descriptions and design details
directly from the source
https://mysqlserverteam.com/

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Thank you!
Norvald H. Ryeng
Software Development Senior Manager
MySQL Optimizer Team