Multi-Valued Indexes are going to change the way you think about using JSON data and the way you architect your data. Before MySQL 8.0.17 you could store data in JSON arrays but trying to search on that data in those embedded arrays was tricky and usually required a full table scan.  But now it is easy and very quick to search and to access the data in JSON arrays.
Multi-Valued IndexesA Multi-Valued Index (MVI) is a secondary index defined on a column made up of an array of values.  We are all used to traditional indexes where you have one value per index entry, a 1:1 ratio.  A MVI can have multiple records for each index record.  So you can have multiple postal codes, phone numbers, or other attributes from one JSON document indexed for quick access. See Multi-Valued Indexes for details.

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MySQL 8.0.17 adds three new functions to the JSON repertoire.  All three can take advantage of the new Multi-Value Index feature or can be used on JSON arrays.

JSON_CONTAINS(target, candiate[, path])
This function indicates with a 1 or 0 if a  candidate document is contained in the target document. The optional path argument lets you seek information in embedded documents.  And please note the 'haystack' is before the 'needle' for this function.

mysql> SELECT JSON_CONTAINS('{"Moe": 1, "Larry": 2}','{"Moe": 1}');
+------------------------------------------------------+
| JSON_CONTAINS('{"Moe": 1, "Larry": 2}','{"Moe": 1}') |
+------------------------------------------------------+
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