SQL for JSON Rationalization Part 9: Restriction – Arrays

This installment reviews restriction in JSON SQL based on JSON array literals (all other JSON types except JSON array have been discussed in previous blogs).

JSON Object Notation

JSON SQL follows the JSON object notation as defined in the JSON standard. An empty JSON array is denoted as [] and a non-empty JSON array has one or more comma separated values, including JSON array.

A JSON array literal is either an empty JSON array or a non-empty JSON array. A JSON array literal is not enclosed in quotes. The only JSON literal enclosed in quotes is JSON string. If a JSON array is enclosed in quotes then it is not a JSON array, but a JSON string.

Sample Document Set

The following document set is used in this blog and the documents are stored in a collection called “arrayColl”.

select {*} from arrayColl

results in

{"one":[{"a":1},{"b":2}]}
{"one":"[{\"a\": 1}, {\"b\": 2}]"}
{"three":[{"b":[{"c":null},{"d":true}]}]}
{"four":[{"x":8,"y":9}]}
{"five":[]}

Restriction based on JSON Object Literal

Starting with the empty JSON array literal, the following two queries product the same result.

select {*} from arrayColl where five = []

and

select {*} from arrayColl where [] = five

result in

{"five":[]}

In the following, queries show the JSON array literal on the right side of the operator, however, it can be on either side.

Operators = And <>

The operators = and <> are defined for a JSON array literal. JSON SQL regards two JSON arrays as equal if both have the same (equal) values in the same order; and not equal otherwise.

The query (restriction using JSON array literal)

select {*} from arrayColl where one = [{"a": 1}, {"b": 2}]

returns

{"one":[{"a":1},{"b":2}]}

The query (restriction using JSON string literal(!))

select {*} from arrayColl where one = '[{"a": 1}, {"b": 2}]'

returns

{"one":"[{\"a\": 1}, {\"b\": 2}]"}

A restriction can reach into the JSON array as well using the path notation. The query

select {*}
from arrayColl
where three.[0].b = [{"c": null}, {"d": true}]

returns

{"three":[{"b":[{"c":null},{"d":true}]}]}

Operators <, >, <= And >=

The operators <, >, <= and >= could be defined recursively for convenience with some restrictions. For example, a JSON array could be considered less than another JSON array if both have the same values and if the corresponding values are less than another.

However, JSON true, JSON false and JSON null would not be able to participate in the operator <, >, <= or >=, only JSON object, JSON array, JSON number and JSON string.

Those four operators are currently not directly implemented in JSON SQL since it is possible to achieve the same by writing a complex conjunctive restriction (details on this approach will be discussed in a subsequent blog as well as strategies of what to do if any of JSON true, JSON false or JSON null are present).

Canonical Interpretation

The order of the values inside a JSON array is significant, but not within a JSON object. The query

select {*} from arrayColl where four = [{"y": 9, "x": 8}]

therefore results in

{"four":[{"x":8,"y":9}]}

Summary

Restriction by JSON array is provided by JSON SQL without problem and the syntax extends the Relational SQL syntax naturally.

Go [ JSON | Relational ] SQL!

Disclaimer

The views expressed on this blog are my own and do not necessarily reflect the views of Oracle.

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