![]() It can only appear at the start of the path expression $ (dollar sign) is a special identifier, which is essentially a placeholder for the current document being operated on. ![]() There are 4 types of identifiers that can appear in a path: While the path is passed as a string value, it's actually an expression consisting of alternating identifiers and access operators that as a whole identifies a particular piece within the JSON document: Identifiers The modified document is always returned from the function as a new document. It is important to point out that none of the functions that modify JSON documents actually change the argument document inline: JSON functions are pure functions that don't have side effects. Depending on which function exactly, other arguments may or may not accept path expressions as well. In general, the second argument of functions that manipulate JSON documents is a path expression. The path is an expression that identifies which part of the document to operate on. In general, functions that manipulate JSON documents accept the document that is being operated on as their first argument. This can be an explicit or implicitly obtained JSON document, constructed in any of the ways described earlier in this post. Manipulation of JSON documents always involves at least two distinct items: While the JSON document may be a convenient unit for storing and transporting related items of data, any meaningful processing of such documents will always involve some operation to transform or modify such a document: for example, extracting some item stored inside the document, or adding or removing properties or array elements. ![]() Operating on JSON documents: Extraction and Modification In these cases, the return value represents a modified instance of the document passed as argument. Unlike JSON_QUOTE(), JSON_ARRAY() and JSON_OBJECT(), most of these also require a JSON document as their first argument. There are many more built-in JSON functions that return a value of the JSON data type. However, as we shall see later on, this approach is not entirely equivalent to constructing these documents through JSON_ARRAY and JSON_OBJECT. | object | array | null | true | false | string | If the value you're casting is of a character string type, then its value should be parseable as either a JSON object or a JSON array (i.e., JSON documents), as a JSON keyword indicating a built-in value, like null, true, false, or as a properly quoted JSON string value: | CAST(1 AS JSON) | CAST(1.1 AS JSON) | CAST(NOW() AS JSON) |Įven though it may not be immediately clear from the result, the CAST operation actually turned these values into JSON equivalents. Mysql> SELECT CAST(1 AS JSON), CAST(1.1 AS JSON), CAST(NOW() AS JSON) AS JSON) CAST a value of any non-character string type AS JSON to obtain a JSON representation of that value. There are a number of ways to create values of the JSON type: Rather, I will highlight a few things I observed and I hope that this will be helpful for others that want to get started with JSON in MySQL 5.7. There is potentially a lot to write and explain about the JSON support, and I can't hope to completely cover the subject in one blog post. (We can of course also phrase this more pessimistically and say that XML support falls short on these accounts, but that's not what this post is about :-) ![]() Improvements are certainly possible, but compared to for example XML support (added in 5.1 and 5.5), the JSON feature set added to 5.7.8 is reasonably complete, coherent and standards-compliant.
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