What is the method to distinguish the presence of a json field in an array using presto?

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The method to distinguish the presence of a JSON field in an array using Presto is to use the "json_extract" function. This function can extract the value of a JSON field from a given JSON object or array.

To determine the presence of a JSON field in an array, you can use the "jsonextractscalar" function with the "cardinality" function. The "jsonextractscalar" function is used to extract the scalar value of a JSON field, and the "cardinality" function is used to determine the number of elements in the result set. If the result set has a cardinality greater than zero, it means that the JSON field is present in the array.

For example, to determine if a JSON field called "color" is present in an array called "my_array", you can use the following query:

SELECT cardinality(jsonextractscalar(myarray, '$[*].color')) > 0 AS iscolorpresent FROM mytable

In this query, the "jsonextractscalar" function is used to extract the value of the "color" field from all elements in the "my_array" array. The "cardinality" function is used to determine the number of elements in the result set, which indicates the presence or absence of the "color" field in the array. The result set of this query will be a boolean value indicating whether the "color" field is present in the array.