If you’re getting an error that reads “function array_sample(integer, integer) does not exist” when using the array_sample() function in PostgreSQL, it’s probably because your first argument is not an array. In particular, this specific error message implies that the first argument is an integer.
The first argument for this function must be an array.
To fix this error, be sure that your first argument to array_sample() is an array, not an integer.
In PostgreSQL array_sample() is a system function that returns an array of a specified number of items randomly selected from the given array.
The array_sample() function was introduced in PostgreSQL 16, which was released on September 14th 2023.
In SQL Server, we can use the JSON_ARRAY() function to construct JSON array text from zero or more expressions.
The resulting array contains the values we provide as arguments. Providing zero expressions results in an empty array.
In MySQL, the MEMBER OF() operator tests whether or not a value is a member of a given JSON array.
It returns true (1) if the array contains the value, and false (0) if it doesn’t.
The MEMBER OF() operator was added in MySQL 8.0.17.
In Redis, the SMEMBERS command returns all members of a given set. We specify the key name of the set when we call the command.
In Redis, we can use the SMISMEMBER command to find out whether one or more members are in a given set. It’s similar to the SISMEMBER command, except that it allows us to check more than one member at a time.
The SMISMEMBER command was introduced in Redis 6.2.0.
In SQLite, the json_array_length() function returns the number of elements in a given JSON array.
The array is provided as an argument. If the array is embedded within a larger JSON document, we can use an optional second argument to specify the path to the array.
If the value is not an array, the function returns 0.
The SQLite json_group_array() function is an aggregate function that returns a JSON array comprised of all values in the aggregation.
In other words, it constructs an array from the values provided by its argument.
In SQLite, the json_array() function returns a well-formed JSON array based on its arguments.
The function accepts zero or more arguments, and each argument becomes an element in the resulting array.
MariaDB includes two selectors that enable us to select elements from JSON arrays:
[N] selects element number N in the array (for example, [0] to select the first element). [*] selects all elements in the array.These can be used in a number of JSON functions that are included in MariaDB. The following examples use them with the JSON_EXTRACT() function in order to return selected array elements.