MySQL 8.0

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CREATE PROCEDURE test (IN in_parameter JSON)
BEGIN
DECLARE p_array_only BOOL
    DEFAULT IFNULL(0 + JSON_EXTRACT(in_parameter, '$.array_only'), FALSE);
SELECT p_array_only;
END
CALL test ('{"array_only":true}')

p_array_only

1

CALL test ('{"array_only":false}')

p_array_only

0

CALL test ('{"array_only":1}')

p_array_only

1

CALL test ('{"array_only":0}')

p_array_only

0

CALL test ('{"array_only":5}')

p_array_only

5

CALL test ('{"array_only":null}')
Invalid JSON value for CAST to DOUBLE from column json_extract at row 1

CALL test ('{"array_only":"true"}')
Invalid JSON value for CAST to DOUBLE from column json_extract at row 1

CALL test ('{"value_only":true}')

p_array_only

0