The size(...) function is used to calculate the collection size for the MAP, ARRAY, or nested MAP/ARRAY. It returns -1 if the collection is NULL and returns 0 if the collection is empty, as follows:
> SELECT > SIZE(work_place) as array_size,> SIZE(skills_score) as map_size,> SIZE(depart_title) as complex_size,> SIZE(depart_title["Product"]) as nest_size> FROM employee;+-------------+-----------+---------------+------------+| array_size | map_size | complex_size | nest_size |+-------------+-----------+---------------+------------+| 2 | 1 | 1 | 2 || 1 | 1 | 2 | 1 || 1 | 1 | 2 | -1 || 1 | 2 | 1 | -1 |+-------------+-----------+---------------+------------+4 rows selected (0.062 seconds)> SELECT size(null), size(array(null)), ...
