JSON 配列の長さとサイズの取得

例: json_array_length

JSON エンコード形式の配列の長さを取得するには、json_array_length 関数を使用します。

WITH dataset AS (
  SELECT * FROM (VALUES
    (JSON '{"name":
            "Bob Smith",
            "org":
            "legal",
            "projects": [{"name":"project1", "completed":false}]}'),
    (JSON '{"name": "Susan Smith",
            "org": "engineering",
            "projects": [{"name":"project2", "completed":true},
                         {"name":"project3", "completed":true}]}'),
    (JSON '{"name": "Jane Smith",
             "org": "finance",
             "projects": [{"name":"project2", "completed":true}]}')
  ) AS t (users)
)
SELECT
  json_extract_scalar(users, '$.name') as name,
  json_array_length(json_extract(users, '$.projects')) as count
FROM dataset
ORDER BY count DESC

このクエリは次の結果を返します。

+---------------------+
| name        | count |
+---------------------+
| Susan Smith | 2     |
+---------------------+
| Bob Smith   | 1     |
+---------------------+
| Jane Smith  | 1     |
+---------------------+

例: json_size

JSON エンコード形式の配列やオブジェクトのサイズを取得するには、json_size 関数を使用し、JSON 文字列を含む列とその配列やオブジェクトへの JSONPath 式を指定します。

WITH dataset AS (
  SELECT * FROM (VALUES
    (JSON '{"name": "Bob Smith", "org": "legal", "projects": [{"name":"project1", "completed":false}]}'),
    (JSON '{"name": "Susan Smith", "org": "engineering", "projects": [{"name":"project2", "completed":true},{"name":"project3", "completed":true}]}'),
    (JSON '{"name": "Jane Smith", "org": "finance", "projects": [{"name":"project2", "completed":true}]}')
  ) AS t (users)
)
SELECT
  json_extract_scalar(users, '$.name') as name,
  json_size(users, '$.projects') as count
FROM dataset
ORDER BY count DESC

このクエリは次の結果を返します。

+---------------------+
| name        | count |
+---------------------+
| Susan Smith | 2     |
+---------------------+
| Bob Smith   | 1     |
+---------------------+
| Jane Smith  | 1     |
+---------------------+