sql 查询嵌套数组

查询嵌套数组
如果一个表包含 STRUCT 的 ARRAY，则可展平 ARRAY 以查询 STRUCT 的字段。您也可以展平 STRUCT 值的 ARRAY 类型字段。

查询 ARRAY 中的 STRUCT 元素
以下示例将 UNNEST 与 CROSS JOIN 结合使用，以展平 STRUCT 的 ARRAY。

WITH races AS (
  SELECT "800M" AS race,
    [STRUCT("Rudisha" as name, [23.4, 26.3, 26.4, 26.1] as splits),
     STRUCT("Makhloufi" as name, [24.5, 25.4, 26.6, 26.1] as splits),
     STRUCT("Murphy" as name, [23.9, 26.0, 27.0, 26.0] as splits),
     STRUCT("Bosse" as name, [23.6, 26.2, 26.5, 27.1] as splits),
     STRUCT("Rotich" as name, [24.7, 25.6, 26.9, 26.4] as splits),
     STRUCT("Lewandowski" as name, [25.0, 25.7, 26.3, 27.2] as splits),
     STRUCT("Kipketer" as name, [23.2, 26.1, 27.3, 29.4] as splits),
     STRUCT("Berian" as name, [23.7, 26.1, 27.0, 29.3] as splits)]
       AS participants)
SELECT
  race,
  participant
FROM races r
CROSS JOIN UNNEST(r.participants) as participant;

+------+---------------------------------------+
| race | participant                           |
+------+---------------------------------------+
| 800M | {Rudisha, [23.4, 26.3, 26.4, 26.1]}   |
| 800M | {Makhloufi, [24.5, 25.4, 26.6, 26.1]} |
| 800M | {Murphy, [23.9, 26, 27, 26]}          |
| 800M | {Bosse, [23.6, 26.2, 26.5, 27.1]}     |
| 800M | {Rotich, [24.7, 25.6, 26.9, 26.4]}    |
| 800M | {Lewandowski, [25, 25.7, 26.3, 27.2]} |
| 800M | {Kipketer, [23.2, 26.1, 27.3, 29.4]}  |
| 800M | {Berian, [23.7, 26.1, 27, 29.3]}      |
+------+---------------------------------------+

查询 STRUCT 中的 ARRAY 类型字段
您也可以从嵌套的重复字段中获取信息。例如，以下语句用于返回在 800 米赛跑中圈速最快的参赛选手。

WITH races AS (
 SELECT "800M" AS race,
   [STRUCT("Rudisha" as name, [23.4, 26.3, 26.4, 26.1] as splits),
    STRUCT("Makhloufi" as name, [24.5, 25.4, 26.6, 26.1] as splits),
    STRUCT("Murphy" as name, [23.9, 26.0, 27.0, 26.0] as splits),
    STRUCT("Bosse" as name, [23.6, 26.2, 26.5, 27.1] as splits),
    STRUCT("Rotich" as name, [24.7, 25.6, 26.9, 26.4] as splits),
    STRUCT("Lewandowski" as name, [25.0, 25.7, 26.3, 27.2] as splits),
    STRUCT("Kipketer" as name, [23.2, 26.1, 27.3, 29.4] as splits),
    STRUCT("Berian" as name, [23.7, 26.1, 27.0, 29.3] as splits)]
    AS participants)
SELECT
race,
(SELECT name
 FROM UNNEST(participants),
   UNNEST(splits) AS duration
 ORDER BY duration ASC LIMIT 1) AS runner_with_fastest_lap
FROM races;

+------+-------------------------+
| race | runner_with_fastest_lap |
+------+-------------------------+
| 800M | Kipketer                |
+------+-------------------------+