BigQuery: Lookup array of ids type RECORD and join data from secondary table using SQL

问题

I have a data structure like below:

Products

| name  | region_ids             |
----------------------------------
| shoe  | c32, a43, x53          |
| hat   | c32, f42               |

# Schema
name                STRING  NULLABLE
region_ids          RECORD  REPEATED    
region_ids.value    STRING  NULLABLE

Regions

| _id |  name       |
---------------------
| c32 |  london     |
| a43 |  manchester |
| x53 |  bristol    |
| f42 |  liverpool  |

# Schema
_id                 STRING  NULLABLE
name                STRING  NULLABLE

I want to look up the array of "region_ids" and replace them by the region name to result in a table like below:

| _id |  name  | region_names                |
----------------------------------------------
| d22 |  shoe  | london, manchester, bristol |
| t64 |  hat   | london, liverpool           |

What is the best way to do this using standard SQL?

Thanks,

回答1:

Below is for BigQuery Standard SQL

#standardSQL
SELECT p._id, p.name, 
  STRING_AGG(r.name, ', ' ORDER BY OFFSET) AS region_names 
FROM `project.dataset.Products` p,
UNNEST(region_ids) WITH OFFSET
LEFT JOIN `project.dataset.Regions` r
ON value = r._id
GROUP BY _id, name

You can test, play with above using sample data from your question as in below example

#standardSQL
WITH `project.dataset.Products` AS (
  SELECT 'd22' _id, 'shoe' name, [STRUCT<value STRING>('c32'), STRUCT('a43'), STRUCT('x53')] region_ids UNION ALL
  SELECT 't64', 'hat', [STRUCT<value STRING>('c32'), STRUCT('f42')]
), `project.dataset.Regions` AS (
  SELECT 'c32' _id, 'london' name UNION ALL
  SELECT 'a43', 'manchester' UNION ALL
  SELECT 'x53', 'bristol' UNION ALL
  SELECT 'f42', 'liverpool' 
)
SELECT p._id, p.name, 
  STRING_AGG(r.name, ', ' ORDER BY OFFSET) AS region_names 
FROM `project.dataset.Products` p,
UNNEST(region_ids) WITH OFFSET
LEFT JOIN `project.dataset.Regions` r
ON value = r._id
GROUP BY _id, name

Result is

Row _id name    region_names     
1   d22 shoe    london, manchester, bristol  
2   t64 hat     london, liverpool

Based on output example in your question - you expect region_names as string with list of comma separated names
But, if you need region_names as an array - you can replace STRING_AGG(r.name, ', ' ORDER BY OFFSET) with ARRAY_AGG(r.name ORDER BY OFFSET)

来源：https://stackoverflow.com/questions/62808554/bigquery-lookup-array-of-ids-type-record-and-join-data-from-secondary-table-usi

标签

mysql

join

google-bigquery

record