Bigquery: "table_a" объединяет все "table_b" и левое соединение "table_b" с таблицей "mappingstation"

Question

Я впервые работаю с sql / bigquery. Я не могу объяснить проблему ясно, потому что я не понимаю логи c из sql.

У меня есть «table_a», который я хотел бы объединить с «table_b», а затем запросить «TransactionType», « BusinessDay "и" ExitStationID ". Однако в 'table_b' "ExitStationID" - это "SiteID", который мне нужен для соединения влево с таблицей "MP_001_Station".

Я могу запросить обе таблицы. Однако ExitStationID, принадлежащий table_b, не преобразуется в правильное значение.

Вот код:

WITH bss AS (
  SELECT
    TransactionType,
    BusinessDay,
    ExitStationID
  FROM
    `table_a`
  WHERE
  EntryStationID IS NOT NULL AND ExitStationID IS NOT NULL AND
  CAST(EntryStationID as INT64) < 100 AND CAST(ExitStationID AS INT64) < 100 AND
  BusinessDay BETWEEN '2017-05-01' AND '2017-12-31'

  UNION ALL
  SELECT
    CAST(MessageTypeValue AS STRING) AS TransactionType,
    BusinessDay,
    SiteID AS ExitStationID
  FROM
    `table_b`
  WHERE
  MessageTypeValue = 20 AND BusinessDay BETWEEN '2017-05-01' AND '2017-12-31'
),

dimdate AS (
  SELECT
    EnglishDayNameOfWeek AS Day,
    DayType,
    FullDateAlternateKey
  FROM
    `DimDate`
),

dimstation AS (
  SELECT
    LineCode AS ExitLine,
    StationKey
  FROM
    `DimStation`
),

mappingstation AS (
  SELECT
    StationCodeBLU
  FROM 
    `MP_001_Station`
),

legacy AS (
  SELECT
    SiteID
  FROM `table_b`
)

SELECT 
  EXTRACT(DAYOFYEAR FROM BusinessDay) AS DayOfYear,
  EXTRACT(DATE FROM BusinessDay) AS Date,
  EXTRACT(MONTH FROM BusinessDay) AS Month,
  Day,
  DayType,
  ExitStationID,
  COUNT(*) AS Ridership

FROM bss
LEFT JOIN dimdate
ON (
  CAST(bss.BusinessDay AS date) = dimdate.FullDateAlternateKey
)

LEFT JOIN dimstation
ON (
  CAST(bss.ExitStationID AS INT64) = CAST(dimstation.StationKey AS INT64)
)

LEFT JOIN mappingstation
ON (
  CAST(bss.ExitStationID AS INT64) = CAST(mappingstation.StationCodeBLU AS INT64)
)

GROUP BY
  DayOfYear,
  Date,
  Month,
  Day,
  DayType,
  ExitStationID

ORDER BY
  DayOfYear,
  ExitStationID