How can we change the datatype of a column using standard SQL in bigquery?

Question

I know this may be stupid but none of the old cases works for me. And neither for 'CAST' method as well.

I'm trying to run the following query and I got the following error:

SELECT
  P.date,
  P.campaign_id,
  P.ad_name,
  P.impressions,
  P.clicks,
  P.spend,
  P.NOM_ENSEMBLE,
  P.CODE_ENSEMBLE_IMMO,
  F.FREQUENTATION_CENTRE
FROM
  `project.digital.fb_data` AS P
JOIN
  `project.digital.freq_data` AS F
ON
  (P.date = F.JOUR AND P.CODE_ENSEMBLE_IMMO=F.CODE_ENSEMBLE_IMMO)

Error:

Error: No matching signature for operator = for argument types: DATE, STRING. Supported signatures: ANY = ANY at [16:4]

Answer 1

Below is for BigQuery Standard SQL

First query is simplified query that reproduces / demonstrates your issue

#standardSQL
WITH `project.digital.fb_data` AS (
  SELECT DATE '2019-02-15' `date`, 1 CODE_ENSEMBLE_IMMO 
),  `project.digital.freq_data` AS (
  SELECT '02-15-2019' JOUR, 1 CODE_ENSEMBLE_IMMO, 'zzz' FREQUENTATION_CENTRE
)
SELECT
  P.date,
  P.CODE_ENSEMBLE_IMMO,
  F.FREQUENTATION_CENTRE
FROM `project.digital.fb_data` AS P
JOIN `project.digital.freq_data` AS F
ON P.date = F.JOUR 
AND P.CODE_ENSEMBLE_IMMO=F.CODE_ENSEMBLE_IMMO   

with result

Error: No matching signature for operator = for argument types: DATE, STRING. Supported signatures: ANY = ANY at [13:4]  

Below query demonstrates how to resolve above issue

#standardSQL
WITH `project.digital.fb_data` AS (
  SELECT DATE '2019-02-15' `date`, 1 CODE_ENSEMBLE_IMMO 
),  `project.digital.freq_data` AS (
  SELECT '02-15-2019' JOUR, 1 CODE_ENSEMBLE_IMMO, 'zzz' FREQUENTATION_CENTRE
)
SELECT
  P.date,
  P.CODE_ENSEMBLE_IMMO,
  F.FREQUENTATION_CENTRE
FROM `project.digital.fb_data` AS P
JOIN `project.digital.freq_data` AS F
ON P.date = PARSE_DATE('%m-%d-%Y', F.JOUR)
AND P.CODE_ENSEMBLE_IMMO=F.CODE_ENSEMBLE_IMMO   

with result

Row date        CODE_ENSEMBLE_IMMO  FREQUENTATION_CENTRE     
1   2019-02-15  1                   zzz       

Note: you can have your F.JOUR un a different format than in above example - so check PARSE_DATE function for how to deal with other supported formats