BigQuery：从 SQL 中的日期（字符串类型）中提取月份

Question

I've connected my GA account to Bigquery.

Now, I'm trying to group_by month all visits.

But I'm getting:

EXTRACT does not support arguments of type: STRING at [2:3] 

Because my date column is of type STRING.

SELECT
      EXTRACT(DATE_TIME_PART FROM date) AS Month, SUM(totals.visits) as totalVisits, 
    FROM
      `xxxx.yyyy.ga_sessions_20*`
    GROUP BY date

I've tried to CAST it to date:

SELECT
  EXTRACT(DATE_TIME_PART FROM CAST(date AS date)) AS Month, SUM(totals.visits) as totalVisits, 
FROM
  `xxx-yyyy.ga_sessions_20*`
GROUP BY date 

Getting:

A valid date part name is required but found DATE_TIME_PART at [2:11] Learn More about BigQuery SQL Functions.

What does it mean?

Expected result:

| year | month    | total_visits |
|:----:|----------|--------------|
| 2019 |  january | 162626       |
| 2019 | february | 599562       |

UPDATE 1:

SELECT
 FORMAT_DATE(CAST(date AS date), '%B'), SUM(totals.visits) as totalVisits, 
FROM
  `xxx.yyyy.ga_sessions_20*`
GROUP BY date 

Gives error:

No matching signature for function FORMAT_DATE for argument types: DATE, STRING. Supported signature: FORMAT_DATE(STRING, DATE) at [2:2]

Answer 1

Below is for BigQuery Standard SQL

#standardSQL
SELECT
 FORMAT_DATE('%Y', PARSE_DATE('%Y%m%d', date)) AS year, 
 FORMAT_DATE('%B', PARSE_DATE('%Y%m%d', date)) AS month, 
 SUM(totals.visits) AS totalVisits, 
FROM 
 `xxx.yyyy.ga_sessions_20*`
GROUP BY year, month 

Answer 2

If you want a number, then the correct syntax is:

SELECT EXTRACT(MONTH FROM CAST(date AS date)) AS Month

If you want the full name, then use FORMAT() :

SELECT FORMAT_DATE(CAST(date AS date), '%B')

I would recommend that you include the year as well.