Pivot sql output - Google sql 面试问题

Question

I have asked to query a table to return the names of the student that starts with A along with their count. Let us table has "Alan" and "Adam" entry. The output should be 2, Alan, Adam.

Answer 1

You can use left() , and string_agg() .

Option 1: which you have asked for.

select
    count(firstChar) as totalCount,
    string_agg(fname, ', ') as allNames
from
(
    select 
        fname,
        left(fname, 1) as firstChar
    from myName
) res
group by
   firstChar

Output: DEMO

*----------------------*
|totalcount | allnames |
*----------------------*
|   2       |Adam, Alan|
*----------------------*

Option 2:

select 
    left(fname, 1) as firstChar, 
    count(left(fname, 1)) as total
from myName
group by
    left(fname, 1)

Output: DEMO

*-------------------*
|firstChar  | count |
*-------------------*
|   A       |    2  |
*-------------------*

Answer 2

You can use left() with window function:

select name, count(*) over ()
from table t
where left(fname, 1) = 'a';

Edit: Use string_agg() to concat strings into single row:

select count(*), string_agg(fname, ', ')
from table t
where left(fname, 1) = 'a';

Answer 3

In BigQuery, I would use array_agg() :

select count(*), array_agg(name)
from t
where name like 'A%';

Answer 4

Please find Answer as per your output: I have created a table below:

Create table dbo.test_table (FNAME varchar(50));

insert into dbo.test_table(FNAME) values
('Alan'),
('Adam')
         

Query for the output:

with CTE AS (
SELECT
    COUNT(*) as total_Count,
    string_agg(fname, ', ') as First_Names
FROM dbo.test_table
WHERE LEFT(FNAME,1)='A'
  )
  SELECT CONCAT(total_Count,',', First_Names) As output FROM CTE

SQL Fiddle Link for output: SQLFiddle