equating an entry to an aggregated version of itself - google-bigquery

Question

I am trying to find if an entry's value is the max of the grouped value. Its purpose is to sit in a larger if logic.
Which I'd expect would look something like this:
SELECT
t.id as t_id,
sum(if(t.value = max(t.value), 1, 0)) AS is_max_value
FROM dataset.table AS t
GROUP BY t_id
The response is:
Error: Expression 't.value' is not present in the GROUP BY list
How should my code look to do this?

Answer 1

You first need to compile in a subquery the max value, then join again the value to the table.
Using the public data set available here is an example:
SELECT
t.word,
t.word_count,
t.corpus_date
FROM
[publicdata:samples.shakespeare] t
JOIN (
SELECT
corpus_date,
MAX(word_count) word_count,
FROM
[publicdata:samples.shakespeare]
GROUP BY
1 ) d
ON
d.corpus_date=t.corpus_date
AND t.word_count=d.word_count
LIMIT
25
Results:
+-----+--------+--------------+---------------+---+
| Row | t_word | t_word_count | t_corpus_date | |
+-----+--------+--------------+---------------+---+
| 1 | the | 762 | 1597 | |
| 2 | the | 894 | 1598 | |
| 3 | the | 841 | 1590 | |
| 4 | the | 680 | 1606 | |
| 5 | the | 942 | 1607 | |
| 6 | the | 779 | 1609 | |
| 7 | the | 995 | 1600 | |
| 8 | the | 937 | 1599 | |
| 9 | the | 738 | 1612 | |
| 10 | the | 612 | 1595 | |
| 11 | the | 848 | 1592 | |
| 12 | the | 753 | 1594 | |
| 13 | the | 740 | 1596 | |
| 14 | I | 828 | 1603 | |
| 15 | the | 525 | 1608 | |
| 16 | the | 363 | 0 | |
| 17 | I | 629 | 1593 | |
| 18 | I | 447 | 1611 | |
| 19 | the | 715 | 1602 | |
| 20 | the | 717 | 1610 | |
+-----+--------+--------------+---------------+---+
You can see that retains the word that have the maximum word_count in the partition defined by corpus_date

Answer 2

Use window function to "spread" the max value over all relevant records.
this way you can avoid the Join.
SELECT
*
FROM (
SELECT
corpus,
corpus_date,
word,
word_count,
MAX(word_count) OVER (PARTITION BY corpus) AS Max_Word_Count
FROM
[publicdata:samples.shakespeare] )
WHERE
word_count=Max_Word_Count

Answer 3

select
id,
value,
integer(value = max_value) as is_max_value
from (
select id, value, max(value) over(partition by id) as max_value
from dataset.table
)
Explanation:
Inner select - for each row/record calculates max of value among all rows with the same id
Outer select - for each row/record compares row's value with max value for respective group and then converts true or false into respectively 1 or 0 (as per expectation in question)