SQL Count 在 GBQ 表中的不同行数

Question

I'd like to count the number of distinct rows in a table. I know that I can do that using groupby or by naming all the columns one by one, but would like to just do:

select count(distinct *) from my_table

Is that possible?

Answer 1

Do SELECT DISTINCT in a derived table (the subquery), then count the number of rows returned.

select count(*) from
(select distinct * from my_table) dt

(Doesn't your table have any primary key?)

Answer 2

You can use to_json_string() :

select count(distinct to_json_string(t))
from t;

Answer 3

Below more options for BigQuery Standard SQL

select count(distinct format('%t', t))
from `project.dataset.table` t

depends on your use case - approximate count can be even more optimal option

select approx_count_distinct(format('%t', t))
from `project.dataset.table` t

APPROX_COUNT_DISTINCT - returns the approximate result for COUNT(DISTINCT expression). The value returned is a statistical estimate—not necessarily the actual value. This function is less accurate than COUNT(DISTINCT expression), but performs better on huge input .

Answer 4

The use of count(distinct *) is not permitted.

Alternatively you could explicitly name the columns (what defines uniqueness).