Postgres得到计数但是由另一列分组

Question

If I have a table like

customer liked
1        true
2        true
3        true
1        true
2        false

How can I count the total liked but group by customer, so I end up with something like:

customer total_likes
1        2
2        1
3        1

Answer 1

GROUP BY and a condition COUNT should do:

SELECT customer, COUNT(CASE WHEN liked = 'true' THEN 1 END) AS likes
FROM yourtable
group by customer

if it's a boolean column, do:

SELECT customer, COUNT(CASE WHEN liked THEN 1 END) AS likes
FROM yourtable
group by customer

Answer 2

In Postgres, you can use the shorthand for conversion from a boolean to an integer:

select customer, sum(liked::int) as total_likes
from t
group by customer;

Note that this will return all customers , not only those with likes. If you only want customers with likes, then a where clause is appropriate:

select customer, count(*)
from t
where liked
group by customer;

Answer 3

SELECT CUSTOMER, COUNT(LIKED) AS TOTAL_LIKES
FROM TABLE
WHERE LIKED = 'true'
GROUP BY CUSTOMER

Answer 4

I assume that liked is a boolean type field,

SELECT customer, COUNT(liked) AS total_likes
FROM table_name 
WHERE liked is true
GROUP BY customer

Answer 5

Use a CASE statement inside of a COUNT function.

SELECT customer, COUNT(CASE WHEN liked = 'true' THEN 1 ELSE NULL END) AS total_likes
FROM yourtable