如何计算联接表的每一行中值的出现次数？

Question

I am creating a database for a hotel system using sql developer and oracle 11g and I need to print the first_name, last_name, email and how many times each person (email) visited the hotel. I therefore need to count how many times email occurs in the booking table.

I have 2 tables to join:

• Customer:

first_name last_name phone address town email postcode

• Booking:

Date_ room occupants arrival_time nights paid email_

I wish to display first_name, last_name, email, COUNT(email)

How can I do this?

Answer 1

SELECT   first_name, last_name, customer.email, visits
FROM     customer
JOIN     (SELECT   email_, COUNT(*) AS visits
          FROM     bookings
          GROUP BY email_) v
ON       customer.email = v.email_

Answer 2

It will be one to many relation:

SELECT  c.first_name, c.last_name, c.email, COUNT(c.email)
FROM    customer  c
JOIN    booking  b
ON      c.email = b.email_
GROUP   BY
        c.first_name, c.last_name, c.email
;

The same as:

SELECT  x.col, count(x.col)
FROM
(
        SELECT 1 col FROM DUAL UNION ALL
        SELECT 2     FROM DUAL
) x
JOIN
(
        SELECT 1 col FROM DUAL UNION ALL
        SELECT 1     FROM DUAL UNION ALL
        SELECT 2     FROM DUAL UNION ALL
        SELECT 2     FROM DUAL UNION ALL
        SELECT 2     FROM DUAL UNION ALL
        SELECT 3     FROM DUAL
)  y
ON      x.col = y.col
GROUP   BY
        x.col
;
/*
1   2
2   3
*/