我正在尝试在SQL中创建一个计算列。基本上我需要获得一组不同的日期，并确定该特定日期的人口中有多少客户。结果应该是这样的：
日期______ |客户
2016-01-01 | 1
2016-01-01 | 2
2016-01-05 | 3
2016-02-09 | 4
等
我创建了一个示例数据库＆amp;数据（使用MySQL，因为我没有权限在我们的Oracle dbs中创建表），使用以下脚本：
create database customer_example;
use customer_example;
create table customers (
customer_id int not null primary key,
customer_name varchar(255) not null,
term_date DATE);
create table employee (
employee_id int not null primary key,
employee_name varchar(255) not null);
create table cust_emp (
ce_id int not null AUTO_INCREMENT,
emp_id int not null,
cust_id int not null,
start_date date,
end_date date,
deleted_yn boolean,
primary key (emp_id, cust_id, ce_id),
foreign key (cust_id) references customers(customer_id),
foreign key (emp_id) references employee(employee_id));
insert into customers (customer_id, customer_name)
values (1, 'Bobby Tables'), (2, 'Grover Cleveland'), (3, 'Chester Arthur'), (4, 'Jan Bush'), (5, 'Emanuel Porter'), (6, 'Darren King'), (7, 'Casey Mcguire'), (8, 'Robin Simpson'), (9, 'Robin Tables'), (10, 'Mitchell Arnold');
insert into customers (customer_id, customer_name, term_date)
values (11, 'Terrell Graves', '2017-01-01'), (12, 'Richard Wagner', '2016-10-31'), (13, 'Glenn Saunders', '2016-11-19'), (14, 'Bruce Irvin', '2016-03-11'), (15, 'Glenn Perry','2016-06-06'), (16, 'Hazel Freeman', '2016-07-10'),
(17, 'Martin Freeman', '2016-02-11'), (18, 'Morgan Freeman', '2017-02-01'), (19, 'Dirk Drake', '2017-01-12'), (20, 'Fraud Fraud', '2016-12-31');
insert into employee (employee_id, employee_name)
values (1000, 'Cedrick French'), (1001, 'Jane Phillips'), (1002, 'Brian Green'), (1003, 'Shawn Brooks'), (1004, 'Clarence Thomas');
insert into cust_emp (emp_id, cust_id, start_date, end_date)
values (1000, 1, '2016-01-01', '2016-02-01'), (1000, 1, '2016-02-01', '2016-02-01'), (1000, 2,'2016-01-05', '2016-01-16'),(1000, 3,'2016-02-09', '2016-03-14'),(1000, 4,'2016-03-20', '2016-04-23'),
(1000, 5,'2016-01-01', '2016-01-16'),(1000, 6,'2016-01-01', '2016-01-16'),(1004, 7, '2016-01-14', '206-01-16'),
(1004, 8, '2016-01-13', '2016-01-16'),(1004, 9, '2016-01-05', '2016-01-16'), (1003, 12, '2016-04-21', '2016-11-30');
insert into cust_emp (emp_id, cust_id, start_date, deleted_yn)
values (1002, 11, '2016-04-10', TRUE),(1003, 10, '2016-01-16', FALSE), (1004, 12, '2016-04-20', TRUE), (1004, 12, '2016-04-19', FALSE), (1003, 13, '2016-06-06', TRUE), (1002, 14, '2016-06-10', TRUE),
(1004, 15, '2016-03-25', TRUE), (1004, 17, '2016-01-02', TRUE), (1004, 18, '2017-01-01', TRUE), (1004, 19, '2016-11-13', TRUE), (1004, 20, '2016-03-10', TRUE), (1004, 16, '2016-05-13', TRUE);
insert into cust_emp (emp_id, cust_id, start_date)
values (1002, 1, '2016-02-01'), (1004, 2, '2016-01-16'),(1003, 3, '2016-03-14'),(1002, 4, '2016-04-23'),(1004, 5, '2016-01-16'),(1002, 6, '2016-01-16'),(1004, 7, '2016-01-16'),
(1004, 8, '2016-01-16'),(1002, 9, '2016-01-16'), (1004, 10, '2016-01-16');
以下SQL在MySQL中运行正常但是当我在Oracle中尝试它时，我在'dates'上得到一个'无效标识符'：
select distinct(ce.start_date) as dates,
(select count(distinct(c.customer_id))
from customers c
inner join cust_emp ce on c.customer_id = ce.cust_id
where ce.start_date < dates
and (ce.end_date > dates or (ce.deleted_yn = false or ce.deleted_yn is null))
and (c.term_date > dates or c.term_date is null)
)
from cust_emp as ce;
似乎这是因为子查询中的日期太远了。我也尝试过CTE，但这似乎有同样的问题，因为它给出了同样的错误。我如何重新编写此代码以便我可以评估Oracle中每个日期的客户数量？
答案 0 :(得分：1)
咦？
这不是你想要的吗？
select ce.dates as dates, count(distinct c.customer_id)
from cust_emp ce join
customers c
on c.customer_id = ce.cust_id
where ce.start_date < ce.dates and
(ce.end_date > ce.dates or ce.deleted_yn = false or ce.deleted_yn is null) and
(c.term_date > ce.dates or c.term_date is null)
group by ce.dates
order by ce.dates;
我不太了解子查询与select distinct的使用情况。您描述的逻辑更容易理解为简单的聚合。
我不确定dates来自哪里。它不在您的数据模型中，但它在您的示例查询中。