Churn Rate From Contract Start & End Dates - sql

Question

I am trying to calculate the churn rate of customer and all I have to play with is contract start & end dates.
When the date year is 9999 it just means they are still a customer and I would like to consider account only who have a tenure of more than 3 months (as in have been with the company for 3 or more months).
CREATE TABLE #temp
(
ACCOUNT varchar(20)NOT NULL
,CONTRACT_START_DATE DATETIME NOT NULL
,CONTRACT_END_DATE DATETIME NOT NULL
)
;
INSERT INTO #temp
VALUES('64074558792','20160729','20170805');
INSERT INTO #temp
VALUES('54654654664','20160810','20170110');
INSERT INTO #temp
VALUES('21454654764','20160112','20160812');
INSERT INTO #temp
VALUES('21654765134','20160101','20161231');
INSERT INTO #temp
VALUES('13214868794','20160811','99991231');
INSERT INTO #temp
VALUES ('88321546894','20160427','20160627');
SELECT *,
CASE WHEN CONTRACT_END_DATE <> '99991231' THEN DATEDIFF(DAY, CONTRACT_START_DATE,CONTRACT_END_DATE) ELSE null END AS TENURE
FROM #temp

Answer 1

The below will work for a single reporting year. There's a few things it seems like you're trying to get:
-Number of customers who stay longer than x months
-% of customers that stay for more than x months
-% of customers lost during the year
DECLARE #records TABLE
(
ACCOUNT varchar(20)NOT NULL
,CONTRACT_START_DATE DATETIME NOT NULL
,CONTRACT_END_DATE DATETIME NOT NULL
);
DECLARE #ReportingYear INT = 2016;
DECLARE #MinTenureMonths INT = 3;
INSERT INTO #records
VALUES('64074558792','20160729','20170805'),
('54654654664','20160810','20170110'),
('21454654764','20160112','20160812'),
('21654765134','20151011','20161231'),--I changed this one
('13214868794','20160811','99991231'),
('88321546894','20160427','20160627');
SELECT *,
[CustomerGained] = IIF(YEAR(CONTRACT_START_DATE) = #ReportingYear,1,0),
[CustomerLost] = IIF(YEAR(CONTRACT_END_DATE) = #ReportingYear,1,0) ,
[ExistingCustomer] = IIF(CONTRACT_START_DATE < DATEFROMPARTS(#ReportingYear,1,1)
AND CONTRACT_END_DATE > DATEFROMPARTS(#ReportingYear,12,31), 1, 0),
[CurrentCustomer] = IIF(CONTRACT_END_DATE = '99991231 00:00:00.000',1,0),
[MinTenureExceeded] = IIF(DATEDIFF(MONTH, CONTRACT_START_DATE, CONTRACT_END_DATE) >= #MinTenureMonths,1,0)
FROM #records;
With recordCTE AS
(
SELECT
[CustomersGained] = SUM(IIF(YEAR(CONTRACT_START_DATE) = #ReportingYear,1,0)),
[CustomersLost] = SUM(IIF(YEAR(CONTRACT_END_DATE) = #ReportingYear,1,0)),
[MinTenureExceeded] = SUM(IIF(DATEDIFF(MONTH, CONTRACT_START_DATE, CONTRACT_END_DATE) >= #MinTenureMonths,1,0)),
[ExistingCustomers] = SUM(IIF(CONTRACT_START_DATE < DATEFROMPARTS(#ReportingYear,1,1)
AND CONTRACT_END_DATE > DATEFROMPARTS(#ReportingYear,12,31), 1, 0)),
[CurrentCustomer] = SUM(IIF(CONTRACT_END_DATE = '99991231 00:00:00.000',1,0)),
[TotalCustomers] = COUNT(1)
FROM #records
)
SELECT c.CustomersGained,
c.CustomersLost,
c.MinTenureExceeded,
c.ExistingCustomers,
[% Lost] = CAST(((c.CustomersLost * 1.0) / c.TotalCustomers) * 100 AS DECIMAL(14,2)),
[% Gained] = CAST(((c.CustomersGained * 1.0) / c.TotalCustomers) * 100 AS DECIMAL(14,2))
FROM recordCTE c;
You'll need to decide whether you're just looking for a single reporting year, a reporting period, or in total for everything. If you want everything, just do all the calcs using CurrentCustomers instead.