SQL fetch records using group by with 3 conditions - sql

Question

I'm trying to write a query which gives me the number of patient visits by age, gender and condition(Diabetes, Hypertension etc). Get the visit count for patients having diabetes and group by gender and patients who fall between the age range of 45-54. I used Inner Join to get only the rows which are present in both tables. I get the error:
age.Age is invalid in the select list because it is not contained in
either an aggregate function or the GROUP BY clause.
Do you think I should use partition by age.age?
TABLE_A
+------------+------------+------------+
| Member_Key | VisitCount | date |
+------------+------------+------------+
| 4000 | 1 | 2014-05-07 |
| 4000 | 1 | 2014-05-09 |
| 4001 | 2 | 2014-05-08 |
+------------+------------+------------+
TABLE_B
+------------+--------------+
| Member_Key | Condition |
+------------+--------------+
| 4000 | Diabetes |
| 4000 | Diabetes |
| 4001 | Hypertension |
+------------+--------------+
TABLE_C
+------------+---------------+------------+
| Member_Key | Member_Gender | Member_DOB |
+------------+---------------+------------+
| 4000 | M | 1970-05-21 |
| 4001 | F | 1968-02-19 |
+------------+---------------+------------+
Query
SELECT c.conditions,
age.gender,
CASE
WHEN age.age BETWEEN 45 AND 54
THEN SUM(act.visitcount)
END AS age_45_54_years
FROM table_a act
INNER JOIN
(
SELECT DISTINCT
member_key,
conditions
FROM table_b
) c ON c.member_key = act.member_key
INNER JOIN
(
SELECT DISTINCT
member_key,
member_gender,
DATEPART(year, '2017-10-16')-DATEPART(year, member_dob) AS Age
FROM [table_c]
) AS age ON age.member_key = c.member_key
GROUP BY c.conditions,
age.member_gender;
Expected Output
+--------------+--------+-------------+
| Condition | Gender | TotalVisits |
+--------------+--------+-------------+
| Diabetes | M | 2 |
| Hypertension | F | 2 |
+--------------+--------+-------------+

Answer 1

You can simplify your query filtering the age on the WHERE condition
And as Sean Lange said, use DATEDADD and GETDATE() to calculate the age more accurately.
SQL DEMO
SELECT [Condition],
[Member_Gender] as [Gender],
SUM([VisitCount]) as [VisitCount]
FROM TableA A
JOIN (SELECT DISTINCT [Member_Key], [Condition]
FROM TableB) B
ON A.[Member_Key] = B.[Member_Key]
JOIN TableC C
ON A.[Member_Key] = C.[Member_Key]
WHERE [Member_DOB] BETWEEN DATEADD(year, -50 , GETDATE())
AND DATEADD(year, -45 , GETDATE())
GROUP BY [Condition], [Member_Gender]
EDIT
Have to change the WHERE condition to solve the age precision and allow index use.