SQL Group By Query - sql

Question

I have the following table with one column ArbPlWPos:
+------------+
+ IH-MKE +
+ IH-MKEEA +
+ IH-MKEEB +
+ IH-MKEPE +
+ IH-MKEPM +
+ IH-MVKE1 +
+ IH-MVKM1 +
+------------+
I can run a statement in MS Access which groups by the first 6 letters:
SELECT left(ArbPlWPos, 6), count(left(ArbPlWPos, 6))
FROM my_table
GROUP BY left(ArbPlWPos, 6)
+------------+------+
+ IH-MKE + 10 +
+ IH-MKM + 20 +
+ IH-MVK + 30 +
+------------+------+
How to include the IH-MVK into the IH-MKE, so the result should be:
+------------+------+
+ IH-MKE + 40 +
+ IH-MKM + 20 +
+------------+------+
Is this somehow possible with SQL/Access?

Answer 1

In MS Access, you can do this using a conditional expression, iif():
SELECT iif(ArbPlWPos like "IH-MVK*", "IH-MKE", left(ArbPlWPos, 6)),
count(*)
FROM TABLE
GROUP BY iif(ArbPlWPos like "IH-MVK*", "IH-MKE", left(ArbPlWPos, 6));

Answer 2

You can group by any expression, but you are to repeat it after SELECT (is you need) and after GROUP BY as you did with an usual column. For example:
SELECT my_function_or_expression(column_A, column_B), count(1)
FROM my_table
GROUP BY my_function_or_expression(column_A, column_B);
In your case it will be:
SELECT
CASE WHEN left(ArbPlWPos, 6) = 'IH-MVK'
THEN 'IH-MKE'
ELSE left(ArbPlWPos, 6) END AS cutArbPlWPos,
count(1) AS amount
FROM my_table
GROUP BY CASE WHEN left(ArbPlWPos, 6) = 'IH-MVK'
THEN 'IH-MKE'
ELSE left(ArbPlWPos, 6) END;
You can also simplify it using subquery.
SELECT cutArbPlWPos, count(1)
FROM (SELECT
CASE WHEN left(ArbPlWPos, 6) = 'IH-MVK'
THEN 'IH-MKE'
ELSE left(ArbPlWPos, 6) END AS cutArbPlWPos
FROM my_table
)
GROUP BY cutArbPlWPos;