Reason for Column is invalid in the select list because it is not contained in either an aggregate function or the GROUP BY clause

Suppose I have the following table T:

a   b
--------
1   abc
1   def
1   ghi
2   jkl
2   mno
2   pqr

And I do the following query:

SELECT a, b
FROM T
GROUP BY a

The output should have two rows, one row where a=1 and a second row where a=2.

But what should the value of b show on each of these two rows? There are three possibilities in each case, and nothing in the query makes it clear which value to choose for b in each group. It's ambiguous.

This demonstrates the single-value rule, which prohibits the undefined results you get when you run a GROUP BY query, and you include any columns in the select-list that are neither part of the grouping criteria, nor appear in aggregate functions (SUM, MIN, MAX, etc.).

Fixing it might look like this:

SELECT a, MAX(b) AS x
FROM T
GROUP BY a

Now it's clear that you want the following result:

a   x
--------
1   ghi
2   pqr

Your query will work in MYSQL if you set to disable ONLY_FULL_GROUP_BY server mode (and by default It is). But in this case, you are using different RDBMS. So to make your query work, add all non-aggregated columns to your GROUP BY clause, eg

SELECT col1, col2, SUM(col3) totalSUM
FROM tableName
GROUP BY col1, col2

Non-Aggregated columns means the column is not pass into aggregated functions like SUM, MAX, COUNT, etc..

"All I want to do is join the tables and then group all the employees in a particular location together."

It sounds like what you want is for the output of the SQL statement to list every employee in the company, but first all the people in the Anaheim office, then the people in the Buffalo office, then the people in the Cleveland office (A, B, C, get it, obviously I don't know what locations you have).

In that case, lose the GROUP BY statement. All you need is ORDER BY loc.LocationID