MySQL子查询未返回预期结果

Question

I have a MySQL table with communities and their corresponding MLS map area. Some communities are large and take up multiple map areas.

I am attempting to do a query that returns the most common communities and their map area when passed multiple map areas.

The query I am trying for map areas 601 and 606 is:

SELECT DISTINCT(community), mapArea FROM (
    SELECT community, mapArea
    FROM single_family
    GROUP BY community
    ORDER BY COUNT(community) DESC) AS query1
WHERE mapArea LIKE '601%' OR mapArea LIKE '606%' ORDER BY community

Example single_family Table Layout (actual table has over 60k rows):

community    mapArea
Solera       606 - Henderson
Solera       606 - Henderson
Solera       204 - East
Solera       606 - Henderson
Solera       202 - East
Anthem       606 - Henderson
Green Valley 601 - Henderson
Green Valley 601 - Henderson
Green Valley 606 - Henderson
Seven Hills  606 - Henderson
Seven Hills  606 - Henderson

If I run a count on the table it shows:

community      mapArea           countCommunity
Anthem         606 - Henderson   776
Solera         606 - Henderson   58
Solera         204 - East        6
Solera         202 - East        1
Green Valley   601 - Henderson   188
Green Valley   606 - Henderson   117
Seven Hills    606 - Henderson   372

When I run the above query for map areas 601 and 606 I get the following which is correct for some communites but the community of Solera for example is not listed:

community     mapArea
Anthem        606 - Henderson
Green Valley  601 - Henderson
Seven Hills   606 - Henderson

Since Solera has the most rows with the map area being 606 - Henderson, I am wondering what is wrong in the query to why it is not being included.

Any help to why this is not returning the expected results and what I have to do to get the expected results is very much appreciated.

Answer 1

You are grouping by community , which in result, might hide mapArea lines within the grouped lines. try this instead:

SELECT community, mapArea FROM (
    SELECT community, mapArea
    FROM single_family
    WHERE mapArea LIKE '601%' OR mapArea LIKE '606%' 
    GROUP BY community
    ORDER BY COUNT(community) DESC) AS query1
ORDER BY community

also, why using DISTINCT when you're really grouping by the same column ? the subquery will result in rows with distinct values of communities. using DISTINCT will just slow down the process

Answer 2

Communities are in multiple map areas. How do you intend to handle that?

Your outer query really isn't needed. You can phrase your query as:

SELECT community, mapArea
FROM single_family
WHERE mapArea LIKE '601%' OR mapArea LIKE '606%'
GROUP BY community
ORDER BY community;

If you want all the mapArea s listed as one column, use group_concat() :

SELECT community, group_concat(mapArea) as MapAreas
FROM single_family
WHERE mapArea LIKE '601%' OR mapArea LIKE '606%'
GROUP BY community
ORDER BY community;

If you are content to have them on separate rows, include the column in the group by :

SELECT community, mapArea
FROM single_family
WHERE mapArea LIKE '601%' OR mapArea LIKE '606%'
GROUP BY community, MapArea
ORDER BY community;