使用联接的MySQL查询

Question

I have 2 tables - 'cityname' and 'citymoisture'.

'cityname' has 2 columns:  
-city_ID <- integer and primary key that increments automatically  
-city_full_name <- character name i.e. boston, toronto, new york city etc...  

'citymoisture' has 7 columns:  
-city_ID <- tied to the city_ID field via a Foreign Key  
-date  
-time  
-open  
-high  
-low  
-close  

What I want to do is -

Query for any of open, high, low and close in the moisture table by specifying the name of the city and date range.

The following query works:

USE moisturedb  
SELECT citymoisture.date, citymoisture.time, citymoisture.close  
FROM citymoisture  
WHERE (citymoisture.date BETWEEN '2011/03/09' AND '2011/03/14') AND citymoisture.city_id=5;

But this only references the 'citymoisture' table. I have a front end application that allows users to select the city name so in a sense I want to run a joined query that drops the results based on the city_full_name column in the cityname table.

I've tinkered around with a few join queries without success. I have also spent the last several hours searching through join query examples without any success.

I greatly appreciate your help.

As a follow-up to Nikhil's request here is a sample output of the query suggested.

| 2011-03-10   | 03:38:00     | 0.918 |
| 2011-03-10   | 03:39:00     | 0.897 |
| 2011-03-10   | 03:40:00     | 0.917 |
| 2011-03-10   | 03:41:00     | 0.915 |
| 2011-03-10   | 03:42:00     | 0.914 |
| 2011-03-10   | 03:43:00     | 0.924 |
| 2011-03-10   | 03:44:00     | 0.922 |
| 2011-03-10   | 03:45:00     | 0.922 |
| 2011-03-10   | 03:46:00     | 0.923 |
| 2011-03-10   | 03:47:00     | 0.935 |
| 2011-03-10   | 03:48:00     | 0.953 |
| 2011-03-10   | 03:49:00     | 0.927 |  
| 2011-03-10   | 03:50:00     | 0.962 |  
| 2011-03-10   | 03:51:00     | 0.914 |  
| 2011-03-10   | 03:52:00     | 0.935 |  
+--------------+--------------+-------+  
14770 rows in set (2 min 28.80 sec)  

Where the 3rd column is the moisture data. The values for each city in the query are knitted together in the sense that they are stacked one after the other. I would very much like the following output where the moisture data for each city appear in separate columns:

2011-03-10  03:49:00  0.935  0.935  0.935  .....  
2011-03-10  03:50:00  0.935  0.935  0.935  .....  
2011-03-10  03:51:00  0.935  0.935  0.935  .....  
2011-03-10  03:52:00  0.935  0.935  0.935  .....  
2011-03-10  03:53:00  0.935  0.935  0.935  .....  
2011-03-10  03:54:00  0.935  0.935  0.935  .....  

Answer 1

Try this:

USE moisturedb  
SELECT citymoisture.date, citymoisture.time, citymoisture.close  
FROM citymoisture INNER JOIN cityname ON cityname.city_ID=citymoisture.city_ID
WHERE (citymoisture.date BETWEEN '2011/03/09' AND '2011/03/14') AND cityname.city_full_name='boston'

Answer 2

SELECT citymoisture.date, citymoisture.time, citymoisture.close 
FROM citymoisture LEFT JOIN cityname USING (city_ID)
WHERE (citymoisture.date BETWEEN '2011/03/09' AND '2011/03/14')
AND citymoisture.city_full_name='boston';

However, I think the query that you have posted in your question is the one that should be used. You must be having a front-end with a drop-down for the user to select the city. That drop-down can be populated using cityname such that the city_ID is sent back to the server when the user selects a city. You can then use the city_ID in the original query that you have posted. For reference, check the value attribute of the option tag here .