MYSQL divide results from multiple subqueries with multiple rows

问题

I have two queries, the first one generating a table like

SELECT COUNT(channel) AS messages FROM Chats WHERE message LIKE '%word%' GROUP BY UNIX_TIMESTAMP(time) DIV 3600
+-----+
| 123 |
| 127 |
| 332 |
| 219 |
+-----+

and the second one

SELECT COUNT(channel) AS messages FROM Chats GROUP BY UNIX_TIMESTAMP(time) DIV 3600
+-----+
| 222 |
| 579 |
| 590 |
| 377 |
+-----+

Now I would like to divide all results from the first table by the corresponding value in the second one (results rounded, had to calculate it manually):

+------+
| 0.55 | #123/222
| 0.46 | #127/279
| 0.56 | #332/590
| 0.58 | #219/377
+------+

回答1:

Here's one way you can accomplish the whole thing by the following query:

SELECT 
(dividendTable.messages / divisorTable.messages) AS result
FROM
(
    SELECT 
    firstTable.messages,
    @rn1 := @rn1 + 1 AS row_number
    FROM 
    (
        SELECT
            COUNT(channel) AS messages
        FROM Chats
        WHERE   message LIKE '%word%'
        GROUP BY    UNIX_TIMESTAMP(time) DIV 3600
    ) FirstTable, (SELECT @rn1 := 0) var1
) AS dividendTable
INNER JOIN
(   
    SELECT 
    secondTable.messages,
    @rn2 := @rn2 + 1 AS row_number
    FROM
    (
        SELECT 
            COUNT(channel) AS messages 
        FROM Chats 
        GROUP BY UNIX_TIMESTAMP(time) DIV 3600
    ) secondTable, (SELECT @rn2 := 0) var2
) AS divisorTable
ON dividendTable.row_number = divisorTable.row_number;

Note:

If you want the result rounded up to 2 digits after the decimal point then use the following as the first line of the query:

SELECT
ROUND((dividendTable.messages / divisorTable.messages),2) AS result

Demo Here

Caution: You haven't used any ORDER BY in your query. You might get random behavior.

来源：https://stackoverflow.com/questions/36233810/mysql-divide-results-from-multiple-subqueries-with-multiple-rows

标签

mysql

subquery