greatest-n-per-group

问题 How can you join between a table with a sparse number of dates and another table with an exhaustive number of dates such that the gaps between the sparse dates take the values of the previous sparse date? Illustrative example: PRICE table (sparse dates): date itemid price 2008-12-04 1 $1 2008-12-11 1 $3 2008-12-15 1 $7 VOLUME table (exhaustive dates): date itemid volume_amt 2008-12-04 1 12345 2008-12-05 1 23456 2008-12-08 1 34567 2008-12-09 1 ... 2008-12-10 1 2008-12-11 1 2008-12-12 1 2008-12

问题 I have a table that looks similar to this: credit +---------+----------------+-------------+--------------+-------------------------+ | id (PK) | person_id (FK) | transaction | total credit | date_time | +---------+----------------+-------------+--------------+-------------------------+ | 345 | 1 | -1.00 | 34.50 | 2018-08-29 12:00:00.000 | | 897 | 1 | 5.45 | 39.95 | 2018-08-29 12:34:00.000 | | 378 | 2 | 0.01 | 0.01 | 2018-08-29 08:00:00.000 | | 789 | 2 | 20.00 | 20.01 | 2018-08-29 09:00:00

问题 I have a table that looks similar to this: credit +---------+----------------+-------------+--------------+-------------------------+ | id (PK) | person_id (FK) | transaction | total credit | date_time | +---------+----------------+-------------+--------------+-------------------------+ | 345 | 1 | -1.00 | 34.50 | 2018-08-29 12:00:00.000 | | 897 | 1 | 5.45 | 39.95 | 2018-08-29 12:34:00.000 | | 378 | 2 | 0.01 | 0.01 | 2018-08-29 08:00:00.000 | | 789 | 2 | 20.00 | 20.01 | 2018-08-29 09:00:00

问题 I have a table of user access sessions which records website visitor activity: accessid, userid, date, time, url I'm trying to retrieve all distinct sessions for userid 1234, as well as the earliest date and time for each of those distinct sessions. SELECT DISTINCT accessid, date, time FROM accesslog WHERE userid = '1234' GROUP BY accessid This gives me the date and time of a random row within each distinct accessid. I've read a number of posts recommending the use of min() and max(), so I

问题 SOLVED All hail StackOverlow! While I was gone, people left 2 solutions (thanks guys--what is the protocol for handing out karma for two working solutions?) Here is the solution that I came back to post. it is derived from yet ANOTHER StackOver solution: How to fetch the first and last record of a grouped record in a MySQL query with aggregate functions? ...and my adaptation is: SELECT DATE_FORMAT(`DTE`, "%m/%d/%Y") AS trading_day, MIN(`PRICE`) AS min_price, MAX(`PRICE`) AS max_price,

问题 I have the following table. test_type | brand | model | band | firmware_version | avg_throughput -----------+---------+--------+------+-----------------+---------------- 1client | Linksys | N600 | 5ghz | 1 | 66.94 1client | Linksys | N600 | 5ghz | 2 | 94.98 1client | Linksys | N600 | 5ghz | 4 | 132.40 1client | Linksys | EA6500 | 5ghz | 1 | 216.46 1client | Linksys | EA6500 | 5ghz | 2 | 176.79 1client | Linksys | EA6500 | 5ghz | 4 | 191.44 I'd like to select the avg_throughput of each model

问题 I have the following table. test_type | brand | model | band | firmware_version | avg_throughput -----------+---------+--------+------+-----------------+---------------- 1client | Linksys | N600 | 5ghz | 1 | 66.94 1client | Linksys | N600 | 5ghz | 2 | 94.98 1client | Linksys | N600 | 5ghz | 4 | 132.40 1client | Linksys | EA6500 | 5ghz | 1 | 216.46 1client | Linksys | EA6500 | 5ghz | 2 | 176.79 1client | Linksys | EA6500 | 5ghz | 4 | 191.44 I'd like to select the avg_throughput of each model

问题 I have a table within my database that has many records, some records share the same value for one of the columns. e.g. | id | name | software | ______________________________ | 1 | john | photoshop | | 2 | paul | photoshop | | 3 | gary | textmate | | 4 | ade | fireworks | | 5 | fred | textmate | | 6 | bob | photoshop | I would like to return the value of the most common occurring piece of software, by using an SQL statement. So in the example above the required SQL statement would return

问题 SELECT MAX('time'), c_id, message, state, time FROM message WHERE receive = 1 GROUP BY c_id I have a mysql query, I try to select the last row of each group, but it's not working. c_id is the group. It select the first row of each group now. 回答1: First, you should not escape the column name with single quote since it is not string literal. Second, you can do subquery which separately get the latest time for every c_id and join it back with the original table to get the other columns. SELECT a

问题 I have some kind of impossible request :). I have a table where one of the columns is named type . I would like to SELECT 3 records for each type in that column. Is that possible? Note also that I'm using MySQL and Sphinx. UPDATE: Table structure id title type 1 AAAA string1 2 CCCC string2 3 EEEE string2 4 DDDD string2 5 FFFF string2 6 BBBB string2 6 BBBB string2 What I want my MySQL to return is (up to 3 records for each type ordered by title): id title type 1 AAAA string1 6 BBBB string2 2