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  • Efficiently store last X items in an MySQL Database

    - by Saif Bechan
    I want to store the last 3 items in an MySQL database in an efficient way. So when the 4th item is stored the first should be deleted. The way I do this not is first run a query getting the items. Than check what I should do then insert/delete. There has to be a better way to do this. Any suggestions?

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  • GROUP BY and SUM distinct date across 2 tables

    - by kenitech
    I'm not sure if this is possible in one mysql query so I might just combine the results via php. I have 2 tables: 'users' and 'billing' I'm trying to group summed activity for every date that is available in these two tables. 'users' is not historical data but 'billing' contains a record for each transaction. In this example I am showing a user's status which I'd like to sum for created date and deposit amounts that I would also like to sum by created date. I realize there is a bit of a disconnect between the data but I'd like to some all of it together and display it as seen below. This will show me an overview of all of the users by when they were created and what the current statuses are next to total transactions. I've tried UNION as well as LEFT JOIN but I can't seem to get either to work. Union example is pretty close but doesn't combine the dates into one row. ( SELECT created, SUM(status) as totalActive, NULL as totalDeposit FROM users GROUP BY created ) UNION ( SELECT created, NULL as totalActive, SUM(transactionAmount) as totalDeposit FROM billing GROUP BY created ) I've also tried using a date lookup table and joining on the dates but the SUM values are being added multiple times. note: I don't care about the userIds at all but have it in here for the example. users table (where status of '1' denotes "active") (one record for each user) created | userId | status 2010-03-01 | 10 | 0 2010-03-01 | 11 | 1 2010-03-01 | 12 | 1 2010-03-10 | 13 | 0 2010-03-12 | 14 | 1 2010-03-12 | 15 | 1 2010-03-13 | 16 | 0 2010-03-15 | 17 | 1 billing table (record created for every instance of a billing "transaction" created | userId | transactionAmount 2010-03-01 | 10 | 50 2010-03-01 | 18 | 50 2010-03-01 | 19 | 100 2010-03-10 | 89 | 55 2010-03-15 | 16 | 50 2010-03-15 | 12 | 90 2010-03-22 | 99 | 150 desired result: created | sumStatusActive | sumStatusInactive | sumTransactions 2010-03-01 | 2 | 1 | 200 2010-03-10 | 0 | 1 | 55 2010-03-12 | 2 | 0 | 0 2010-03-13 | 0 | 0 | 0 2010-03-15 | 1 | 0 | 140 2010-03-22 | 0 | 0 | 150 Table dump: CREATE TABLE IF NOT EXISTS `users` ( `created` date NOT NULL, `userId` int(11) NOT NULL, `status` smallint(6) NOT NULL ) ENGINE=MyISAM DEFAULT CHARSET=latin1; INSERT INTO `users` (`created`, `userId`, `status`) VALUES ('2010-03-01', 10, 0), ('2010-03-01', 11, 1), ('2010-03-01', 12, 1), ('2010-03-10', 13, 0), ('2010-03-12', 14, 1), ('2010-03-12', 15, 1), ('2010-03-13', 16, 0), ('2010-03-15', 17, 1); CREATE TABLE IF NOT EXISTS `billing` ( `created` date NOT NULL, `userId` int(11) NOT NULL, `transactionAmount` int(11) NOT NULL ) ENGINE=MyISAM DEFAULT CHARSET=latin1; INSERT INTO `billing` (`created`, `userId`, `transactionAmount`) VALUES ('2010-03-01', 10, 50), ('2010-03-01', 18, 50), ('2010-03-01', 19, 100), ('2010-03-10', 89, 55), ('2010-03-15', 16, 50), ('2010-03-15', 12, 90), ('2010-03-22', 99, 150);

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  • MySQL: how to index an "OR" clause

    - by JoséMi
    I'm executing the following query SELECT COUNT(*) FROM table WHERE field1='value' AND (field2 = 1000 OR field3 = 2000) There is one index over field1 and another composited over field2&field3. I see MySQL always selects the field1 index and then makes a join using the other two fields which is quite bad because it needs to join 146.000 rows. Suggestions on how to improve this? Thanks

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  • Checking if mysql user exists

    - by sergiogx
    How can I check if a user exists? Im doing an installer for a mysql database, and I need to check if a user exits, if not create user, if yes delete user and create it again. this so i can execute the script without worries. thanks.

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  • What Mysql query will return this result?

    - by Lost_in_code
    I have two tables A,B which are related to each other (simplified): A: +-------+---------+ | id | type | +-------+---------+ | 1 | apple | | 2 | orange | | 3 | banana | +-------+---------+ B: +-------+---------+-----------+ | id | a_id | rank | +-------+---------+-----------+ | 1 | 1 | 0.0 | | 2 | 1 | 7.7 | | 3 | 2 | 3.3 | | 4 | 2 | 8.8 | | 5 | 2 | 1.1 | | 6 | 3 | 3.3 | | 7 | 3 | 5.5 | | 8 | 1 | 9.5 | +-------+---------+-----------+ What mysql query will return the following result? Result +-------+---------+-----------+ | id | type | rank | +-------+---------+-----------+ | 1 | apple | 9.5 | | 2 | orange | 1.1 | | 3 | banana | 5.5 | +-------+---------+-----------+

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  • migrate a portion of a mysql table to SQLite

    - by daniel
    I have a mysql table set up like so: user_id | document 44 [blob] 44 [blob] 44 [blob] 46 [blob] I'd like to export all of user_id 44's data to an SQLite3 file. Best way to go about this without writing a script that reads the data and dumps it into a SQLite file?

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  • Mysql Trigger to select and delete

    - by Karthick
    Hi, Is this possible, can a trigger in mysql can do a select first and then based on its result do a delete?, both on the same table. Am struggling to get it right. There are duplicate entries in a table, i need to have a trigger which selects and then deletes. Any ideas or thoughts will be really helpful.

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  • Getting rows which include a value with MySQL

    - by sundowatch
    I have a MySQL query which gets including some vars like that: messages TABLE receiver cols user1 rows : 1,3,5 user2 rows : 2,3 user3 rows : 1,4 I want to get rows which includes '3' value. So I will get 'user1' and 'user2'. I tried that but naturally it doesn't work. mysql_query("SELECT * FROM messages WHERE receiver='3'"); How can I do this?

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  • MySQL: SUM in WHERE clause

    - by checcco
    Hi guys, I've got this table CREATE TABLE `subevents` ( `id` int(11) NOT NULL AUTO_INCREMENT, `title` varchar(150) DEFAULT NULL, `content` text, `class` tinyint(4) NOT NULL DEFAULT '1', PRIMARY KEY (`id`) ) ENGINE=MyISAM Each row can have a different value in the 'class' field. I'd like to select any number of rows, ordered randomly, as long as the sum of the values in the 'class' field is equal to 100. How could I accomplish it directly in the MySQL query without doing it later in PHP? Thanks everybody!

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  • MySQL One to Many order by number found in joined table

    - by Finbarr
    Two tables: table_a ------- table_a_id: (primary, int) table_b ------- table_a_id: (index, int, from table_a) table_b_value: (varchar) A one to many relationship between table_a_id and table_b_value. Given a query like this: SELECT DISTINCT(table_a_id) FROM table_a JOIN table_b ON table_a.table_a_id=table_b.table_a_id I want to order by the number of occurrences of table_a_id in table_b. I'm not really sure how to write this in MySQL.

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  • MySQL - What is the correct primary key method

    - by Hammerstein
    I'm starting to develop an application using MySQL and although I've developed apps before using databases, I've normally gone to the incrementing id method. The other day I was reading a posting somewhere and saw someone being picked apart for this, for not properly "normalising the database". I'm not a big database person, but I wanted to make sure I'm doing this right. Any ideas, help / guidance?

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