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• how to avoid sub-query to gain performance

  - by chun

  hi i have a reporting query which have 2 long sub-query SELECT r1.code_centre, r1.libelle_centre, r1.id_equipe, r1.equipe, r1.id_file_attente, r1.libelle_file_attente,r1.id_date, r1.tranche, r1.id_granularite_de_periode,r1.granularite, r1.ContactsTraites, r1.ContactsenParcage, r1.ContactsenComm, r1.DureeTraitementContacts, r1.DureeComm, r1.DureeParcage, r2.AgentsConnectes, r2.DureeConnexion, r2.DureeTraitementAgents, r2.DureePostTraitement FROM ( SELECT cc.id_centre_contact, cc.code_centre, cc.libelle_centre, a.id_equipe, a.equipe, a.id_file_attente, f.libelle_file_attente, a.id_date, g.tranche, g.id_granularite_de_periode, g.granularite, sum(Nb_Contacts_Traites) as ContactsTraites, sum(Nb_Contacts_en_Parcage) as ContactsenParcage, sum(Nb_Contacts_en_Communication) as ContactsenComm, sum(Duree_Traitement/1000) as DureeTraitementContacts, sum(Duree_Communication / 1000 + Duree_Conference / 1000 + Duree_Com_Interagent / 1000) as DureeComm, sum(Duree_Parcage/1000) as DureeParcage FROM agr_synthese_activite_media_fa_agent a, centre_contact cc, direction_contact dc, granularite_de_periode g, media m, file_attente f WHERE m.id_media = a.id_media AND cc.id_centre_contact = a.id_centre_contact AND a.id_direction_contact = dc.id_direction_contact AND dc.direction_contact ='INCOMING' AND a.id_file_attente = f.id_file_attente AND m.media = 'PHONE' AND ( ( g.valeur_min = date_format(a.id_date,'%d/%m') and g.granularite = 'Jour') or ( g.granularite = 'Heure' and a.id_th_heure = g.id_granularite_de_periode) ) GROUP by cc.id_centre_contact, a.id_equipe, a.id_file_attente, a.id_date, g.tranche, g.id_granularite_de_periode) r1, ( (SELECT cc.id_centre_contact,cc.code_centre, cc.libelle_centre, a.id_equipe, a.equipe, a.id_date, g.tranche, g.id_granularite_de_periode,g.granularite, count(distinct a.id_agent) as AgentsConnectes, sum(Duree_Connexion / 1000) as DureeConnexion, sum(Duree_en_Traitement / 1000) as DureeTraitementAgents, sum(Duree_en_PostTraitement / 1000) as DureePostTraitement FROM activite_agent a, centre_contact cc, granularite_de_periode g WHERE ( g.valeur_min = date_format(a.id_date,'%d/%m') and g.granularite = 'Jour') AND cc.id_centre_contact = a.id_centre_contact GROUP BY cc.id_centre_contact, a.id_equipe, a.id_date, g.tranche, g.id_granularite_de_periode ) UNION (SELECT cc.id_centre_contact,cc.code_centre, cc.libelle_centre, a.id_equipe, a.equipe, a.id_date, g.tranche, g.id_granularite_de_periode,g.granularite, count(distinct a.id_agent) as AgentsConnectes, sum(Duree_Connexion / 1000) as DureeConnexion, sum(Duree_en_Traitement / 1000) as DureeTraitementAgents, sum(Duree_en_PostTraitement / 1000) as DureePostTraitement FROM activite_agent a, centre_contact cc, granularite_de_periode g WHERE ( g.granularite = 'Heure' AND a.id_th_heure = g.id_granularite_de_periode) AND cc.id_centre_contact = a.id_centre_contact GROUP BY cc.id_centre_contact,a.id_equipe, a.id_date, g.tranche, g.id_granularite_de_periode) ) r2 WHERE r1.id_centre_contact = r2.id_centre_contact AND r1.id_equipe = r2.id_equipe AND r1.id_date = r2.id_date AND r1.tranche = r2.tranche AND r1.id_granularite_de_periode = r2.id_granularite_de_periode GROUP BY r1.id_centre_contact , r1.id_equipe, r1.id_file_attente, r1.id_date, r1.tranche, r1.id_granularite_de_periode ORDER BY r1.code_centre, r1.libelle_centre, r1.equipe, r1.libelle_file_attente, r1.id_date, r1.id_granularite_de_periode,r1.tranche the EXPLAIN shows | id | select_type | table | type| possible_keys | key | key_len | ref| rows | Extra | '1', 'PRIMARY', '<derived3>', 'ALL', NULL, NULL, NULL, NULL, '2520', 'Using temporary; Using filesort' '1', 'PRIMARY', '<derived2>', 'ALL', NULL, NULL, NULL, NULL, '4378', 'Using where; Using join buffer' '3', 'DERIVED', 'a', 'ALL', 'fk_Activite_Agent_centre_contact', NULL, NULL, NULL, '83433', 'Using temporary; Using filesort' '3', 'DERIVED', 'g', 'ref', 'Index_granularite,Index_Valeur_min', 'Index_Valeur_min', '23', 'func', '1', 'Using where' '3', 'DERIVED', 'cc', 'ALL', 'PRIMARY', NULL, NULL, NULL, '6', 'Using where; Using join buffer' '4', 'UNION', 'g', 'ref', 'PRIMARY,Index_granularite', 'Index_granularite', '23', '', '24', 'Using where; Using temporary; Using filesort' '4', 'UNION', 'a', 'ref', 'fk_Activite_Agent_centre_contact,fk_activite_agent_TH_heure', 'fk_activite_agent_TH_heure', '5', 'reporting_acd.g.Id_Granularite_de_periode', '2979', 'Using where' '4', 'UNION', 'cc', 'ALL', 'PRIMARY', NULL, NULL, NULL, '6', 'Using where; Using join buffer' NULL, 'UNION RESULT', '<union3,4>', 'ALL', NULL, NULL, NULL, NULL, NULL, '' '2', 'DERIVED', 'g', 'range', 'PRIMARY,Index_granularite,Index_Valeur_min', 'Index_granularite', '23', NULL, '389', 'Using where; Using temporary; Using filesort' '2', 'DERIVED', 'a', 'ALL', 'fk_agr_synthese_activite_media_fa_agent_centre_contact,fk_agr_synthese_activite_media_fa_agent_direction_contact,fk_agr_synthese_activite_media_fa_agent_file_attente,fk_agr_synthese_activite_media_fa_agent_media,fk_agr_synthese_activite_media_fa_agent_th_heure', NULL, NULL, NULL, '20903', 'Using where; Using join buffer' '2', 'DERIVED', 'cc', 'eq_ref', 'PRIMARY', 'PRIMARY', '4', 'reporting_acd.a.Id_Centre_Contact', '1', '' '2', 'DERIVED', 'f', 'eq_ref', 'PRIMARY', 'PRIMARY', '4', 'reporting_acd.a.Id_File_Attente', '1', '' '2', 'DERIVED', 'dc', 'eq_ref', 'PRIMARY', 'PRIMARY', '4', 'reporting_acd.a.Id_Direction_Contact', '1', 'Using where' '2', 'DERIVED', 'm', 'eq_ref', 'PRIMARY', 'PRIMARY', '4', 'reporting_acd.a.Id_Media', '1', 'Using where' don't know it very clear, but i think is the problem of seems it take full scaning than i change all the sub-query to views(create view as select sub-query), and the result is the same thanks for any advice

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• Rails ActiveRecord friendly code from a Complex Join, Sum, and Group query

  - by Chad M

  PROBLEM Hello, I am having no luck trying to break down this SQL statement into ActiveRecord/Rails friendly code and I'd like to learn how I can avoid a find_by_sql statement in this situation. Scenario I have users that create audits when they perform an action. Each audit is of a specific audit_activity. Each audit_activity is worth a certain number of points, based on score_weight. I need to find the total scores of each user, based on their total accumulated audit_activity score_weights. Eventually I'll need to rank them which means adding a sort to this as well. My Code Here is my sql and simplified versions of the tables in question. Any thoughts? SQL with full column names (for clarity) SELECT users.id, u.email, SUM(audit_activity.score_weight) FROM users JOIN audits ON users.id = audits.user_id JOIN audit_activities ON audit_activities.id = audits.audit_activity_id GROUP BY users.id; Models: User, Audit, AuditActivity User fields: id, email class User < ActiveRecord::Base include Clearance::User has_many :audits end Audit fields: id, user_id, audit_activity_id class Audit < ActiveRecord::Base belongs_to :user belongs_to :audit_activity end AuditActivity fields: id, score_weight class AuditActivity < ActiveRecord::Base has_many :audits end Example Data Here is a set of SQL statements so you can play with similar data I'm working with and see what comes up when the concerned query is run. You should just be able to copy/paste the whole thing into a database query browser. CREATE TABLE users( id INTEGER NOT NULL, email TEXT (25), PRIMARY KEY (id) ); CREATE TABLE audits( id INTEGER NOT NULL, user_id INTEGER, audit_activity_id INTEGER, PRIMARY KEY (id) ); CREATE TABLE audit_activities( id INTEGER NOT NULL, score_weight INTEGER, PRIMARY KEY (id) ); INSERT INTO users(id, email) VALUES(1, "[email protected]"); INSERT INTO users(id, email) VALUES(2, "[email protected]"); INSERT INTO users(id, email) VALUES(3, "[email protected]"); INSERT INTO audits(id, user_id, audit_activity_id) VALUES(1, 1, 1); INSERT INTO audits(id, user_id, audit_activity_id) VALUES(2, 1, 2); INSERT INTO audits(id, user_id, audit_activity_id) VALUES(3, 1, 1); INSERT INTO audits(id, user_id, audit_activity_id) VALUES(4, 1, 3); INSERT INTO audits(id, user_id, audit_activity_id) VALUES(5, 1, 1); INSERT INTO audits(id, user_id, audit_activity_id) VALUES(6, 1, 4); INSERT INTO audits(id, user_id, audit_activity_id) VALUES(7, 2, 4); INSERT INTO audits(id, user_id, audit_activity_id) VALUES(8, 2, 4); INSERT INTO audits(id, user_id, audit_activity_id) VALUES(9, 2, 4); INSERT INTO audits(id, user_id, audit_activity_id) VALUES(10, 3, 3); INSERT INTO audits(id, user_id, audit_activity_id) VALUES(11, 3, 2); INSERT INTO audits(id, user_id, audit_activity_id) VALUES(12, 3, 2); INSERT INTO audits(id, user_id, audit_activity_id) VALUES(13, 3, 2); INSERT INTO audits(id, user_id, audit_activity_id) VALUES(14, 3, 3); INSERT INTO audits(id, user_id, audit_activity_id) VALUES(15, 3, 1); INSERT INTO audits(id, user_id, audit_activity_id) VALUES(16, 3, 1); INSERT INTO audit_activities(id, score_weight) VALUES(1, 1); INSERT INTO audit_activities(id, score_weight) VALUES(2, 2); INSERT INTO audit_activities(id, score_weight) VALUES(3, 7); INSERT INTO audit_activities(id, score_weight) VALUES(4, 11); The Query Again, here is the query. SELECT u.id, u.email, SUM(aa.score_weight) FROM users u JOIN audits a ON u.id = a.user_id JOIN audit_activities aa ON aa.id = a.audit_activity_id GROUP BY u.id; Many Thanks, Chad

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• insert multiple rows via a php array into mysql

  - by toofarsideways

  I'm passing a large dataset into a mysql table via php using insert commands and I'm wondering if its possible to insert approximately 1000 rows at a time via a query other than appending each value on the end of an mile long string and then executing it. I am using the codeigniter framework so its functions are also available to me.

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• How to know the exact statement fired in Data app block?

  - by AJ

  Hi We are using "Enterprise Library Data Access Application Block" to access SQL Server database. In DataAccess layer, we are calling application block's API. Internally it must be resolving the command and parameters into SQL statement. How can I know what SQL query goes to database? Thanks AJ

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• How to get a table creation script in MySQL Workbench?

  - by estourodepilha.com

  I am rolling back to MySQL GUI Tools' MySQL Query Browser since I can't find the shortcut to get a table's creation script in MySQL Workbench.

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• Calculating Percentile Using Cumulative Data in MySQL

  - by Kirk

  What should the percentile ranks be for each of these records and is there a MySQL query I can run to calculate the percentile? id score cumulative_score percentile 1 100 100 ? 2 50 150 ? 3 25 175 ? 4 25 200 ? 5 10 210 ?

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• fetch_all or fetch_assoc MySQLi statement

  - by all-R

  Hi, is it possible to use the fetch_all(), fetch_assoc() etc. from the the MySQLi_Result class with a prepared statement from the MySQLi_STMT class? I've done it using the query() method in the Mysqli class (and by escaping trough mysqli_real_escape_string()), but not using statements with binding parameters. I'm considering using PDO thanks!

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• Linq Distinct on list

  - by BahaiResearch.com

  I have a list like this: List people age name 1 bob 1 sam 7 fred 7 tom 8 sally I need to do a linq query on people and get an int of the number distinct ages (3) int distinctAges = people.SomeLinq(); how? how?

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• MySQL queries - how expensive are they really?

  - by incrediman

  I've heard that mysql queries are very expensive, and that you should avoid at all costs making too many of them. I'm developing a site that will be used by quite a few people, and I'm wondering: How expensive are mysql queries actually? If I have 400,000 people in my database, how expensive is it to query it for one of them? How close attention do I need to pay that I don't make too many queries per client request?

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• Monitoring used connections on mysql to debug 'too many connections'

  - by Nir

  On LAMP production server I get the 'too many connections' error from MYSQL occasionally, I want to add monitoring to find if the reason is that I exceed the max-connections limit. My question: How can I query from mysql or from mysqladmin the current number of used connections? (I noticed that show status gives total connections and not the currently used ones.)

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• Will Google index my site like this?

  - by alex

  Suppose I have a URL in my query string. Someone told me that Google does not like it because they believe we are pulling content from another server. http://mydomain.com/?id=http://abc.com

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• Designing a game database

  - by Ronald

  I'm trying to design a database to record game histories for a game I'm working on. I have 3 different tables: users, gamehistories, and gamescores. Columns for tables: users: uid, displayname, email gamehistories: gid, pubID, start (datetime), end (datetime) gamescores: gid, uid, score I am trying to produce the following result set given a userID (uid): Opponent's displayname, my score, opponent's score, duration Any ideas? Is my design ok? How can I query these tables to get game histories for a given uid?

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• Variables are "lost" somewhere, then reappear... all with no error thrown.

  - by rob - not a robber

  Hi All, I'm probably going to make myself look like a fool with my horrible scripting but here we go. I have a form that I am collecting a bunch of checkbox info from using a binary method. ON/SET=1 !ISSET=0 Anyway, all seems to be going as planned except for the query bit. When I run the script, it runs through and throws no errors, but it's not doing what I think I am telling it to. I've hard coded the values in the query and left them in the script and it DOES update the DB. I've also tried echoing all the needed variables after the script runs and exiting right after so I can audit them... and they're all there. Here's an example. ####FEATURES RECORD UPDATE ### HERE I DECIDE TO RUN THE SCRIPT BASED ON WHETHER AN IMAGE BUTTON WAS USED if (isset($_POST["button_x"])) { ### HERE I AM ASSIGNING 1 OR 0 TO A VAR BASED ON WHTER THE CHECKBOX WAS SET if (isset($_POST["pool"])) $pool=1; if (!isset($_POST["pool"])) $pool=0; if (isset($_POST["darts"])) $darts=1; if (!isset($_POST["darts"])) $darts=0; if (isset($_POST["karaoke"])) $karaoke=1; if (!isset($_POST["karaoke"])) $karaoke=0; if (isset($_POST["trivia"])) $trivia=1; if (!isset($_POST["trivia"])) $trivia=0; if (isset($_POST["wii"])) $wii=1; if (!isset($_POST["wii"])) $wii=0; if (isset($_POST["guitarhero"])) $guitarhero=1; if (!isset($_POST["guitarhero"])) $guitarhero=0; if (isset($_POST["megatouch"])) $megatouch=1; if (!isset($_POST["megatouch"])) $megatouch=0; if (isset($_POST["arcade"])) $arcade=1; if (!isset($_POST["arcade"])) $arcade=0; if (isset($_POST["jukebox"])) $jukebox=1; if (!isset($_POST["jukebox"])) $jukebox=0; if (isset($_POST["dancefloor"])) $dancefloor=1; if (!isset($_POST["dancefloor"])) $dancefloor=0; ### I'VE DONE LOADS OF PERMUTATIONS HERE... HARD SET THE 1/0 VARS AND LEFT THE $estab_id TO BE PICKED UP. SET THE $estab_id AND LEFT THE COLUMN DATA TO BE PICKED UP. ALL NO GOOD. IT _DOES_ WORK IF I HARD SET ALL VARS THOUGH mysql_query("UPDATE thedatabase SET pool_table='$pool', darts='$darts', karoke='$karaoke', trivia='$trivia', wii='$wii', megatouch='$megatouch', guitar_hero='$guitarhero', arcade_games='$arcade', dancefloor='$dancefloor' WHERE establishment_id='22'"); ###WEIRD THING HERE IS IF I ECHO THE VARS AT THIS POINT AND THEN EXIT(); they all show up as intended. header("location:theadminfilething.php"); exit(); THANKS ALL!!!

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• sql: Group by x,y,z; return grouped by x,y with lowest f(z)

  - by Sai Emrys

  This is for http://cssfingerprint.com I collect timing stats about how fast the different methods I use perform on different browsers, etc., so that I can optimize the scraping speed. Separately, I have a report about what each method returns for a handful of URLs with known-correct values, so that I can tell which methods are bogus on which browsers. (Each is different, alas.) The related tables look like this: CREATE TABLE `browser_tests` ( `id` int(11) NOT NULL AUTO_INCREMENT, `bogus` tinyint(1) DEFAULT NULL, `result` tinyint(1) DEFAULT NULL, `method` varchar(255) DEFAULT NULL, `url` varchar(255) DEFAULT NULL, `os` varchar(255) DEFAULT NULL, `browser` varchar(255) DEFAULT NULL, `version` varchar(255) DEFAULT NULL, `created_at` datetime DEFAULT NULL, `updated_at` datetime DEFAULT NULL, `user_agent` varchar(255) DEFAULT NULL, PRIMARY KEY (`id`) ) ENGINE=InnoDB AUTO_INCREMENT=33784 DEFAULT CHARSET=latin1 CREATE TABLE `method_timings` ( `id` int(11) NOT NULL AUTO_INCREMENT, `method` varchar(255) DEFAULT NULL, `batch_size` int(11) DEFAULT NULL, `timing` int(11) DEFAULT NULL, `os` varchar(255) DEFAULT NULL, `browser` varchar(255) DEFAULT NULL, `version` varchar(255) DEFAULT NULL, `user_agent` varchar(255) DEFAULT NULL, `created_at` datetime DEFAULT NULL, `updated_at` datetime DEFAULT NULL, PRIMARY KEY (`id`) ) ENGINE=InnoDB AUTO_INCREMENT=28849 DEFAULT CHARSET=latin1 (user_agent is broken down pre-insert into browser, version, and os from a small list of recognized values using regex; I keep the original user-agent string just in case.) I have a query like this that tells me the average timing for every non-bogus browser / version / method tuple: select c, avg(bogus) as bog, timing, method, browser, version from browser_tests as b inner join ( select count(*) as c, round(avg(timing)) as timing, method, browser, version from method_timings group by browser, version, method having c > 10 order by browser, version, timing ) as t using (browser, version, method) group by browser, version, method having bog < 1 order by browser, version, timing; Which returns something like: c bog tim method browser version 88 0.8333 184 reuse_insert Chrome 4.0.249.89 18 0.0000 238 mass_insert_width Chrome 4.0.249.89 70 0.0400 246 mass_insert Chrome 4.0.249.89 70 0.0400 327 mass_noinsert Chrome 4.0.249.89 88 0.0556 367 reuse_reinsert Chrome 4.0.249.89 88 0.0556 383 jquery Chrome 4.0.249.89 88 0.0556 863 full_reinsert Chrome 4.0.249.89 187 0.0000 105 jquery Chrome 5.0.307.11 187 0.8806 109 reuse_insert Chrome 5.0.307.11 123 0.0000 110 mass_insert_width Chrome 5.0.307.11 176 0.0000 231 mass_noinsert Chrome 5.0.307.11 176 0.0000 237 mass_insert Chrome 5.0.307.11 187 0.0000 314 reuse_reinsert Chrome 5.0.307.11 187 0.0000 372 full_reinsert Chrome 5.0.307.11 12 0.7500 82 reuse_insert Chrome 5.0.335.0 12 0.2500 102 jquery Chrome 5.0.335.0 [...] I want to modify this query to return only the browser/version/method with the lowest timing - i.e. something like: 88 0.8333 184 reuse_insert Chrome 4.0.249.89 187 0.0000 105 jquery Chrome 5.0.307.11 12 0.7500 82 reuse_insert Chrome 5.0.335.0 [...] How can I do this, while still returning the method that goes with that lowest timing? I could filter it app-side, but I'd rather do this in mysql since it'd work better with my caching.

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• ERROR 1005 (HY000): Can't create table 'tmp' (errno: 13)

  - by kobey

  Hi, I'm Running Mysql on ubuntu 9.10, the process of Mysql is running as root, I'm using root account when logging to Mysql, which I gave all privileges, I'm using my own db(not mysql), I can create a table, but when i try to create Temporary table i get this error: ERROR 1005 (HY000): Can't create table 'tmp' (errno: 13) For this query: CREATE TEMPORARY TABLE tmp (id int); I've plenty of space in my hard drive, all permissions are granted(also var/lib/mysql have mysql permissions). Any idea? Thanks, Koby

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• Exact matching of strings in SPARQL?

  - by Taz

  I have this query. It match anything which has "South in its Name". But I only want the one whose foaf:name exactly matches "South" SELECT Distinct ?TypeLabel Where { ?a foaf:name "South". ?a rdf:type ?Type. ?Type rdfs:label ?TypeLabel. }

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• MySQL & PHP Parameter 1 as Resource

  - by Nik

  Alright, PHP is throwing this error at me (in the log) when I run the code mentioned below: Error mysql_num_rows() expects parameter 1 to be resource, string given in (place) on line 10 Line 9-11 $queryFP = ("SELECT * FROM db"); $countFP = mysql_num_rows($queryFP); $aID = rand(1, $countFP); I think it has something to do with the $queryFP's syntax, but I'm not completely sure how to fix it since $queryFP's syntax is the simplest query I've ever seen.

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• How to use CASE in SQL , Syntax Error being shown

  - by Shantanu Gupta

  I am trying to retrieve some records from table based on my query but it shows me an error Msg 102, Level 15, State 1, Line 2 Incorrect syntax near ' select vd.LedgerId,(CreditAmt-DebitAmt) AS NET, CASE NET WHEN NET > 0 THEN 'Debit' WHEN NET < 0 THEN 'Credit' ELSE 'Nil'End from dbo.vdebit vd INNER JOIN dbo.vCredit vc ON vd.LedgerId=vc.LedgerId

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• FitNesse/Slim String Operators

  - by grootjans

  Is it possible to express this in a Query Table in FitNesse with SLIM for .net: contains(data) startswith(data) endswith(data) I know from a previous question it was possible for FitNesse/Fit with cell handler loader. I'm looking for the equivalent in Slim.

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• fast retrieval from MYSQL DB

  - by trojanwarrior3000

  I have a table of users - It contains around millions of rows (user-id is the primary key). I just want to retrieve user-id and their joining date. using "select user-id,joining date from table user" requires lot of time.Is there a fast way to query/retrieve the same data from this table?

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• Sql Shorthand For Dates

  - by vigilant

  Is there a way to write a query equivalent to select * from log_table where dt >= 'nov-27-2009' and dt < 'nov-28-2009'; but where you could specify only 1 date and say you want the results for that entire day until the next one. I'm just making this up, but something of the form: select * from log_table where dt = 'nov-27-2009':+1;

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• mysql PDO how to bind LIKE

  - by dmontain

  In this query select wrd from tablename WHERE wrd LIKE '$partial%' I'm trying to bind the variable '$partial%' with PDO. Not sure how this works with the % at the end. Would it be select wrd from tablename WHERE wrd LIKE ':partial%' where :partial is bound to $partial="somet" or would it be select wrd from tablename WHERE wrd LIKE ':partial' where :partial is bound to $partial="somet%" or would it be something entirely different?

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• Why better isolation level means better performance in MS SQL Server

  - by Oleg Zhylin

  When measuring performance on my query I came up with a dependency between isolation level and elapsed time that was surprising to me READUNCOMMITTED - 409024 READCOMMITTED - 368021 REPEATABLEREAD - 358019 SERIALIZABLE - 348019 Left column is table hint, and the right column is elapsed time in microseconds (sys.dm_exec_query_stats.total_elapsed_time). Why better isolation level gives better performance? This is a development machine and no concurrency whatsoever happens. I would expect READUNCOMMITTED to be the fasted due to less locking overhead.

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• Deferring frequent updates in MySQL

  - by cdecker

  I have frequent updates to a user table that simply sets the last seen time of a user, and I was wondering whether there is a simple way to defer them and group them into a single query after a short timeout (5 minutes or so). This would reduce queries on my user database quite a lot.

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• Select random row from MySQL (with probability)

  - by James Simpson

  I have a MySQL table that has a row called cur_odds which is a percent number with the percent probability that that row will get selected. How do I make a query that will actually select the rows in approximately that frequency when you run through 100 queries for example? I tried the following, but a row that has a probability of 0.35 ends up getting selected around 60-70% of the time. SELECT * FROM table ORDER BY RAND()*cur_odds DESC

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