query-optimization

问题 The following code removes records of tasks related to inactive projects from the table. delete from [Deliverables] where [Deliverables].[ProjectID] not in ( select [ProjectID] from [ActiveProjects] ) I've read somewhere that using NOT IN with subquery that returns a lot of values is not really the most efficient thing to do and it's better to use EXCEPT clause. However, when I try to use the following code, I get an error (Incorrect syntax near the keyword 'except'.) delete from

问题 I have 3 products A, B, C Then I have 2 addons for those products, : 1, 2 Then I have table of price ranges vs quantity ranges. See below PRODUCT vs QUANTITY PRICES +---------------+--------+----------+ | Product | Qty | Price | +---------------+--------+----------+ | A | 0-10 | $2 | | A | 10-20 | $1 | +---------------+--------+----------+ | B | 0-10 | $3 | | B | 10-20 | $2 | +---------------+--------+----------+ | C | 0-10 | $4 | | C | 10-20 | $3 | +---------------+--------+----------+

问题 I realise different solutions will have different variations of what "Working Days" means but in my case I mean Monday to Friday inclusive. Basically I have Created a function to do the calculation for me and my current solution works. My concern (and reason for asking this question) is that I am worried that this is a bad way of achieving this because the function is being called with a very high frequency. In the last 3 months it has been called 12 million times on a production system, with

问题 Server version: [root@cat best]# /usr/libexec/mysqld --version /usr/libexec/mysqld Ver 5.1.47 for redhat-linux-gnu on i386 (Source distribution) Schema: CREATE TABLE `Log` ( `EntryId` INT UNSIGNED NOT NULL AUTO_INCREMENT, `EntryTime` TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP(), `Severity` ENUM( 'LOG_LEVEL_CRITICAL', 'LOG_LEVEL_ERROR', 'LOG_LEVEL_WARNING', 'LOG_LEVEL_NOTICE', 'LOG_LEVEL_INFO', 'LOG_LEVEL_DEBUG' ) NOT NULL, `User` TEXT, `Text` TEXT NOT NULL, PRIMARY KEY(`EntryId`), KEY

问题 I run the following query on my database : SELECT e.id_dernier_fichier FROM Enfants e JOIN FichiersEnfants f ON e.id_dernier_fichier = f.id_fichier_enfant And the query runs fine. If I modifiy the query like this : SELECT e.codega FROM Enfants e JOIN FichiersEnfants f ON e.id_dernier_fichier = f.id_fichier_enfant The query becomes very slow ! The problem is I want to select many columns in table e and f, and the query can take up to 1 minute ! I tried different modifications but nothing works

问题 I have the following huge query that contains repeated subqueries , It looks really inefficient to me. How can i optimize it ? SELECT T2.date1, T2.date2, T2.period, T1.market, T1.ticker, 0 AS scenario FROM (SELECT DISTINCT Q.market AS market, Q.ticker AS ticker FROM portfolio.scenario S RIGHT JOIN portfolio.quote Q ON S.series = (SELECT S.series FROM scenario S WHERE S.date1 >= '2009-09-01' AND S.date2 <= '2010-07-01' AND S.period = 'QUARTER' ORDER BY S.date2 LIMIT 1) AND Q.market = S.market

问题 I have a large table with millions of records. Table `price` ------------ id product site value The table is brand new, and there are no indexes created. I then issued a request for new index creation with the following query: CREATE INDEX ix_price_site_product_value_id ON price (site, product, value, id); This took long long time, last time I was checking ran for 5000+ seconds, because of the machine. I am wondering if I issue another index creation, will it use the existing index in the

问题 I need some help writing/optimizing a query to retrieve the latest version of each row by type and performing some calculations depending on the type. I think would be best if I illustrate it with an example. Given the following dataset: +-------+-------------------+---------------------+-------------+---------------------+--------+----------+ | id | event_type | event_timestamp | message_id | sent_at | status | rate | +-------+-------------------+---------------------+-------------+---------

问题 The following query takes mysql to execute almost 7 times longer than implementing the same using two separate queries, and avoiding OR on the WHERE statement. I prefer using a single query as I can sort and group everything. Here is the problematic query: EXPLAIN SELECT * FROM `posts` LEFT JOIN `teams_users` ON (teams_users.team_id=posts.team_id AND teams_users.user_id='7135') WHERE (teams_users.status='1' OR posts.user_id='7135'); Result: id select_type table type possible_keys key key_len

问题 credit table and validtransaction table have million record data from year 2008 onwards. We are doing a migration. So I need to find out the credittypeids which are no longer in use after 2017 (periodseq=1055), so that these need not be migrated. This is the query and the >= part is resulting in huge cost. Please suggest an alternative. SELECT CREDITTYPEID FROM CREDITTYPE ct WHERE NOT EXISTS (SELECT 1 FROM CREDIT C WHERE C.PERIODSEQ>=1055 AND C.CREDITTYPEID=CT.CREDITTYPEID ); 回答1: The