An SQL join clause combines records from two or more tables or views.

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MYSQL joining 3 tables with left join

I have these tables: pupils: (id_pupil, name, surname, email, user, pass, level, class) incidents: (id_incidents, date, time, type_incident, comments, id_pupil, id_user, subject, id_trimester) ...
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Postgresql subquery speed much slower than individual queries

In Postgres 9.1. I am attempting to do a single query to get the timezone of a given postal code. I have data loaded in my database, and I am using PostGIS to store the coordinates of each postal ...
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61 views

MySQL: NOT EXISTS vs LEFT OUTER JOIN…IS NULL

Is NOT EXISTS or LEFT OUTER JOIN...IS NULL more efficient for finding records in one table that aren't in another? Specifically, I'm trying to figure out which of the two queries below is better: ...
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82 views

Joining on a field with different values

I am trying to join data from two completely different sources. One source contains an employee's schedule information, and the other tracks what they actually worked (like what time they actually ...
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1answer
90 views

Minimizing Page Fetches

I have a complicated database structure and am trying to use it to retrieve Records based on multiple selection criteria from several tables. As a general rule, is it better to attempt to use ...
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1answer
35 views

Get the value of one attribute from the reference key of another table?

I have two tables named as ps_order_detail and ps_product_lang in MySQL. I want to get the product name from one table whose reference key is in another table. I have two tables. First the ...
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Does MySQL load the entire row into memory, or just the columns used in WHERE, ORDER BY and GROUP BY?

I have a table that isn't very large row wise (in the 100ks range), but that contains a lot of raw data that is very large in size. Despite having a relatively little number of rows, it's around ...
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104 views

Data Analysis with MongoDB or MySQL

I have a need for processing some data in order to come up with some statistic. This is the scenario: Each user can answer several questions from the question list. They pick their answers from a ...
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120 views

Optimizing multiple MySQL sub-queries and joins for multiple runs

The query (below) that's running is taking ~0.6 sec which normally would be fine but it gets run almost 1300 times for different custids. How can I make it run faster? Setup: Mac OS X 10.7.5 MySQL ...
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Efficient way to write query for multiple table which depends on column value of a table in mysql?

In the given schema, there is a table A having column A1,A2,A3,A4 There are three more tables i.e. B,C,D If the value in A4 is b, i have to lookup table B. If the value in A4 is c, i have to lookup ...
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SELECT, PROJECT, CARTESIAN PRODUCT and JOIN

I have the following tables; DOG +----------------------------------------------+ | Name Type Age Kennel_name Owner_name | +----------------------------------------------+ ...
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join performance, index vs. index+foreignkey

I'm using an orm framework that handles data (and its integrity) on top of mysql. So far I ignored foreign keys because the orm handles that just fine. I recently read that foreign keys can enhance ...
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Relation between lossy decomposition and Natural join?

I am confused with the lossy decomposition and natural join. Natural join(with common attribute): only respective common attribute for the resultant table is formed. Lossy: Natural join on tables ...
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104 views

MySQL join query indexes

After recently discovering the MySQL feature to log queries that aren't using indexes, I've been chasing these down in a large app, looking for places to improve performance. There is at least one ...
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69 views

How to index for a group by with columns from different tables?

Is it possible to create an index from columns of 2 different tables? If not, how do we optimize a query that does a group by on columns of 2 different tables? For example: the following ...
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Can't get rid of filesort on joined query sorting on second table

For some reason, this query: EXPLAIN SELECT * FROM biz as b INNER JOIN listings as l ON b.id = l.biz_id WHERE l.pub_id = 14 AND b.cat_id=310 ORDER BY l.level DESC, l.random DESC LIMIT 5; says it ...
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parenthetic grouping of join clauses

What is the difference between these joins? a left join b left join c (a left join b) left join c a left join (b left join c) Does the grouping only affect the order of the joins? Will the query ...
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How can I join one to one to (many to one) without using group_concat

I have a table structure as follows: -- -- Table structure for table `emails` -- CREATE TABLE IF NOT EXISTS `emails` ( `ID` int(5) NOT NULL AUTO_INCREMENT, `email` varchar(255) COLLATE ...
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multiple child records in a single row by join

I have one master table (teacher) structured like teacherId Name Class 1 Praveen 10 2 John 9 and having a child table (student) structured like studentId ...
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156 views

Multi-Table Join to Single Destination

I am having a serious performance issue with join together four tables and placing the results (in a certain permutation) into one destination table. I am using MSSQL 2008 and good ole T-SQL. To ...
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Selecting posts, user details and votes from 3 SQL tables

I have a user table with id, username, email etc.. post table with id, uid (user id), content etc and vote table with id, uid, pid (post id), vote (ENUM : '1' and '-1'). In the vote column of Vote ...
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35 views

USING to join multiple tables with same field

I have 4 tables, each with a common field QuestionnaireId. I am wondering if there is any difference in output or performance difference between using USING on the field in each join or by specifying ...
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MySQL - query join returning zero recs from table with data

I've provided a file that has the table structure and some sample data that I'm working with. I don't understand why I'm getting nulls from a joined table, where there is data. Here's my query ...
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Equivalent of old style join with new style

Can someone please help me write the following join expression in new style: Select tb1.col1,tb2.col2 from table1 tb1, table2 tb2 where tb1.col1>=tb2.col2 I know that the equivalent of ...
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Alternatives for subquery

There are three tables: product_hits, products, and product_subcategory_map. I want to count the number of product_hits and for each product. There could be more than one subcategory in the ...
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Select Foo object without any specific Bar events

Consider two tables: Foo: id INT, name VARCHAR Bar: id INT, foo_id INT REFERENCES Foo(id), event_type VARCHAR DEFAULT NULL, event_duration INT DEFAULT NULL Each Foo item can have ...
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Alternative to TEMPORARY tables capable of re-opening in a query?

I use TEMPORARY table for calculation of temporary data, but TEMPORARY tables in mysql has a big limitation, which made it useless for me. A table cannot be re-opened in a query. This mean I cannot ...
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Better way to query for object with multi level parts

For example, an object consists of several parts, and each part consists of several sub-parts, and so on. In MySQL, it looks like this: table `object` ----------------------- object_id, object_name ...
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MySql INNER JOIN doesn't use composite index

I have two tables, table A which contains date and name of table B entry and table B which contains its name and type. Table a has a composite index on table_b_name and date. I'm selecting all table A ...
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130 views

How to increase MySQL performance with joins

I have a MySQL database with InnoDB engine. Particularly one of my queries became very slow. The query is shown below: SELECT t1.`ARTREF1` FROM `lijnen` AS t3 INNER JOIN (`kortingen` AS t2, ...
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127 views

Missing values in INNER JOIN MS-Access?

When I run the following query in MS-Access: SELECT a1.ConStateNumber, a2.ConStateNumber FROM qryW2_yr_sum_slash_qryW2_q4_sum_result a1 INNER JOIN qryW2_q3_sum a2 ON a1.ConStateNumber = ...
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one vs two column index difference when doing JOIN query?

Let`s suppose that alfa,beta and gamma contains milions of rows so we need to create indexes obviously to get optimal performace for this query : SELECT * FROM alfa JOIN beta on beta.id = ...
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How Can I do and INNER JOIN USING (2 columns)?

Suppose we have: CREATE TABLE cscart_products_prices_temp LIKE cscart_products_prices; ALTER TABLE `cscart_products_prices_temp` DROP `percentage_discount`, DROP `lower_limit`, LOAD DATA LOCAL ...