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

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Performance inner join vs left join involving parallelism

I have a query which takes about 8 hours to finish. Simplified, the query looks something like this: SELECT [Some attributes, inconsequential] FROM RBM.Financial_Events RFE INNER JOIN ...
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24 views

How to avoid row locks on both tables joined in an update?

I have little knowledge about MySQL internals, but I'm experiencing that in a query like: UPDATE t1 JOIN t2 ON t1.id = t2.id SET t1.a = x, t1.b = y, [, ...] WHERE [ ... ] rows from both t1 and ...
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17 views

Join integration query involving multiple associations

I'd like some assistance in fixing this query. Let me explain the background on what it currently does, and then what I need to integrate. First, here are my current tables. users (performers) table ...
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31 views

Query optimization - contact should be extracted at most once for a particular customer

I have created a database for a telemarketing company Scenario is, the telemarketing company is selling contacts to the customers. Customers log on to the website and search for the contacts for ...
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228 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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27 views

Groupwise max then join

I have a votes table that has many subitems. I have a subitems action table that records what action was performed by which user on which group, on which subitem, on which vote Users can either ...
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39 views

Inner join on array columns from 3 tables

I have 2 tables that are related between them using integer data which is stored in arrays. Data table telemetria_data.historico_354677050164513 CREATE TABLE historico_354677050164513 ( imei ...
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40 views

Fetch items where related rows has different values

I have table in MySQL called attributes, and other table, attribute_values, one attribute can have multiple values, values identified by context attribute and has value_c attribute wich contain value. ...
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21 views

Why does SemiJoin node receive so bad statistic even after runnning ANALYZE

PosgtreSQL 9.4 I have two tables: CREATE TABLE home_transactions( id serial NOT NULL, transaction_id integer ); CREATE TABLE transactions( id serial NOT NULL, user_id, amount numeric(13,4) NOT NULL ...
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61 views

Whats the difference between the following queries? Getting the top 3 salaries for different department

I am practicing SQL and came across this issue. I am trying to find the top 3 salaries for each department. The table structure is basic with one employee table with columns ...
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54 views

How do I correctly group output from multiple tables?

I have more than 2 tables where entries are associated with dates. Each table can have multiple entries per date. I want to produce output that lists a date, then lists the entries of each table for ...
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47 views

3 tables joins performance issue

DB: Postgres 9.4 schema: table a: id, score table ab: a_id, b_id, b_type table b: id, name, type I am trying to get top 10 result in the following format: name, count(group by name), ...
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172 views

Update row value with a sub-select join

I am trying to update 1 column in all rows in a table to have an appropriate count value. Sadly, the SELECT query I am using won't let me join on a field in update table. The query looks like this ...
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46 views

Efficient structure for querying membership in many-to-many relationship where tableA has ONLY the indicated members from tableB?

I'm working on an application with a PostgreSQL back end. There is a many-to-many relationship between items in one table and tags in another table. The specs require that the application be able to ...
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38 views

Dealing with joins in persistent key-value stores

One promising emerging category of NoSQL databases is key-value stores. These include Redis (disk-backed), Riak, Aerospike and others. The problem I struggle with the most is the lack of joins. ...
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36 views

Type of relational/object-oriented database with improved joins for object graphs?

I would like to know if there is a specific name or term for the kind of database described below: I notice one of the biggest problems when working with relational databases and object trees/graphs ...
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45 views

Delete using join or using sub-query?

I need to delete rows from a table based on what is present in a temporary table. For me, both of these statements work : DELETE from main_table where `id` in (select `deletable_id` from ...
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405 views

Oracle 10.2.0.4 query hundreds times slower than the same query on Oracle 10.2.0.3

I have an issue with query on Oracle 11.2.0.4.0 (it takes forever to complete and CPU is at 100% all the time) so I was trying to change optimizer_features_enable to previous versions. It worked with ...
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992 views

How to display all the dates between multiple two dates in a table?

I want to display all the dates between two dates for a particular record And this is the table : ID Start_Date End_Date 1 2013-01-14 2013-01-18 2 2013-02-01 2013-02-04 and now i want to get all ...
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159 views

How to improve performance when joining against coalesce

In an effort to remove a caching layer from our application, I'm building a number of views to encapsulate the different ways a user can have access to a piece of content - one per "rule" of access. ...
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88 views

Poor performance filtering mysql spatial join

First of all, sorry for the crossposting. I ask this question in stackoverflow and they sent me here I have a mysql table with spatial references (GEOGRAPHIC_FILTER), like cities, countries, natural ...
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377 views

Limit relation one to many or one to one

In a relationship one to many or one to one you can limit the relationship of the related table? For example, I have a table 'cliente' and another 'acct', each 'cliente' can have thousands (perhaps ...
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121 views

Join and aggregate result and insert blanks for missing appendants

Consider these two simplified tables: CREATE TABLE "sources" ( "id" serial NOT NULL, "name" text NOT NULL, CONSTRAINT "sources_pkey" PRIMARY KEY ("id") ); CREATE TABLE "values" ( ...
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187 views

SELECT, PROJECT, CARTESIAN PRODUCT and JOIN

I have the following tables; DOG +----------------------------------------------+ | Name Type Age Kennel_name Owner_name | +----------------------------------------------+ ...
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791 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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173 views

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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219 views

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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162 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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508 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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103 views

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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45 views

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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1k views

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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886 views

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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40 views

Query the database for particular value in a column

I have 2 tables which look like this: Table_1: Contains Item Details ------------------------------------------------------ Item_ID | Location | Arrival_Date | Postage_Date | ... ...
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30 views

MySQL Update column with case on joined tables

I have 2 tables and I want to update table 1 using a case check on table 2: update cms.Clients c #c_id unique join cms.ClientDomains d #c_id not unique on c.c_id = d.c_id set c.country = case ...
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37 views

SQL Joining across multiple tables

I'm trying to query across multiple queries at once, it is fairly easy to run queries one after the other but that is not what I should be doing in this case. I have one free variable and the rest of ...
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26 views

Get records with specific group name from table A and see if any exist in table B, if it does then add matching records in Table B to group

Let me start off by saying I am not a DB admin or a DB pro, I work with SQL as a php developer but that's about it. So I hope I can explain this properly and I hope one of you DB guys/gals can help. ...
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24 views

How to use COUNT() properly with a 3 table join

I have a database where I have driver details, their assigned routes and their stop locations. For each driver on the database I need to find the location (or locations, as it could be more than one) ...
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12 views

Schema of equijoin in relational algebra

Why does equijoin return a schema consisting of all attributes from both relations (including intersection) when equality between them have already been established? That is, we know that for any ...
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57 views

Mysql FULLTEXT index not used in Many to Many table join search

I've got a set of data in the Books table, with BookID as the primary key. I've also got Subject and Location tables, each of which is joined to the primary Books table with a Many to Many table. ...
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23 views

Is it possible to stack similar columns from a subquery and join the other unique columns in one query?

I am fairly new to the sql world and have been struggling with a query. I have two subqueries that are generating tables with two columns. The first table is part # and model_countH. The second table ...
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30 views

Is it better to filter a small set of row with a BOOL or through a JOIN?

Let's say that I have a simple Books table: Books ----- id name description ... It's a pretty small table, at the moment with 60 records and it can grows, but slowly. On a webpage I want to show ...
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34 views

limit aggregate function across join

I have a facts table, and each fact has one-or-more distributors in fact_distributors. A distributor is an entity, and for reporting purposes entities are grouped together into an entity_group via ...
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26 views

How can I combine join and random choice from one table but 2 conditions?

I want to choose 200 entries randomly from a table However, I have two conditions the first 100 should be white and the other black. How can I join them? One possibility to do is to run following ...
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22 views

Joining one table with multiple tables for aggregate functions possible?

I am trying to get this seemingly simple looking query to work : SELECT c.id, c.name, count(chc.id) as contacts_count, count(cha.id) as addresses_count FROM (customers c LEFT JOIN ...
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8 views

Reason of poor performance of ANSI joins in Oracle 9i

Please before flagging as duplicate, read the last paragraphs. In an Oracle 9i database this query runs in 0.18 seconds: select count(*) from dba_synonyms s,dba_objects t where ...
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50 views

Update a field in table when a combination of three fields with a second table is matched

I have a database form an old archaeological project which I imported into a mysql DB. I have a table "graves" with 400+ entries: "graves" id necr burials single multi 1 1 1 ...
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93 views

Estimate the number of Tuples from relations

Quick question, and great help if possible: I have an exam tomorrow on a database module which I'm revising for, and one of the past papers had this question: Consider the following three relations: ...
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105 views

How to display additional column in select with true/false value [SOLVED]

Solved. Look in comment. I am using PostgreSQL 9.1. I have 3 tables: simcards: id serial NOT NULL, iccid character varying(30) NOT NULL, customer_id integer customer: id serial NOT NULL, name ...
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266 views

Performance hits with MySQL Left Joins and Order By

There are a lot of questions out there regarding this issue, but most answers seem to be very case-specific. I've tried to make this general so it'll help others too. The Issue We have a smallish ...