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

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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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60 views

Why are correlated subqueries sometimes faster than joins in Postgres?

This relates to the dataset described in Postgres is performing sequential scan instead of index scan I've started working on adapting the import logic to work with a more normalised schema – no ...
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1answer
183 views

How to select from 3 tables while using count on 1, and sum on another?

I'm stuck on this one query. Here is my setup: table 1 (shows) show_user show_count table 2 (views) view_user view_views table 3 (users) user user_name What I need to is produce results ...
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PostgreSQL seems to create inefficient plans in simple conditional joins

Consider these two queries: SELECT t1.id, * FROM t1 INNER JOIN t2 ON t1.id = t2.id where t1.id > -9223372036513411363; And: SELECT t1.id, * FROM t1 INNER JOIN t2 ON ...
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2answers
276 views

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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How to combine UNION and INNER JOIN?

I'm fetching the grandparent of all nodes in a tree as follows: SELECT P.id, P.parent, GP.parent gp_id FROM product_groups P INNER JOIN product_groups GP ON P.parent = GP.id There is ...
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46 views

MySQL query too long to execute

I have one query that work pretty well: SELECT [MANY THINGS] FROM vehicule v0_ FORCE INDEX (PRIMARY) INNER JOIN categorie_vehicule c1_ ON v0_.idCategorieVehicule = c1_.idCategorieVehicule INNER ...
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PostgreSQL - Simple column binding

I have many tables of the same length (number of rows) that were previously ordered by some columns as they were being written on disk. My SELECT is of the form: SELECT t1.id, t1.value, t2.value, ...
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13 views

aggregate on join latest value

This is a problem I often get stuck in and I hope there is a solution. Let's build an example: Table products: product_id, product_name Table Prices: product_id, valid_since, Price Lets say I ...
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531 views

Mysql improve Self join performance large table?

I have a task to help identify conflicting IP ranges , I want to highlight when one companies IP range falls within another's ... below is the sample table, I have converted the IP ranges from .dot ...
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1answer
307 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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1answer
46 views

INNER JOIN for 3 tables [duplicate]

I am doing a small course in SQL during my academic degree, I am very new with this material. I saw Inner joinning 3 tables on StackOverflow, I tried to do INNER JOIN between my three tables, the ...
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40 views

Left Join Not returning rows when date is in range of longer than 1 day

How do I left join Table A and B? SELECT dev_hour.hour,rtdogs.delivery_date,rtdogs.delivery_hour,rtdogs.total_offer FROM ( SELECT hour FROM ( SELECT * FROM delivery_hour ) xx ...
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2answers
50 views

Most Recent order from multi join query

Here's the CTE version of the query, but it is returning multiple rows for the same customer. Not just the row containing the most recent open order date: with LatestOPenOrderDate_CTE AS ( Select ...
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127 views

Remove duplicates from multiple joins

I'm using WordPress $wpdb->get_results for this query (it is simplified for question purposes): SELECT customer.id, customer.name, address.address appt.appointment_date, pay.date FROM customers ...
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59 views

Return 2 columns from MySQL subquery?

I'm new in MySQL programing and I have one problem. I created this query: SELECT *, topics.createdate AS TopicCreateDate, (SELECT (SELECT username FROM users ...
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1answer
61 views

Subquery can't find column from superquery's join

I'm running into some trouble with SQL: Basically I'm trying to get a result set back that contains a sum of ALL questions asked to employees (grouped by company) and also add the "onetime_items" ...
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1answer
34 views

Joining 4 tables of which one is unrelated

I have 4 tables as follows. I want to find a wholesum resultset, limited to 25 records, in the following way: Users from Table1 based on a condition And those Users should not be in Table2 [Non ...
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1answer
620 views

How to improve the performance of SELECT queries with multiple JOINs on a 50GB database hosted on AWS m3.medium MySQL RDS?

Example query: SELECT p.ListAgentEmail, p.ListAgentFirstName, p.ListAgentLastName, p.ListingKey FROM Property_RES AS p INNER JOIN Property_RES_COUNTIES_OR_REGIONS ON ...
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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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1answer
112 views

Hash Join vs Hash Semi Join

PostgreSQL 9.2 I'm trying to understand the difference between Hash Semi Join and just Hash Join. Here're two queries: I EXPLAIN ANALYZE SELECT * FROM orders WHERE customerid IN (SELECT customerid ...
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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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1answer
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Combining GROUP BY and JOIN

This seems like a really simple request, but I can't find the answer. I'll admit that I only have a very limited understanding of JOINs, so it could just be that I just don't fully understand the ...
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1answer
51 views

Postgresql join removal

I just watched the very interesting video from Rob Farley "Designing for simplification" and I was wondering if the 4 rules given in the video for join removal also hold on PostgreSQL. If a view is ...
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43 views

MySQL FULL JOIN on same table

I have a table like this: And I want to get something like: fecha siguiendo seguidores 2016-01-02 430 1430 2016-01-03 450 NULL 2016-01-04 NULL 5000 ...
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Natural join question, I have the answer, but I don't know why it's correct. Help?

So I have a relatively simple database schema. I'm not sure why the where clause in the answer magically makes the dept_name duplication problem go away. I'm new to all this and I'm sure the ...
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1answer
54 views

How do I join information schema to the table's data?

I need to join a table using it's column name from the INFORMATION SCHEMA. Is this possible? I actually found another way to work around it. I am using Innodb. For the structure it's kind of ...
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1answer
39 views

Join table into different columns

I have two tables (simplified). table1: - id (serial) table2: - table1_id (integer) - value (text) - type (integer) I want to join these two tables, but depending on the type, I want ...
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60 views

Perform join on multiple tables

I have three tables right now in a postgres DB: Artists ID Name Shows ID Date Venue Price Is_sold Ages Time Multi_day Pit Artists_shows ID Show_id ...
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2answers
38 views

Get rows with minimum value

I have tables company: company_id | - - - - - - - - - - - - - - 1 | 2 | employee: employee_id | - - - - - - - - - - - - 1 ...
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3answers
64 views

Union Query format in mysql

I am training in MySQL. I have database called ships. My goal is => For each class, define the number of ships of this class that were sunk in battles. Result set: class, number of sunked ships. Here ...
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63 views

NOT IN (together with join) query

I have two tables : Part, OrderLine: Part (PartNum PK, PartDesc, Price) OrderLine (OrderNum PK, PartNum PK, QtyOrdered) And I want to find out the parts that were not ordered. I think I have a ...
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72 views

How to optimise multiple joins with OR?

I need to extract some statistical information form drupal database tables. The problem with drupal is that it splits it's data for entities across multiple tables and getting simple information from ...
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2answers
78 views

Multiple WHERE conditions on same column =val1 but doesnt=val2 or val3

I am trying to filter a table which has NON-UNIQUE transaction id's, joined to a products table on 1 common column. The filter needs to be as follows: equal to :group1 AND NOT equal to :group2 AND ...
2
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1answer
51 views

Inner Joins between Subsets of the Same Table

All, I am trying to figure out the syntax for doing joins between subsets of the same table. I have: Employee ( EmpId PK , EmpFirst, EmpLast, EmpMid, DateHired, SSN, DateBirth, Gender, PhoneNum, ...
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1answer
73 views

Select another row if NULL

In a MySQL database I have these tables: Table 1: News news_id int (PK) category int (FK) rating tinyint Table 2: News Detail news_detail_id int (PK) news_id int (FK) language_code char ...
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JOIN on 3 tables being slow

everyone. Can't figure out what indices are missing or how to rephrase my query. I created about a milllion of test entries in each table to see performance. Query takes about 1.5 seconds which is ...
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Can we do a Join on SQL tables on M:N relationship?

hope this is not too dumb/simple. I have been practicing joins recently and I have never seen a join done between tables T1, T2 that are in an M:N (Many-Many) relationship. Instead, joins are made ...
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1answer
54 views

Selecting Only One Record with Most Recent Date Using Table Join

I have a list of 463 CARRIER_CD. I am attempting to retrieve the most current BILL_DT for each of the 463 CARRIER_CD. I have uploaded the 463 unique CARRIER_CD to a database named edw_sbx_bt the ...
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2answers
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Using SELECT in the WHERE clause of another SELECT

I have made a draft remote application on top of libpq for PostrgreSQL. It behaves well, but I have profiled the general functioning of the application. For each final business result that I produce, ...
2
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1answer
64 views

Join query returning 0 rows - impossible where

My query is performed from a php web request using a PDO prepared statement. My desired output is to list the top 10 brands which have the same transaction id as the 'selected' brand :brand by order ...
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I have following two MySQL queries and i want to execute it inside one procedure

Following query returns 10 rows of recipe id's i wants to pass first query's output which is of 10 rows to the second query and display the output of both the queries inside a procedure. Query 1: ...
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SQL queries to only show most recent purchase records for individual food items

I'm working with a food purchasing / invoice system in MS Access 2013 and am trying to create an SQL query that will return the most recent purchase price for each individual food item. Here is a ...
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2answers
37 views

How do I write this cross Join in MySQL?

It should create a set of columns (ControlRange, SensorBias, SensorError, VDCurve, INSHalfCurve, INSSensCurve, ExogDEXCurve, InitGlucose) and all permutations of their values. I want the order given ...
3
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1answer
165 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
71 views

MySQL very long-running queries

I have a quite large db (800+Mb dump file) that I imported to my local server. It's a Wordpress db from witch I need to extract certain posts. There are around 160,000 posts inside. Currently I'm ...
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Join on multiple columns with OR

I have a table of 1 million record to join another table with 100000 records. However, there are 5 potential keys (lets assume Account Number, email address, membership number, alternative email, and ...
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1answer
36 views

UNION or SELF JOIN?

I have a table to hold parent and child posts together. +------+----------------+--------------+-------------+------------+ | p_id | parent_post_id | child_status | post_status | post_title | ...
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1k views

Joining multiple tables results in duplicate rows

I am running SQL 2005. I am getting more rows then I expect returned by my query. I believe it has something to do with my join statements. Here is my query: There are multiple tables that have ...