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

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Handle a Search on 2 Big Tables

Hello i want to realize a exchange system with 2 tables. 1 Table for "the user is looking for" 1 Table for "the user has to share" the Tables are very simple id bigint user_id bigint object_id ...
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90 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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MYSQL Tables Join Filtering For Favorites

I am in need of some help figuring out the best way to join separate tables I am using. I am essentially trying to output a list of schools (first table in MYSQL) where one column is an empty star ...
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1k views

Select multiple columns in subquery

I am having trouble selecting all columns in a sub query and can't seem to get anywhere with joining for replacement. My Table Data is: CREATE TABLE `w7nwd_com_mtapp_product_engine` ( `id` ...
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1answer
29 views

Joining a column from another table with InnoDB engine

I'm using MySQL with InnoDB and I want to join the location column from products table into a productStock table. I have this table 'products' mysql> select * from products; ...
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1answer
169 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
72 views

Speed up a MySQL BETWEEN query

SELECT dateToFind FROM table1 INNER JOIN table2 ON dateToFind BETWEEN dateFrom AND dateTo I need to improve the performance of this kind of query. I added BTREE indexes on dateToFind, dateFrom, ...
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2answers
20 views

Subquery or multiple left joins, or both?

I have two tables, for simplicity table1, with id as Primary key, and a field name, and table2 with the same. Each table has quite a few records, but during a complicated form process, the user is ...
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2answers
33 views

Combine two queries from 1 table, 1 to Many

I have the following queries select o.increment_id, o.customer_id, round(o.base_grand_total * o.base_to_global_rate,2) as revGBP, DATE_FORMAT(o.created_at, '01/%m/%Y') as 'MonthofOrder', from ...
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3answers
117 views

Alternatives for a LEFT OUTER JOIN query

Problem I have a SQL statement with an LEFT OUTER JOIN which works fine on our Microsoft SQL Server. My problem is that i have to be compatible with H2 Database and this one got a bug with OUTER ...
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1answer
23 views

How to optimize a very slow query with joins and group by?

I have this GTFS database : All the ***_id columns are indexed, and there are foreign keys between tables (such as a FK on trips.route_id to routes.route_id). So basically the link between a stop ...
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How to use join with this query? [closed]

This query is working fine, and giving the right result. In this query all columns are in one table, but now I have made some changes. Now columns named Semester and Major are in different Table ...
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130 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
37 views

SELECT count vs DELETE JOIN. Why/how are they different?

Can someone explain in what way these queries could be different and the results are not the same? > begin; Query OK, 0 rows affected (0.01 sec) >select count(*) from tableA a JOIN tableB ...
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11 views

How to join 2 tables and traverse up hierarchy at the same time

Any help that can be given on a current problem I'm having in an Oracle environment would be greatly appreciated. I have 2 tables. One contains jobs to be performed on pieces of equipment, the other ...
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1answer
104 views

CROSS APPLY versus INNER JOIN

I was reading a lot about CROSS APPLY versus INNER JOIN recently. I tried writing some queries and they both work in a similar fashion, the execution plan seems to be same as well. Maybe someone ...
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29 views

Selecting most recent date when dates are stored in another table

Working in a MySQL database, I have tables set up like this: Table song_instances has song_id (int), meeting_instance_id (int) The meeting_instances table has columns meeting_instance_id (int), ...
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2answers
123 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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34 views

How are derived table implemented in MySQL

When MySQL makes a derived table as a result of SELECT (SELECT ...) etc or SELECT * FROM a JOIN (SELECT * from B) etc or SELECT * FROM (SELECT ...) Are these derived temporary tables created ...
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Packet and N-SubPacket Msql query ( same as catgeory and N sub catgeory )

First of i am PHP Developer , and working on huge project alone .i think i have made many mistake in creating table. and below is one of those. I am making packet type system when in my Packet Table ...
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1answer
163 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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1answer
188 views

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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49 views

How to JOIN more than two tables?

Following is the schema of my Tables: Marks_Table (SubjectCode,TypeID,MarksObtd) Subjects_Table (SubjectCode, Subject) Types_Table (TypeID, Type) I want to Select the Marks_Table table with ...
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23 views

Drastic change in query speed when changing from Oracle 9i to ANSI outer join syntax

I am working on simplifying a query originally written for Oracle 9i. In the process I changed the join syntax from the Oracle 9i syntax to ANSI. The names of the tables and columns have been changed ...
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2answers
45 views

mysql join not working as expected

i want to select schedule of specific teacher for a given day .... statement should assume that a teacher may teach in elementary and high school here is my statement `select class.name as ...
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1answer
104 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
43 views

How can I optimize this Cross Table COUNT() mysql query?

I am trying to cut down the retrieval speed of this MySQL query. All instances of COUNT() point to the PRIMARY key of each field. Currently this query makes my MySQL hang. It seems ridiculous as I'm ...
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62 views

Select all rows with multiple conditions in another table

Here is my simplified database scheme -- ----------------------------------------------------- -- Table `products` -- ----------------------------------------------------- CREATE TABLE IF NOT EXISTS ...
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1answer
25 views

SQLITE table joining with group

MESSAGE TABLE USERS msg_id | msg_to | msg_from | msg_body | msg_date user_id | user_name 1 1 2 hi 22/1/14 ...
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1answer
133 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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2answers
85 views

JOIN on variable number of columns

I have the two tables courses AND something_about_courses: courses course_code course_session course_type something_about_courses course_code course_session some_description To ensure that I ...
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1answer
398 views

Join tables in two databases make query slow? is better to partition db?

I have a table1 in db1 and table2 in db2 on SQL Server 2008 R2. If I make a select query joining both tables, it's really slow to get the results. A simple query like SELECT * FROM db1.dbo.table1 ...
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51 views

Pivoting some row data into columns (SQL Server 2008 R2)

Sorry if this has been answered before but I'm exhausted and on a time line. Maybe I'm just an idiot. I'm designing a data export from One application to import into another. Full-Disclosure: I did ...
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68 views

queries for hierarchical data

This table is a questions and answers CMS and i want to know how data is fetched from these tables. +------+----------+-------+ | id | parentid | type | +------+----------+-------+ | 1 | 0 ...
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1answer
44 views

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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100 views

Outer Apply vs Left Join Performance

I am Using SQL SERVER 2008 R2 I just came across APPLY in SQL and loved how it solves query problems for so many cases, Many of the tables I was using 2 left join to get the result, I was able to ...
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2answers
5k views

How to JOIN two table to get missing rows in the second table

In a simple voting system as CREATE TABLE elections ( election_id int(11) NOT NULL AUTO_INCREMENT, title varchar(255), CREATE TABLE votes ( election_id int(11), user_id int(11), FOREIGN KEYs for ...
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2answers
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“All joins can be rewritten to sub queries”, is this statement true?

I wonder if there any case that a join can not be converted to a sub-query. BTW: I am not discussing advantages and disadvantage of using sub-query or using join.
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1answer
77 views

SQL SELECT - adding field to SELECT with JOIN is changing the results

I have a SQL sentence with JOIN, running on mysql 5.5.16: SELECT DISTINCT (ot.orders_id), ot.value FROM orders_status_history osh INNER JOIN orders_total ot ON ( osh.orders_id = ot.orders_id ) WHERE ...
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4answers
5k views

Recursive self joins

I have a comments table, which can be simplified down to this: comments ======= id user_id text parent_id where parent_id is nullable, but might be a key for its parent comment. Now, how can I ...
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2answers
56 views

left join not working [closed]

CREATE TABLE `table1` ( `id` INT(10) NOT NULL ) ENGINE=InnoDB; CREATE TABLE `table2` ( `id` INT(10) NOT NULL, `value` INT(10) NOT NULL ) ENGINE=InnoDB; INSERT INTO table1 VALUES (1), (2), (3), (4); ...
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1answer
37 views

Joins in Update statement in sqlite

CREATE TABLE Table_1 ( Id INTEGER PRIMARY KEY AUTOINCREMENT NOT NULL , EmailId VARCHAR ) INSERT INTO Table_1 VALUES (1,'raj@gmail.com'); INSERT INTO Table_1 VALUES (3,'test@gmail.com'); ...
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1answer
20 views

PostgreSQL SQL syntax - JOIN and substrings

I have a single table of hostnames and NFS exports, some but not all of which are related. Example entries: HOST VOLUME ----- ---------- host1 vol1 host1 vol2 host1 ...
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28 views

Minimize table joins in design

Probably didn't come up with the best title, but I'll explain what I'm trying to do. I need to be able to track gym members, trainers, workouts, and gym locations. I've created a simple example below. ...
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1answer
16 views

MySQL Join, Force NULL Row

I'm having a bit of trouble figuring out how to do this -- I need to select all rows from table t1, join table t2 -- but include a null row from t2 for each record in t1 (even if rows match in t2). ...
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2answers
25 views

MySQL get values from the other table by using inner joins

In mysql I have 3 tables called as ps_product_lang ps_order_detail and ps_image here are the tables sample data === ps_product_lang === CREATE TABLE IF NOT EXISTS `ps_product_lang` ( ...
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103 views

SQL Server Multiple JOINS with Table Value Function - query never ends

I have a query with 4 joins using a table value function to get the data and when I execute it the query never ends. Issue Details Table valued function: CREATE FUNCTION [dbo].[GetIndicator] ( ...
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1answer
3k views

Subqueries run very fast individually, but when joined are very slow

ypercube solved the problem. Subqueries were totally unnecessary, and the whole thing works with plain joins. It is still strange that MySQL's optimizer could not make use of my original query, ...
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1answer
37 views

Query Rows That Have a Following Row That Meets Criteria

Will try to do my best to explain this, as I don't really know how to word this to search for an answer. I'm a constantly learning but still newish SQL user who thus far has been able to solve most ...
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1answer
81 views

If an INNER JOIN in a query returns no rows, do additional INNER JOINS add a significant performance overhead?

If I make a query as follows: SELECT * FROM TableA A INNER JOIN TableB B ON A.AID = B.AID INNER JOIN TableC C ON B.BID = C.BID Does the INNER JOIN with TableC add significantly to the performance ...