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

learn more… | top users | synonyms

4
votes
1answer
5k views

mySQL query optimisation — multiple joins or select … where not in (select distinct…)?

Background I have a Drupal install accessing a large users database (~200k rows) and my "People finder" functionality needs to access all those rows (in a random order). I don't seem to be able to ...
3
votes
2answers
7k views

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 ...
6
votes
3answers
4k views

Why is this Full Outer Join not working?

I've used Full Outer Joins before to get my desired results, but maybe I don't fully understand the concept because I am not able to accomplish what should be a simple join. I have 2 tables (which ...
3
votes
2answers
352 views

How do I calculate working business minutes?

I'm working on business inteligence reports and one of my task is to create reports for time tracking. I have to report on business minutes (10 hours per day) within business week (monday to ...
1
vote
1answer
71 views

How can this data be joined?

Definition: table_A table_B id,description id,description,id_table_A Column id_table_A is a foreign key to the primary key of table_A and is not mandatory. Sample data: ...
3
votes
1answer
4k views

Having trouble with Merge Join with SSIS

I am currently using Merge Join to perform an inner join on two sorted sets of data in SSIS. The problem I am having is that no records are being returned from the inner join. To troubleshoot I have ...
2
votes
1answer
405 views

Query takes hours

Up until now all queries in my PostgreSQL application were fast. During the last days, sometimes a query takes several hours. Index are healthy, because after dump, restore, vacuum -z, it is still the ...
2
votes
2answers
459 views

Joining based on date (or date range)

I'm not sure if I've completely fudged the design of my small hobby database (I'm not a DBA by any means), but I have a table like this (primary key is (staffid, effectivefrom)): staffid | target | ...
1
vote
1answer
583 views

Usefulness of Foreign Key WITHOUT reference option

Sorry, if this is naive question, but I searched a lot and did not get a vivid answers. Consider a simple InnoDB FOREIGN KEY without ON DELETE or ON UPDATE I think this will avoid INSERT of a value ...
2
votes
2answers
2k views

Limit WHERE to MAX() & COUNT()

This is my current mySQL query: SELECT e.*, MAX(m.datetime) AS unread_last, COUNT(m.id) AS unread FROM TAB_EVENT e LEFT JOIN TAB_MESSAGE m ON e.id=m.event_id WHERE ( m.`read` IS NULL OR ...
5
votes
2answers
552 views

Unexpected extremely long query time (~5 minutes using nested WHEN-INs)

For the first time, I am running up against a horrifically long execution time of a MySQL query (~5 minutes). The data in the database is highly (and not arbitrarily) normalized. It very efficient ...
2
votes
2answers
168 views

Validation of availability for a new order

I have a management application of sales, stock and payment on a warehouse whole saler from a web interface. In particular, when a order is effectuated it must create a line corresponding to each ...
2
votes
3answers
382 views

Express union which is dependent on other results

I would like to make a union of two tables that are actually in a hierarchical constellation. How would I write that in relational algebra? Say table A is the parent of B in a 1:n relationship. ...
0
votes
1answer
4k views

Oracle SQL for left outer join to rownum = 1 of another query?

Background I have a query joining many tables together, the chief of which is a workorder table. I also have a table called WOStatusHistory, which stores every status for every workorder. A diagram ...
6
votes
3answers
258 views

What does the output of a JOIN statement look like?

I've been wanting to use joins for a while, but I'm having trouble visualizing the output so I know how to put it to use. Let's say I have 2 tables: CREATE TABLE Cities ( id INT UNSIGNED PRIMARY ...
2
votes
2answers
1k views

Update column by comparing date and string values together

I have problem in updating table. I need to update table by comparing date and name with another table. I have two tables: table 1 : dim_sesid name(varchar) role ...
7
votes
3answers
1k views

Oracle's left join and where clauses errors

CREATE TABLE "ATABLE1" ( "COLUMN1" VARCHAR2(20 BYTE), "COLUMN2" VARCHAR2(20 BYTE) ); CREATE TABLE "ATABLE2" ( "COLUMN1" VARCHAR2(20 BYTE), "COLUMN2" VARCHAR2(20 BYTE) ); ...
2
votes
2answers
425 views

get column from too many tables in mysql

.I have too many tables X1,X2,...Xn (they might exceed 75 tables) in Mysql DB to represent departments of a very large company. every table has structure something like this desc X1; ...
1
vote
1answer
161 views

How should row-specific metadata be created handled for an outer join view?

I have two tables, a large (millions) table of Tickets for orders, and a small (hundreds of thousands) table for Invoices metadata on a subset of those tickets. The metadata is information about when ...
26
votes
8answers
21k views

What is the difference between an INNER JOIN and an OUTER JOIN ?

I am new to SQL and wanted to know what is the difference between those two JOIN types? SELECT * FROM user u INNER JOIN telephone t ON t.user_id = u.id SELECT * FROM user u LEFT OUTER JOIN ...
3
votes
3answers
372 views

How can I select all online friends?

I'm currently working on a social network software written in PHP & MySQL, and it's all pretty fine, but one thing I'm stuck about is online friends. My tables looks following Users ...
10
votes
3answers
4k views

Should I use SQL JOIN or IN Clause?

I have a question about best approach. I am not sure which approach is best when data is considered variable in size. Consider the following 3 TABLES: EMPLOYEE EMPLOYEE_ID, EMP_NAME PROJECT ...
2
votes
1answer
5k views

Using multiple PIVOTs JOINs and GROUP BYs for advanced report generation

I've developed a timesheet recording system, that allows users to record: A Period of time (9:00 to 12:00) What they did during that time (DutyActivity: 1 hour report writing, 2 hours training) ...
2
votes
1answer
292 views

Postgres planer JOIN removal

I have two tables, one contains a lot of rarely update data, and one contains a little of frequently update data. Every record in second table has corresponding record in the first, like following: ...
1
vote
3answers
2k views

Grouping results to get unique rows after multiple joins

this is my first question on dba.stackexchange, hopefully it will be worth it. I am usually a bit more active on Stackoverflow as I am a developer. disclaimer : I don't have full control over the db ...
1
vote
1answer
343 views

Simple select statement not returning correct data

I am trying to return data, where I want the item name (items.name), vendor name (vendors.name), url of the price (prices.url), and the price (prices.price) from 3 different tables (items,vendors and ...
8
votes
2answers
3k views

SQL Server Join/where processing order

After reading Slow SQL query, not sure how to optimize, it got me thinking about the general performance of queries. Surely, we need the results of the first table (when other tables are joined) to be ...
6
votes
1answer
610 views

Why can't we perform joins in a distributed database like Bigtable?

From this answer to What database does Google use?, BigTable is not a relational database. It does not support joins nor does it support rich SQL-like queries. Is this obvious? I do not ...
1
vote
3answers
123 views

Can I automate the “on” statement from MySQL queries?

Background In the process of QA/QC, I am writing lots of queries with multiple joins. I am using MySQL. I would like to know how (if) I can simplify join statements, e.g. by setting default fields ...
4
votes
3answers
2k views

Query to normalize table/combine row text

I have a table (call it oldTable) with columns like so: ID (int),Rank (int),TextLineNumber (int),SomeText (varchar) The primarykey is multi-part: ID+Rank+TextLineNumber. I'm trying to ...
7
votes
2answers
6k views

What is more efficient, a where clause or a join with million plus row tables?

We run a website that has 250MM rows in one table and in another table that we join it to for most queries has just under 15MM rows. Sample structures: MasterTable (Id, UserId, Created, Updated...) ...
2
votes
1answer
526 views

SQL Return Count of Answers with 0's for Choices from another table

My question went dead after one unhelpful answer on SO here I need this to be optimized because it will be called often. It is going into a stored procedure. I am given @slide (tblILDSlide.id) and ...
10
votes
3answers
199 views

Are there any database engines which will intuit the join condition based on the existing foreign keys?

It seems strange to me that, when I've defined a foreign key, the engine cannot use this information to automatically figure out the correct JOIN expressions, but instead requires me to re-type the ...
7
votes
1answer
203 views

Are relations slower than a big, inefficient table?

I've been asked in my job to violate the first normal form (repeating groups across columns, using empty / null values) several times, "for the sake of computer processing power". In a nutshell, a ...
13
votes
2answers
931 views

Peculiar Oracle outer join syntax case

I have seen the following in a query that was supposed to be ported from Oracle outer join syntax to SQL standard outer join syntax: SELECT ... FROM A, B, C, D, E WHERE A.A_ID = B.A_ID AND B.B_ID = ...