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I have a table structure like this


PersonID, referrer


Event_A_ID, PersonID, status


Event_B_ID, PersonID, status

I want to get the event status for everyone from table one with referrer=X by joining all of the event tables like Event_A...K and checking for PersonID. Since people can appear in multiple events we can have cases like this

PersonID=1001, EventA_ID, referrer=X, status
PersonID=1001, EventB_ID, referrer=X, status
PersonID=1001, EventK_ID, referrer=X, status
PersonID=1002, ...
PersonID=1003, ...

But I am not sure how to JOIN all of the event tables since the IDs can be duplicates (and are desired).

I tried to make a separate select and use the in syntax

AND PersonID IN (SELECT PersonID from table1 where referrer=X)

But then I realized everything before will be an aggregate of events.

Should I start with the SELECT from Table1? Select the valid IDs first and then select from the events after? If so, how do I JOIN? I feel like ideal looks like union of all the event tables and then select

use union all and then apply join

select a.person_id,a.referrer,b.eventID,b.PersonID,b.status from Table1 a inner join
select Event_A_ID as eventID, PersonID, status from Table2
union all
select Event_B_ID as eventID, PersonID, status from Table3
)b on a.personid=b.personid

An Intro to Resolving Duplicate Results in SQL Queries, I needed to return a lot of data in this query, and it included joins across several tables. Some of the tables that I was joining had one to many� select a.comm, b.fee from table1 a inner join table2 b on Note that the where condition is not needed. To check for duplicate run the script: select country, count(*) from table1 group by country having count(*)>1 select country, count(*) from table2 group by country having count(*)>1

You can use union all for row wise implementation of data or you can also use inner joins between tables if there is not much table events. This will represent data in column format.

SELECT * FROM tb2 AS t2 INNER JOIN tb3 t3 ON t2.personId = t3.personId INNER JOIN tb1 t1 ON t1.personId = t2.personId WHERE t1.refer='refer1'

There can be many other approach too depending on the number of tables you want to join.

You should also consider to use a better relations among your db tables as your current scenario will lead you to have as many tables as many events you have. This will create slowness in retrieving the data for multiple events.

How to Find Duplicate Values in a SQL Table, Do you need a combination of two columns to be unique together, or are you simply searching for duplicates in a single column? In this example, we are searching� In the self-referencing method, we take two references to the same table and join them using column-by-column mapping with the exception of the ID which is made less than or greater than the other. Let us look at the self-referencing method to find duplicates which looks like this:

You can do something like this with left joins:

SELECT t1.PersonID, t1.referrer, 
t2.Event_A_ID, t2.status as status_a, 
t3.Event_B_ID, t3.status as status_b
FROM table1 t1
LEFT JOIN table2 t2 ON t2.PersonID = t1.PersonID
LEFT JOIN table3 t3 ON t3.PersonID = t1.PersonID
WHERE t1.referrer = 'x'

Working with the LEFT JOIN in SQL, When we use a LEFT JOIN in SQL, we are still joining data. Duplicate values inflate our output with repeating records and do not contribute Non-necessary. Since I expected, and needed, a single result from the query this was a problem. Here’s an explanation of why this bug occurred, and several different ways it can be resolved. My first attempt to remove the duplicates was to add the DISTINCT keyword to my query, but that didn’t fix the problem – I was still seeing duplicates.

More dangerous subtleties of JOINs in SQL — petralia, This is not true: SQL joins will give you at least as many rows as the join specifies . once for each "Tissues" row in the left table, yielding two duplicated rows. If they don't match, you have produced join misses and need to� I am using Office 365 and once I combine the sheets and then merge duplicates; I have the delimiter appear in most of the cells when there is no duplicate. Below is an example of 2 columns that should not have the delimiter after the information:

duplicate rows occuring when using inner join, I need to display these column comm,fees using the country, but my problem here is I used a innerjoin I am getting duplicate rows as I was going� We have multiple tables that need to be combined into a single table using left joins. There are many one to many relationships. Naturally - after the first join the subsequent join will produce duplicate rows. The end result is a massive table with mostly duplicates. I understand these can be removed easily in 2 ways. 1.

Find duplicate data in MySQL, There are many a occasions when you need to find duplicate values INNER JOIN and DISTINCT, and also how to count duplicate values� The problem is that I have duplicates when I try to do something like this: SELECT employees.*, companies.* FROM companies LEFT JOIN employees on = employees.id_company LEFT JOIN company_technologies ON = company_technologies.id_company WHERE company_technologies.id_technology IN(1,2,3)

  • Consider whether tables 2 & 3 should really be separate. Anyway, you can squish them together with UNION ALL
  • this is what i tried but it doesn't work for what I want
  • May you please send complete database structure with sample data?