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Join each row with each other row


Join each row with each other row

By : Zaw Moe Naing
Date : October 18 2020, 06:10 AM
To fix this issue Assume that we have a simple data table: , Three possible solutions:
code :
# one
d[, .(c = d$a, d = d$b), by = .(a, b)]

# two
d[, setnames(d, c("c","d")), by = .(a, b)]

# three
d[, setNames(as.list(d), c("c","d")), by = .(a, b)]
   a b c d
1: 1 A 1 A
2: 1 A 2 B
3: 1 A 3 C
4: 2 B 1 A
5: 2 B 2 B
6: 2 B 3 C
7: 3 C 1 A
8: 3 C 2 B
9: 3 C 3 C
d[, setnames(copy(d), c("c","d")), by = .(a, b)]
merge.data.frame(d, d, by = NULL)


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What's the difference between INNER JOIN, LEFT JOIN, RIGHT JOIN and FULL JOIN?

What's the difference between INNER JOIN, LEFT JOIN, RIGHT JOIN and FULL JOIN?


By : user2970758
Date : March 29 2020, 07:55 AM
fixed the issue. Will look into that further Reading this original article on The Code Project will help you a lot: Visual Representation of SQL Joins.
Nested INNER JOIN vs INNER JOIN vs WHERE: correctness, performance, clarity for a particular case (not a typical JOIN vs

Nested INNER JOIN vs INNER JOIN vs WHERE: correctness, performance, clarity for a particular case (not a typical JOIN vs


By : Fiskani Lawrence Chi
Date : March 29 2020, 07:55 AM
Hope this helps All database engines I've been closely working with (this is SQL Server, Oracle, PostgreSQL, MySQL, Sybase, SQLite, Informix and Firebird) will optimize it to the same plan.
The fourth query, however, won't parse on all engines (you cannot reference a table in an ON clause before it had been used in a JOIN clause)
why Indexed Nested-Loop Join only applicable for equi-join or natural join?

why Indexed Nested-Loop Join only applicable for equi-join or natural join?


By : JAC
Date : March 29 2020, 07:55 AM
will help you You are quoting slides for Database Systems Concepts (c) Silberschatz, Korth and Sudarshan.
We want the DBMS to calculate a join. There are lots of special cases where it can do it various ways. These might involve whether there are indexes, selection conditions, etc.
Full Outer Join (left join union right join) MySQL multiple tables

Full Outer Join (left join union right join) MySQL multiple tables


By : user3793895
Date : March 29 2020, 07:55 AM
around this issue Just have a look at Below query, Hope this may help you! Later you can Modify Accordingly
This will join to all 5 tables. Here I kept Location as the Left Table so that All locations will be Displaying after firing this query and matching Id's will be matched to this table.
code :
SELECT * FROM location LEFT JOIN location_type ON location_type.type_id=location.loc_id
    LEFT JOIN hours ON location.loc_id=hours.loc_id 
    LEFT JOIN holiday ON holiday.loc_id=location.loc_id 
    LEFT JOIN holiday_hours ON holiday.hol_id=holiday_hours.holiday_id
Joining three tables, one join uses cte, other join is normal. How do i join this third table to my existing query which

Joining three tables, one join uses cte, other join is normal. How do i join this third table to my existing query which


By : Ron Vanda
Date : March 29 2020, 07:55 AM
Any of those help The data is simple. tblLog is a log with UserID, Time, and Action. tblRole has UserID and Role and a Date field. tblActionDesc has Action and ActionDesc (description). I want the query to give me the information in tblLog but also include the Role from tblRole (for each UserID) and the ActionDesc from tblActionDesc (for each Action). , How about this:
code :
 with cte1 as (
    -- Get the most recent TransDate for each UserID.
    select UserID, max(TransDate) as max_trans_date
    from tblRole
    group by UserID
),
cte2 as (
    -- Now that we know the most recent record for each user, 
    -- get the actual data (i.e. "Role") for each UserID.
    select r.UserID, r.[Role]
    from tblRole as r
        inner join cte1 on r.UserID = cte1.UserID and r.TransDate = cte1.max_trans_date
)
select l.ID, l.UserID, l.[Time], l.[Action], cte2.[Role], ad.ActionDesc
from tblLog as l
    left join cte2 on l.UserID = cte2.UserID
    left join tblActionDesc as ad on l.[Action] = ad.[Action]
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