SQL joining without common keys

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If I have a table with the following atributes:

A: id, race, key1 B: key1, driving_id C: driving_id, fines

why would it be possible for us to have the following queries:

select A.id, A.race, B.key1, B.driving_id, C.fines
from A 
left join B on A.key1=B.key1
left join C on B.driving_id= C.driving_id

even though there are no common keys for A and C in the last line of the SQL query?

The query that you have written is parsed as:

select A.id, A.race, B.key1, B.driving_id, C.fines
from (A left join
      B
      on A.key1 = B.key1
     ) left join
     C 
     on B.driving_id = C.driving_id;

That is, C is -- logically -- being joined to the result of A and B. Any keys from those tables would be valid.

Although your original query is the preferable way to write it, you could also write:

select ab.id, ab.race, ab.key1, ab.driving_id, C.fines
from (select . . .  -- whatever columns you need
      from A left join
           B
           on A.key1 = B.key1
     ) ab left join
     C 
     on ab.driving_id = C.driving_id;

The three versions are all equivalent, but the last one may help you better understand what is going on with joins between multiple tables.

Join two table without common field?, Am I misreading your requirements? - Gus "GSquared", RSVP, OODA, MAP, NMVP, FAQ, SAT, SQL, DNA, RNA, UOI, IOU,  Introduction. In this blog, we will understand what a SQL Join is and how to join two or more SQL tables without using a foreign key. We will look into the various types of join as well.

Without seeing sample data from the three tables, we might not know for sure in the query makes any sense or would even run. Assuming it does run, then there should be nothing wrong with the join logic. For example, it is perfectly possible for table B to have a key key1 which relates to the A table, while at the same time having another key driving_id which relates to the C table. Note that either of these keys (but not both) could be a primary key in the B table, and if not then each key would be a foreign key.

Need help joining two tables without common key – SQLServerCentral, You can join on any column combination you like. You can even join on a condition that does not reference a column at all: SQL Fiddle. MS SQL Server 2008  SQL join tables based on non-key column Last update on February 26 2020 08:07:43 (UTC/GMT +8 hours) In this page we are discussing such a join, where there is no relationship between two participating tables.

The LEFT JOIN keyword returns all records from the left table (tableA), and the matched records from the right table (tableB). Furthermore, Similarly it returns all records from the result of first set, and the matched records from the right table (tableC). The result is NULL from the right side, if there is no match.

So A & C have a link through table B.

To Join two tables without using Primary key, In this page we are discussing about such a join, where there is no relationship between two participating tables. SQL join two tables without keys/relations. Ask Question Asked 10 years, 7 months ago. Active 3 years, 5 months ago. Viewed 58k times 23. 10. I have two tables, one

SQL join tables based on non-key column, The color_id column of the shapes table is a Foreign Key which references the An INNER JOIN returns a result set that contains the common elements of the This SQL query has the similar syntax to other JOIN s, but without the ON clause: Similarly, you can use an on clause with cross join, which also differs from standard SQL. A cross join creates a Cartesian product -- that is, every possible combination of 1 row from the first table and 1 row from the second.

JOIN TWO TABLES WITHOUT COMMON COLUMN, relation(nothing in common) in a proper manner. That's no high tech. You can do cartesian and I am pretty sure that's not what you want.=20. Now, if you have a foreign key declared, joining on those linked columns is called a natural join an that is the most common scenario for a join. But as you have seen, it is not the only possibility. Independent of declared relational integrity, you want to make sure that your tables are indexed appropriately to support the (join) queries your

Part 12 Can we join two tables without primary foreign key relation , With SQL Server 2005 you could use common table expressions and the row_number() functions and join on that: with OrderedFoos as ( select row_number() over (order by FooName) RowNum, * from Foos (nolock) ), OrderedBars as ( select row_number() over (order by BarName) RowNum, * from Bars (nolock) ) select * from OrderedFoos f full outer join

Comments
  • Yes, of course. Have you tried it?
  • Why: Transitive property. B lets you get from A to C by translating key1 to driving_ID
  • Thanks for the clear explanation! I was confused initially when I read that SQL is a declarative language and not a procedural one. Would we be able to implement the joins if we switch the 3rd line with the 4th line? Sorry for asking this as I am unable to access my database now.
  • @Anthony . . . Assuming you are referring to your version of the query, then "no". You would get an error to the effect that the table alias c is not defined.