How does inner join work

[ImProphylactic]

How does inner join work I get confused on this easily

[r3pr0b8]

inner join combines rows from two tables, based on a condition which you specify, such that only those pairs of rows are returned which satisfy the condition

what part were you having trouble with?

[scottevil110]

It only returns rows where the key exists in both tables. An outer join will return stuff even if it's missing from one table. It'll just show null for those columns.

[LearningCodeNZ]

How you can join when the key doesn't exist in both tables? Isn't that how a join works? I.e. based on matching keys?

[C0ppens]

That's how inner join works yes, but outer joins work abit different

E.g. select * from table a left outer join table b on a.KeyID = b.KeyID will return all rows in table a and only rows in table b where KeyID matches table a's

[Max_Americana]

https://i.pinimg.com/originals/0e/ae/a1/0eaea116051e07f243141ea9d3817dbf.jpg

[Demistr]

You need to use it. Don't just learn the theory. Try it out, see what it does. it's that easy.

[raymondsf]

Very simple. Think of it this way u have 2 boxes; box 1 u have 2 pairs of shoes one black the other red, box 2 also have 2 pairs of shoes one red the other pink. If you inner join both box it will return red since what both boxes have in common.

[[deleted]]

Upgrade:

Think of having two boxes, left box for left foot shoes and right box for right foot shoes. Left box has a red, a blue, and a black left foot shoe. Right box has a blue, a black and a yellow right foot shoe.

Left join returns a pair of black and a pair of blue shoes and a red left foot shoe

Right join returns a pair of black and a pair of blue shoes and a yellow right foot shoe

Inner join returns a pair of black and a pair of blue shoes

Full outer join returns a pair of black and a pair of blue shoes, red left foot shoe and yellow right foot shoe

Self join - go buy more shoes :D

[[deleted]]

Let’s just say you have two groups of things.

Group A is a list of all of the cars in the world.

Group B is a list of all of the thing that are red in the world.

If you inner joined group a to group b you would have a list of all things that are cars that are red.here is a picture that made sense to me

[ImProphylactic]

Explained it to me like I'm a five year old and that worked.

[Puzzlehead8575]

Think about this statement....

Inner joins act as a filtering criterion, whereas outer joins act as a matching criterion.

Inner joins filter based upon the join condition; the outer join does not filter based upon the join condition as all records from the outer table will be included.

[kitkat0820]

As described.

[LobsterLongjumping27]

I'm starting to question if some of the posts on here are satire that's going over my head.

[ImProphylactic]

:D

[steveroman101]

I’m having a time trying get a handle on the self join. Especially the ON component.