Reputation: 43

What does this mean in database - ⊆?

What does this symbol in database mean ⊆?

for example for projection in relational algebra :

Π_LR

take a subset of the attributes of a relation R, where L ⊆ R.

Upvotes: 2

Answers (5)

Reputation: 4529

L ⊆ R means literally L is a subset of R.

In order to understand it here is an example, we have two sets A and B:

A = {1, 4, 5}
B = {1, 2, 3, 4, 5}

where A is a subset of B, because all numbers from set A can be found in set B. Also, we can see it as a diagram:

Now we can write it using the math notation:

A ⊆ B

I recommend to have a look on these pages, just to solid your knowledge:

Upvotes: -1

Reputation: 1

L and R make set of attributes

Upvotes: 0

Reputation: 1

L ⊆ R means L is subset of or equal to R.

Upvotes: 0

Reputation: 300569

L ⊆ R means L is a subset of R ('is contained in').

[L could also be equal to the whole of R].

Upvotes: 0

Reputation: 83263

L ⊆ R means L is a subset of R.

For every element in L, the element exists in R.

Upvotes: 9