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I'm having trouble understanding relational algebra when it comes to theta joins, equijoins and natural joins. Could someone please help me better understand it? If I use the = sign on a theta join is it exactly the same as just using a natural join?
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The primary difference between an inner and natural join is that inner joins have an explicit join condition, whereas the natural join's conditions are formed by matching all pairs of columns in the tables that have the same name and compatible data types, making natural joins equi-joins because join condition are ...
A theta join is a join that links tables based on a relationship other than equality between two columns. A theta join could use any operator other than the “equal” operator.
An equijoin is a join with a join condition containing an equality operator. An equijoin returns only the rows that have equivalent values for the specified columns. An inner join is a join of two or more tables that returns only those rows (compared using a comparison operator) that satisfy the join condition.
Theta Join, Equijoin, and Natural Join are called inner joins.
A theta join allows for arbitrary comparison relationships (such as ≥).
An equijoin is a theta join using the equality operator.
A natural join is an equijoin on attributes that have the same name in each relationship.
Additionally, a natural join removes the duplicate columns involved in the equality comparison so only 1 of each compared column remains; in rough relational algebraic terms: ⋈ = πR,S-as ○ ⋈aR=aS
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