What is the difference between Select and Project Operations

Question

I\'m referring to the basic relational algebra operators here.
As I see it, everything that can be done with project can be done with select.

I don\'t know if

Answer 1

The difference between the project operator (π) in relational algebra and the SELECT keyword in SQL is that if the resulting table/set has more than one occurrences of the same tuple, then π will return only one of them, while SQL SELECT will return all.

Answer 2

select just changes cardinality of the result table but project does change both degree of relation and cardinality.

Answer 3

PROJECT eliminates columns while SELECT eliminates rows.

Answer 4

Select extract rows from the relation with some condition and Project extract particular number of attribute/column from the relation with or without some condition.

Answer 5

selection opertion is used to select a subset of tuple from the relation that satisfied selection condition It filter out those tuple that satisfied the condition .Selection opertion can be visualized as horizontal partition into two set of tuple - those tuple satisfied the condition are selected and those tuple do not select the condition are discarded sigma (R) projection opertion is used to select a attribute from the relation that satisfied selection condition . It filter out only those tuple that satisfied the condition . The projection opertion can be visualized as a vertically partition into two part -are those satisfied the condition are selected other discarded Π(R) attribute list is a num of attribute

Answer 6

Select Operation : This operation is used to select rows from a table (relation) that specifies a given logic, which is called as a predicate. The predicate is a user defined condition to select rows of user's choice.

Project Operation : If the user is interested in selecting the values of a few attributes, rather than selection all attributes of the Table (Relation), then one should go for PROJECT Operation.

See more : Relational Algebra and its operations