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 there is a difference or a certain nuance that I ve missed

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The difference between the project operator  p  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 p will return only one of them  while SQL SELECT will return all

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

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PROJECT eliminates columns while SELECT eliminates rows

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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

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In Relational algebra  Selection  and  Projection  are different operations  but the SQL SELECT combines these operations in a single statement    Select retrieves the tuples  rows  in a relation  table  for which the condition in  predicate  section  WHERE clause  stands true   Project retrieves the attributes  columns  specified   The following SQL SELECT query   select field1 field2 from table1 where field1    Value     is a combination of both Projection and Selection operations of relational algebra

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The difference come in relational algebra where project affects columns and select affect rows  However in query syntax  select is the word  There is no such query as project   Assuming there is a table named users with hundreds of thousands of records  rows  and the table has 6 fields  userID  Fname Lname age pword salary   Lets say we want to restrict access to sensitive data  userID pword and salary  and also restrict amount of data to be accessed  In mysql maria DB we create a view as follows   Create view user1 as select Fname Lname  age from users limit 100   from our view we issue  select Fname from users1     This query is both a select and a project

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Project will effects Columns in the table while Select effects the Rows  on other hand Project is use to select the columns with specefic properties rather than Select the all of columns data

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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

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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   R  attribute list is a num of attribute

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Project is not a statement  It is the capability of the select statement  Select statement has three capabilities  They are selection projection join   Selection-it retrieves the rows that are satisfied by the given query  Projection-it chooses the columns that are satisfied by the given query  Join-it joins the two or more tables

[sql] What is the difference between Select and Project Operations

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