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[Music]
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hello friends welcome back to our
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channel so in today's session we'll
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discuss about the unary operations of
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relational algebra in dbms
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so unary operations
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in
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relational algebra
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so in the previous session we have
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discussed about the various operations
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of relational algebra so in that we have
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seen the unary operations binary
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operations and set theory operations and
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extended and derived operations
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in that we will see these urinary
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operations first what are meant by these
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urinary operations
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so
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we know that unary operations are the
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operations which done on a single
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relation
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so operations
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perform
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on
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single relation
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single relation so that we call it as a
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urinary operation single relation means
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a single table
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single table right so let us consider
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the table
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let us consider a table with
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some three fields
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so
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the first one is
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some
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roll number
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rno
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and then second one is
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some name
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student name
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and the third one is a
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percentage
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percentage let us take these three
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fields
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okay roll number some one zero one
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some
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sandy
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some 98 percent
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one zero two
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some hundred percent
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104
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ashok
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99
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one zero five
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hurry
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forty percent
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right so let us take this relation a
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student relation right so now what are
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the operations that can be performed on
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this particular relation only single
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relation right so let it be the relation
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name is
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student
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student
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relations let's take here some
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85 percentage
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and let us take this one
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with a
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70 percentage okay so there is a slight
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difference in the parts percentages now
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the first operation is
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selection operation
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selection operation and usually this
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selection operation is represented as
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sigma
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sigma
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right
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so
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it is represented as
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sigma
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and this is nothing but the horizontal
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subset of this relation horizontal
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subset means the rows
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so to get the complete rows so we call
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them as a rules or tuples or entities
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right so in order to get the entities or
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in order to get the rows in order to get
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the tuples we have to use this
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sigma selection operation so it is a
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horizontal subset horizontal
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subset
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right the syntax for this selection is
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sigma and here we need to write the
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condition
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condition
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and here you need to write the
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relation mean
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relation name
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right condition and the relation name so
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if you want to get all the records from
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this particular relation
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so
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to get all records
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from relation
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the
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formula is sigma
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followed by
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student
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so we are not giving any condition here
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so it automatically it will get all the
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records of a student
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okay if you are not specifying any
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condition it will get all the
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records of a student now
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now
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if we want to get all the records from
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the relation
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whose percentage
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is
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less than
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90.
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so we need to get
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the records
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get the records of the students
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from the relation whose percentage is
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less than 90 now
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here we have to write the condition but
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the condition here percentage less than
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90
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from this
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from the relation
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student
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student so this is the
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a simple
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relation i mean simple formula to get
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the records of a student
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from the student record whose percentage
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is less than 90
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right so
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like this we can use a multiple
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conditions here
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okay so by using the logical operators
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and
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all
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okay so by using this two
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end and r we can use the logical
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operators and here we need to write the
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condition so this is a simple condition
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this is a simple condition
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right so
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this selection operation is used to get
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the horizontal subset that is a records
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records
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the second one is
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the second one is
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projection operation
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projection operation and it was
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represented as a pipe
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pi
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this was represented as
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pi
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and this is a vertical subset
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it gives the
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vertical subset vertical subset means
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columns so which columns to be
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represented or which columns to be
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uh get in the result right so in the
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result we if we don't want to get all
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the complete columns we can restrict the
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columns that which we want to display on
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the screen by using this projection
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operation so that that's why we call it
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as a vertical subset so here
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we are not writing any condition simply
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we have to write the pi
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and give the column 1
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comma column 2 etc etc
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from
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the relation
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from the
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given
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relation right
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relation
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mean
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so this is
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how we can restrict the columns for
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example
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if you want to get only if you want to
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display only the roll number
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simply you used to
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see
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display
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roll number
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and percentage
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so simply you have to use a pipe
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give the roll number
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comma percentage followed by relation
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name student
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right so this is how we can get only
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the
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columns roll number and percentage and
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if you want to get the display roll
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numbers and percentage
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of
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students of students
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whose percentage
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is greater than 90
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is a greater than 90 so i need to get
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the details of students whose percentage
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is greater than 90 and i just want to
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display only the roll number and
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percentage
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so then simply use pi
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roll number percentage instead of giving
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here the roll number i mean the relation
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use the selection operation sigma
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sigma condition here what is the
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condition percentage
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percentage greater than 90
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from
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student
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so we get the complete details of a
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student whose percentage is greater than
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90 so first this one will be executed
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and from this result it will display
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only the roll number and a percentage
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so hope you understood right so first
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this select query will be executed so
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that will get all the student details
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whose percentage is greater than 90 so
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we'll get
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these two
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results but we need to display only the
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role number and percentage so
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after completion of this query so this
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will be executed so it will display only
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roll number followed by the percentage
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so that is the
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projection operation
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projection operation right so we can
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combine the projection and the selection
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no problem so based upon the query we
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have to write down the formula and the
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next last one is in the unary operations
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in the unary operations the last one is
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so how to rename the
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relation
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rename
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operation rename operation which is
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represented as rho
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okay
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row
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right so here the syntax for renaming
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the relation is
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row
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followed by
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a new name
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followed by
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relation name
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relation name
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right so here example if you want to
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change the student as
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student as
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some
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students okay some students
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so i'll go with the row
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so write it here
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uh let it be some final year
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finally a students okay so i will give
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here the new table name as final fine
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year students
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finally a students final underscore
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students followed by
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student
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so automatically this student name will
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be replaced with final underscore
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student that means it was remake
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it was renamed
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okay it was raining renamed from
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this particular student
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okay so hope you understood this one
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so
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this this is the urinary operations all
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these are the unary operations so
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selection operation projection operation
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rename operations so these operations
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will be performed on a single relation
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so that's why we call these operations
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as
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the
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urinary operations
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so let's stop here so in the next
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session we'll see the sec theory
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operations in relational algebra that is
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intersection union
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cartesian product and a minus
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or a set difference so we'll see all the
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four
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in the next session these are the set
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theory operations so let's stop here so
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hope you understood this complete
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session of unary operations in dbms so
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if you are having any doubt regarding
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this one feel free to post your doubts
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in the comment section definitely i will
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try to clarify all your doubts if you
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really enjoyed my session like my
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you very much