Relational Algebra Symbols

The following are the symbols for the relational algebra operators:

OperatorSymbolHTMLUnicodeDescriptionAdditional information requiredMagnification
ProjectionπππSelect some of the columns of a bagThe columns to be selected
ExtensionξξπAdd an additional column to a bagThe formula for computing the additional column
SelectionσσσSelect some of the rows of a bagThe condition (predicate) for selecting rows
RenameρρρChange the name of a columnThe old and new names
Product××ȕCartesian product of two bags+3
Join⨝Join of two bagsThe join condition+2
Left Join⟕Left outer join of two bags+4
Right Join⟖Right outer join of two bags+4
Full Outer Join⟗Full outer join of two bags+4
Semijoin⋉Subquery with exists or "in"+3
Antijoin▷Subquery with not exists or "not in"+1
Union∪∪The rows in each of the bags+1
Intersection∩∩The rows that are in both of the bags+1
Difference––The rows that are in the first bag but not in the second+1
PartitionψψψGroup by, distinct, order byThe columns to be used for partitioning

In Firefox, I found that I had to magnify some of the symbols to make them readable. The magnification I used is shown in the last column above. For example, the unmagnified full outer join is ⟗ but if you write <font size='+4'>&#x27d7;</font> then it looks like this: . The required magnifications are different for IE and google-chrome.

The following table uses image files instead of unicode characters:

OperatorSymbolFileDescriptionAdditional information required
Projectionhttp://www.ccs.neu.edu/home/kenb/cs5200/resources/image/pi.gifSelect some of the columns of a bagThe columns to be selected
Extensionhttp://www.ccs.neu.edu/home/kenb/cs5200/resources/image/xi.gifAdd an additional column to a bagThe formula for computing the additional column
Selectionhttp://www.ccs.neu.edu/home/kenb/cs5200/resources/image/sigma.gifSelect some of the rows of a bagThe condition (predicate) for selecting rows
Renamehttp://www.ccs.neu.edu/home/kenb/cs5200/resources/image/rho.gifChange the name of a columnThe old and new names
Producthttp://www.ccs.neu.edu/home/kenb/cs5200/resources/image/times.gifCartesian product of two bags
Joinhttp://www.ccs.neu.edu/home/kenb/cs5200/resources/image/join.gifJoin of two bagsThe join condition
Left Joinhttp://www.ccs.neu.edu/home/kenb/cs5200/resources/image/leftjoin.gifLeft outer join of two bags
Right Joinhttp://www.ccs.neu.edu/home/kenb/cs5200/resources/image/rightjoin.gifRight outer join of two bags
Full Outer Joinhttp://www.ccs.neu.edu/home/kenb/cs5200/resources/image/fulljoin.gifFull outer join of two bags
Semijoinhttp://www.ccs.neu.edu/home/kenb/cs5200/resources/image/semijoin.gifSubquery with exists or "in"
Antijoinhttp://www.ccs.neu.edu/home/kenb/cs5200/resources/image/antijoin.gifSubquery with not exists or "not in"
Unionhttp://www.ccs.neu.edu/home/kenb/cs5200/resources/image/union.gifThe combined collection of rows in the two bags
Intersectionhttp://www.ccs.neu.edu/home/kenb/cs5200/resources/image/intersection.gifThe rows that are in both of the bags
Differencehttp://www.ccs.neu.edu/home/kenb/cs5200/resources/image/difference.gifThe rows that are in the first bag but not in the second
Partitionhttp://www.ccs.neu.edu/home/kenb/cs5200/resources/image/psi.gifGroup by, distinct, order byThe columns to be used for partitioning