Join Operation

Relational Database 4 | JOIN Operation, Conditional Expressions, Nested  Queries, and Aggregate Operators | by Adam Edelweiss | SereneField | Medium

• The five basic operations (select, project,
+, -, x ) are all we need to make any
relational table
– other operations we can imagine can be
done with combinations of the basic 5
• One combination is so commonly wanted
and useful that we name it and provide it
as a direct operation Join

• Combines two tables (like the Product
operation) but doesn’t necessarily
produce all pairings
– If the two tables each have fields with a
common data type, the new table
combines only the rows from the given
tables that match on the fields – Syntax: Table1 Table2 On Match

• “Bowtie” symbol suggests a special form of
product where the tables “match up”
• Match is a comparison test involving fields
from each table (Table.Field)
• When match is true for a row from each
table it produces a result row that is their
concatenation