Database Management

Relational Set Operators

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Relational Set Operators uses relational algebra to manipulate contents in a database. All together there are eight different types of operators. These operators are SQL commands.

The first operator is the UNION. It combines all of the rows in one table with all of the rows in another table except for the duplicate tuples. The tables are required to have the same attribute characteristics for the Union command to work. The tables must be union-compatible which means that two tables being used have the same amount of columns and the columns have the same names, and also need to share the same domain.

INTERSECT is the second SQL command that takes two tables and combines only the rows that appear in both tables. The tables must be union-compatible to be able to use the Intersect command or else it won't work.

DIFFERENCE in another SQL command that gets all rows in one table that are not found in the other table. Basically it subracts one table from the other table to leave only the attributes that are not the same in both tables. For this command to work both tables must be union-compatible.

PRODUCT command would show all possible pairs of rows from both tables being used. This command can also be referred to as the Cartesian Product.

SELECT is the command to show all rows in a table. It can be used to select only specific data from the table that meets certain criteria. This command is also referred to as the Restrict command.

PROJECT is the command that gives all values for certian attributes specified after the command. It shows a vertical view of the given table.

JOIN takes two or more tables and combines them into one table. This can be used in combination with other commands to get specific information. There are several types of the Join command. The Natural Join, Equijion, Theta Join, Left Outer Join and Right Outer Join.

DIVIDE has specific requirements of the table. One of the tables can only have one column and the other table must have two columns only.

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