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Database Programming Section 15 – Oracle Proprietary Join Syntax and Review Join Commands Two sets of commands or syntax used to make connections between tables in a database: Oracle proprietary joins ANSI/ISO SQL 99 compliant standard joins Oracle Proprietary joins Simple join or equijoin SELECT table1.column, table2.column FROM table1, table2 WHERE table1.column1=table2.column2; Equijoin Simple or inner join SELECT clause specifies columns names to retrieve FROM clause specifies the tables to access WHERE clause specifies how tables are to be joined Cartesian Product Join Joins 2 or more tables together without a join conditions Joins every row in table 1 to every row in table 2 Number of resulting rows is M*N where M = number of rows in table 1 and N = number of rows in table 2 You should avoid a Cartesian product by ALWAYS having a valid WHERE clause Restricting rows in Join User AND operator to restrict the number of rows returned in a join. Qualify the column in statement with the table name or alias Table Alias Simply typing lengthy statement using table alias in place of table names. Define table alias in the FROM clause Nonequijoin A non-equijoin than is a join between two tables when column values in each table match a range of values but is not an exact match = operator can not be used by itself Can use <=, >=, BETWEEN…AND BETWEEN…AND most effective SELECT p.code, e.cost FROM d_packages p, d_events e WHERE e.cost BETWEEN p.low_range AND p.high_range; Outer Join Outer join is used to see rows that have a corresponding value in another table plus those rows in one of the tables may have missing data Use a plus (+) after the table’s column name in the WHERE clause of the query Outer join cannot use the IN operator or be linked to another condition by the OR operator Join with plus sign Use the plus sign to indicate the table whose column is missing data SELECT a.column, b.column FROM table1 a, table2 b with on of the following WHERE clauses WHERE a.column(+) = b.column WHERE a.column = b.column(+) NEVER WHERE a.column(+) = b.column(+) CAN’T use IN operator or OR operator in WHERE clause