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invalid joins
Had not heard this one A common invalid join is when you are doing up a shirt, and the buttons and the button holes end up not matching. Use this already Another one is Where 1 <> 0 Another one (in current syntax) SELECT * FROM Table1 INNER JOIN Table2 ON 1 <> 0 Did not know Cartesian... -
null value in subqueries
The inner query (select mgr from emp) returns a NULL value, according to the lesson. So, the full query is like the following select ename from emp where empno NOT IN (unknown); Obviously it doesn't make sense to say the result is anything but uknown as well. I almost understand... -
To join n tables together, you need a minimum of (n-1) join conditions
In Oracle, An Introduction to SQL and PL/SQL, there is a discussion of Joins. The statement follows: To join n tables together, you need a minimum of (n-1) join conditions. The use of the words "At Least" Indicates I can do the following: where table1.column1 = table2.column2... -
invalid joins
In An Introduction to SQL and PL/SQL, Oracle, lesson 4 there is a discussion of Cartesian products. The following statement is in the slides. Cartesian Product A Cartesian product is generated if a join condition is omitted OR a join condition is invalid. What is an example of an invalid join? -
null value in subqueries
Please help me understand the following from Oracle Introduction to SQL and PL/SQL, Lesson 7 subqueries. select ename from emp where empno NOT IN (select mgr from emp); no rows returned. Returning Nulls in the Resulting Set of a Subquery The SQL statement above attempts...
