SQL FAQ's

1 . What is the purpose of SQL functions?
A1: -SQL functions perform a variety of tasks such as date compares, date formatting, a host of character functions, as well as several numerical functions

2: -What is the DUAL table useful for?
A2: -The DUAL table contains one column and one row and is useful when wanting to run a function once

3: -Explain SQL concatenation.
A3: -Concatenation is when two or more columns are merged together, many times merged with some text items, to form a single column of outout

4: -The DECODE statement is what?
A4: -The DECODE function is the IF-THEN-ELSE logic to SQL

5: -When might you use the HAVING clause?
A5: -to limit the rows returned from a GROUP BY clause


6: -Briefly describe what a JOIN is.
A6: -A join is when two or more tables are required to be used in the same SQL statement

7: -What is 'qualification' and why is it important to a self-join?
A7: -A self-join is where you are joining the same table to itself and you will need to qualify the columns in the where clause so Oracle knows which table a column belongs to

8: -Name the four types of sub-queries.
A8: -those that return a single row; those that return multiple rows; those that return multiple columns in a single row; and those that return multiple columns in multiple rows

9: -What is an IN-LINE view?
A9: -Oracle9i supports a subquery in the FROM clause. This type of SQL statement is also known as an 'INLINE View.'