SQL Questions

-


1. When will ROW_NUMBER and RANK give different results? Give an example.
2. Is it possible for LEFT JOIN and FULL OUTER JOIN to produce the same results? Why or why not?
3. Why would I use DENSE_RANK instead of RANK? What about RANK instead of DENSE_RANK?
4. What happens if I GROUP BY a column that is not in the SELECT statement? Why does this happen?
5. LAG and LEAD are especially useful in what type of scenarios?
6. For dealing with NULL values, why would I choose to use IFNULL vs. CASE WHEN?
7. Do temp tables make your code cleaner and faster, one of the two, or none? Why?
8. When is a subquery a bad idea? A good idea?

Comments

Post a Comment

Popular posts from this blog

Sequence

-
Generate Unique Sequential values     Sequence has 2 pseudocolumns     1. CURRVAL     2. NEXTVAL CURRVAL :  gives the most recently generated value NEXTVAL : gives the next available value in the sequence to generate sequence will start generating value from its MINVALUE Default MINVALUE is 1 default incremental value of sequence is +1 Same sequence can be used in multiple tables but not suggestable. One sequence for one table.
Read more

Stored Procedure

-
1. When we have to same task everyday then instead of writing queries we can save the query in procedure and then just run it when required. 2. Named PLSQL program 3. Permanently saved in DB Features :  1. Procedures executed explicitly. Execute Command               Exec Procedurename (arg1, arg2...); 2. Procedures can also executed  implicitly. Using procedured calling statement          Procedurename(arg1, arge2...); 3. Saved in a DB as pre compiled obbject. Complied once only when there is changes in logic of SP then again it will complied. Can call procedure from other proc, func, programs. 4. Procedure can be static or dynamic mean proc may or maynot take arguments. 5. By default proc should not return any value. Types of Proc:  1. Static : Not having arg 2. Dynamic : With arg Syntax : Create or replace procedure procedure_name( arguments ..) is/as  ----------any keyword use declaration  -----declare variables Begin execution statements.... end;
Read more