Question

I have questions for SQL

1. What function does a where clause serve in a SQL query?
2. What is the difference between a “left join” and an “inner join”?
3. Why do data base designers perform normalization?
4. Describe in your words what a “group by column list” function is?
5. What is the default order of the “order by clause”?
6. Describe a “union all” and it’s function?
7. What is an “alias” used for?

Answer 1

1)

SQL query is the combination of clauses, condition. The clauses are SELECT, UPDATE, ALTER, FROM, WHERE etc. The WHERE clause is used to gives conditions in order to filter data from the database. It helps to restrict the number affected by a SELECT, UPDATE or DELETE query. WHERE clause can be used with other logical operators such as AND and OR.

2)

Joins in SQL is used to combine rows from two or more tables, based on a common field. Different types of joins are available in SQL. Left Join is used to return all the rows from the left tables, even if there are no matches in the right. Inner Join is used to return rows when there is a match in both the tables.

3)

In database the goal of normalization is to reduce and eliminate data redundancy. It is a technique of organizing the data in the database in efficient manner. It’s a process to decompose the tables to eliminate data redundancy and unwanted characteristics like Insertion, Update, and Deletion Anomalies.

4)

The group by clause is used in SQL in collaboration with SELECT to arrange the identical data into groups. The group by often used with aggregate functions to group the result set by one or more columns.

SELECT column_name(s)

FROM table_name

WHERE condition

GROUP BY column_name(s);