sql

Question 1

what is the difference between sql and nosql

Answer 1

One of the differences is that sql has predefined schemas in which the tables have to be written out beforehand and if there are any changes needed to be made you have to alter the table whereas nosql you can add and change as many documents as you want without having to predefine anything.
Another difference is in sql the data is relational and being able to do things like join allows you to match data set by things like ids also offering data integrity to be able to use foreign keys to link users throughout different tables and traceback what they have done While NoSQL databases store data as individual objects that can include nested properties, if a piece of data like a name changes in one object, it might need to be manually updated in all instances where it appears. In contrast, with relational databases, a change at the top level, like in a primary table, can automatically reflect across all related records.
Lastly in sql you have a consistent language for querying like looking up data in spreadsheets or card catalogs whereas in nosql the languages are very diverse and can use multiple different types of built in functions to search for data.

Question 2

What is inner join

Answer 2

inner join will select entries that have matching values on both tables

Question 3

what is left join

Answer 3

left join will return all entries from the left table and any matched entries from the right otherwise null

Question 4

what is right join

Answer 4

right join will return all entries from the right table and any matched entries from the left otherwise null

Question 5

what is full join

Answer 5

full join returns all entries in both tables when there is a match otherwise null

Question 6

what is cross join

Answer 6

cross join will return every possible combination of entries in both tables

Question 7

what is sql

Answer 7

SQL stands for Structured Query Language. It’s used to communicate and interact with relational databases, allowing users to query, insert, update, and delete data.

Question 8

what is dml

Answer 8

dml is data manipulation language, it is the process of making queries in sql to manipulate data

Question 9

what is ddl

Answer 9

ddl is data definition language, it is the process of making queries to manage the table structures

Question 10

what is dcl

Answer 10

dcl is data control language, it is the process of making queries to manage the permissions

Question 11

what is tcl

Answer 11

tcl is transaction control language, it is the process of making queries to manage certain transactions

Question 12

what is a primary key

Answer 12

a primary key is a way to uniquely identify each entry

Question 13

what is a foreign key

Answer 13

a foreign key is a way to create relationships for multiple different tables

Question 14

what is normalization

Answer 14

normalization is a way to be more organized when setting up you tables for instance if you have multiple customers then instead of storing there addresses on each order you would make a customers table to avoid data redundancy like what you see more often in a nosql environment.

Question 15

what is an index

Answer 15

an index is added as a way to find entries quicker and speed up search queries

Question 16

Describe a situation where you would use a GROUP BY clause.

Answer 16

GROUP BY clause in SQL is used when you want to gather rows that have the same value in specified columns into summary rows, like finding the number of employees in each department or the total sales for each customer.

Question 17

Difference between HAVING and WHERE clause.

Answer 17

WHERE: Filters data on the row level before any grouping or summing has been done.
HAVING: Filters data after it has been grouped and summed up.

Question 18

what is a subquery

Answer 18

A subquery, also known as a nested query or inner query, is a query that is embedded within another SQL statement. It can be used to retrieve data that will be used in the main query as a condition to further restrict the data that is retrieved.