Databases

Question 1

How do you add a row to a SQL table?

Answer 1

insert into “table-name” (“columns”…)
values ( ‘value’)

Question 2

What is a tuple?

Answer 2

A single row of a table, which contains a single record for that relation.

Question 3

How do you add multiple rows to a SQL table at once?

Answer 3

INSERT INTO table_name (column1, column2)
VALUES (value1, value2);

Question 4

How do you get back the row being inserted into a table without a separate select statement?

Answer 4

adding returning *; at the end

Question 5

How do you update rows in a database table?

Answer 5

UPDATE table_name
SET some_column = some_value
WHERE some_column = some_value;

Question 6

Why its important to include a where clause in your update statements?

Answer 6

you might update every row

Question 7

How do you delete rows from a database table?

Answer 7

DELETE FROM students
WHERE enrolled_status = ‘not_current’;
Optional
ALTER TABLE students
DROP COLUMN history;

Question 8

How do you accidentally delete all rows from a table?

Answer 8

By typing delete from *

Question 9

What is SQL and how is it different from languages like JavaScript?

Answer 9

SQL (Structured Query Language) is design to managing and manipulating data. It’s not a programing language.

Question 10

How do you retrieve specific columns from a database table?

Answer 10

using SELECT “specific-column”
FROM “table-name”

Question 11

How do you filter rows based on some specific criteria?

Answer 11

Using where clause.
SELECT column1, column2, …
FROM table_name
WHERE condition;

Question 12

What are the benefits of formatting your SQL?

Answer 12

everything looks “clearer”, code is much easier to read

Question 13

What are four comparison operators that can be used in a where clause?

Answer 13

,= ,!= , <=, >=

Question 14

How do you limit the number of rows returned in a result set?

Answer 14

Using limit clause

Question 15

How do you retrieve all columns from a database table?

Answer 15

Using asterisk *

Question 16

How do you control the sort order of a result set?

Answer 16

Using order by clause.
SELECT column1, column2, …
FROM table_name
ORDER BY column1, column2, … ASC|DESC;

Question 17

What is a foreign key?

Answer 17

Foreign key is a link in one table that refers to the primary key in another table .

Question 18

How do you join two SQL tables?

Answer 18

Using join clause followed by table-name

Question 19

How do you temporarily rename columns or tables in a SQL statement?

Answer 19

Using alias e.g “a”.”table-name”

Question 20

What are some examples of aggregate functions?

Answer 20

avg(), count(), min(), max(), sum(),

Question 21

What is the purpose of a group by clause?

Answer 21

The purpose of a group by clause is to group results by one or more column.
SELECT column_name(s)
FROM table_name
WHERE condition
GROUP BY column_name(s)
ORDER BY column_name(s);

Question 22

What is PostgreSQL and what are some alternative relational databases?

Answer 22

Open Source relational database management system that store data and provides access to data points that are related to one another. Alternative are NoSQL databases which store data using mechanism different than tabula relationship for example using data structure key=value pairs

Question 23

What is one way to see if PostgreSQL is running?

Answer 23

Command sudo service postgresql status

Question 24

What is database schema?

Answer 24

It’s a collection of tables, it defines how data in relational database should be organized.

Question 25

What is a table?

Answer 25

A table is a collection of data organized into rows and columns. Tables are sometimes referred to as relations.

Question 26

What are clauses in SQL?

Answer 26

Clauses perform specific tasks in SQL. By convention, clauses are written in capital letters. Clauses can also be referred to as commands.

Question 27

What is SELECT used for?

Answer 27

SELECT is a clause that indicates that the statement is a query. We will use SELECT every time you query data from a database.

Question 28

What is ALTER used for?

Answer 28

The ALTER TABLE statement adds a new column to a table. You can use this command when you want to add columns to a table. The statement below adds a new column twitter_handle to the celebs table.
ALTER TABLE students
ADD exam_grade INT(3);

Question 29

What is ADD COLUMN used for?

Answer 29

ADD COLUMN is a clause that lets you add a new column to a table:
ALTER TABLE friends
ADD COLUMNT email;

Question 30

What is UPDATE USED FOR?

Answer 30

UPDATE is a clause that edits a row in the table.
UPDATE players
SET twitter_handle = ‘@akiz333’
WHERE id = 3;

Question 31

What are constraints used for?

Answer 31

Constraints in SQL are the rules applied to the values of individual columns. They add information about how a column can be used after specifying the data type for a column. They can be used to tell the database to reject inserted data that does not adhere to a certain restriction.
CREATE TABLE celebs (
id INTEGER PRIMARY KEY,
name TEXT UNIQUE,
grade INTEGER NOT NULL,
age INTEGER DEFAULT 10
);

Question 32

What is relational database?

Answer 32

A relational database is a database that organizes information into one or more tables.