Class 06

Question 1

what is char(n)?

Answer 1

fixed string

Question 2

what is varcar(n)?

Answer 2

variable string

Question 3

what is a float?

Answer 3

real numbers

Question 4

what should always be included in a table?

Answer 4

a primary key

Question 5

what is a unique constraint?

Answer 5

you want something to appear once

Question 6

what is a foreign key?

Answer 6

reference to another table

(can match primary key values in other tables + may have nulls)

Question 7

what is “not null”?

Answer 7

a participation constraint useful for attributes

Question 8

what is “current_timestamp” useful for?

Answer 8

time stamps you can backtrack to

Question 9

what is “alter table” for?

Answer 9

allows to modify a table structure

Question 10

what is “add” for?

Answer 10

“add” a new field

Question 11

what is “insert into (2)” for?

Answer 11

inserts tuples into tables

Question 12

how can you update your code?

Answer 12

1. “update” relation
2. “set” list_on_assignments
3. “where” selection_condition;

Question 13

what does “delete” do?

Answer 13

removes matching rows from a table where conditions are met

1. “delete from” person
2. “where” id = ‘1234’ ;

Question 14

what does “truncate table” do?

Answer 14

removes all data rows in a table but the table still exists (schema (structure) remains the same)