DB -> DataBase = In short, it's a big folder storing data
SELECT/FROM
select * -> used when getting the data. used to all the Query viewing data
from food_orders
* -> Bring all the column
from-> statement to specify the table when bringing data
Selecting necessary parts of the column
select restaurant_name, addr
from food_orders
select (specific name of the column), (specific name of the column), ....
from (table)
Changing the name of the column
To:
select (name of the column) as (changed name), (name of the column) (changed name)
2 ways to change the name
1. (name of the column) as (changed name)
2. (name of the column) (changed name) -> don't use "as"
The point when changing the name
1. English or underbar
Just write as usual -> orb_yes
2. Other language(Korean) or Special characters
Must be covered with "" -> "특수문자"
If searching only certain data under condition, (where)
select *
from customers
WHERE age = 21
for gender,
select *
from customers
WHERE gender = 'male' -> Since male itself is not a column, but a text, it must be covered with ""
WHERE (condition) =
Other ways of filtering methods(Comparison operation, BETWEEN, IN, LIKE)
Comparison operation
= -> same Ex. gender = "female"
<> not same (different) Ex. gender <> "female"
> big Ex. age > 21
>= same or big Ex. age >= 21
< small Ex. age < 21
<= same or small Ex. age <= 21
BETWEEN -> It brings all the data between A and B
IN -> adding the condition" including"
LIKE -> not exactly same but adding the similar data condition
Ex. BETWEEN
Frame - WHERE (table) between (condition) and (condition)
WHERE age between 21 and 23 -> getting the column from age, and bring all the data between 21 ~ 23
Ex. IN
Frame - WHERE (table) in ((condition)) -> must covered by ()
WHERE age in (21, 25, 27) -> only gets the data where the ages are 21, 25, 27
Ex.LIKE
Frame -
1. If it starts with specific start text -> WHERE (table) like '(starting text)%'
2. If it includes a special text -> WHERE (table) like '%including text%'
3. If it ends with specific text -> WHERE (table) like %(starting text)'
Ex. 1
Ex. 2
Ex. 3
Multiple Condition(and, or, not)
AND
select *
from customers c
WHERE age >= 21
and gender = 'male'
and -> It will make all the condition statements work together
OR
select *
from customers c
WHERE age >= 21
or gender = 'male'
Or -> will show all the data that satisfied any of the condition
NOT
select *
from customers c
WHERE not gender = 'male'
not = same as <>
Good night!