SQL JOIN [Database]


In this page, I would like to describe basic knowledge for SQL join.

🍄 inner join & outer join

I explain based on the following table structure:

CREATE TABLE sell
(   "id" NUMBER,
    "selled_at" DATE,
    "customer_id" VARCHAR2(4)
);

CREATE TABLE customer
(   "id" VARCHAR2(4),
    "name" VARCHAR2(255)
);

inner join gets records with records in both:

select * from sell inner join customer on (sell.customer_id = customer.id);

left outer join extracts all records ofleft table and combines the records from right table.

select * from sell left outer join customer on (sell.customer_id = customer.id);

right outer join extracts all records of right table and combines some records from left table.

select * from sell right outer join customer on (sell.customer_id = customer.id);

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