JOIN

Supported Join Types

The join combines columns from two or more tables into a single result set. Databend supports the following join types:

• Inner Join
• Natural Join
• Cross Join
• Left Join
• Right Join
• Full Outer Join
• Left / Right Semi Join
• Left / Right Anti Join

Example Tables

Unless explicitly specified, the join examples on this page are created based on the following tables:

Table "vip_info": This table stores the VIP client information.

Client_ID	Region
101	Toronto
102	Quebec
103	Vancouver

Table "purchase_records": This table lists the purchase records for all the clients.

Client_ID	Item	QTY
100	Croissant	2,000
102	Donut	3,000
103	Coffee	6,000
106	Soda	4,000

Table "gift": This table lists the gift options for the VIP clients.

Gift
Croissant
Donut
Coffee
Soda

Inner Join

The inner join returns the rows that meet the join conditions in the result set.

Syntax

SELECT select_list
FROM table_a
    [INNER] JOIN table_b
        ON join_condition_1
    [[INNER] JOIN table_c
        ON join_condition_2]...

提示

The keyword INNER is optional.

When you join two tables on a common column with the equal operator, you can use the keyword USING to simplify the syntax.

SELECT select_list
FROM table_a
    JOIN table_b
        USING join_column_1
    [JOIN table_c
        USING join_column_2]...

Examples

The following example returns the purchase records of the VIP clients:

SELECT purchase_records.client_id,
       purchase_records.item,
       purchase_records.qty
FROM   vip_info
       INNER JOIN purchase_records
               ON vip_info.client_id = purchase_records.client_id; 

For the definitions of the tables in the example, see Example Tables.

Output:

|102|Donut|3000
|103|Coffee|6000

Natural Join

The natural join joins two tables based on all columns in the two tables that have the same name.

Syntax

SELECT select_list
FROM table_a
    NATURAL JOIN table_b
    [NATURAL JOIN table_c]...

Examples

The following example returns the purchase records of the VIP clients:

SELECT purchase_records.client_id,
       purchase_records.item,
       purchase_records.qty
FROM   vip_info
       NATURAL JOIN purchase_records; 

For the definitions of the tables in the example, see Example Tables.

Output:

|102|Donut|3,000
|103|Coffee|6,000

Cross Join

The cross join returns a result set that includes each row from the first table joined with each row from the second table.

Syntax

SELECT select_list
FROM table_a
    CROSS JOIN table_b

Examples

The following example returns a result set that assigns each gift option to each VIP client:

SELECT *
FROM   vip_info
       CROSS JOIN gift; 

For the definitions of the tables in the example, see Example Tables.

Output:

101|Toronto|Croissant
101|Toronto|Donut
101|Toronto|Coffee
101|Toronto|Soda
102|Quebec|Croissant
102|Quebec|Donut
102|Quebec|Coffee
102|Quebec|Soda
103|Vancouver|Croissant
103|Vancouver|Donut
103|Vancouver|Coffee
103|Vancouver|Soda

Left Join

The left join returns all records from the left table, and the matching records from the right table. The result is NULL records from the right side, if there is no match.

Syntax

SELECT select_list
FROM table_a
    LEFT [OUTER] JOIN table_b
        ON join_condition

提示

The keyword OUTER is optional.

Examples

The following example returns the purchase records of all VIP clients, the purchase records will be NULL if the VIP client has no purchases:

SELECT vip_info.client_id,
       purchase_records.item,
       purchase_records.qty
FROM   vip_info
       LEFT JOIN purchase_records
              ON vip_info.client_id = purchase_records.client_id; 

For the definitions of the tables in the example, see Example Tables.

Output:

|101|NULL|NULL
|102|Donut|3000
|103|Coffee|6000

Right Join

The right join returns all records from the right table, and the matching records from the left table. The result is NULL records from the left side, if there is no match.

Syntax

SELECT select_list
FROM table_a
    RIGHT [OUTER] JOIN table_b
        ON join_condition

提示

The keyword OUTER is optional.

Examples

Imagine we have the following tables:

The following example returns all vip_info of all purchase_records, the vip_info will be NULL if purchase_record does not have the corresponding vip_info.

SELECT vip_info.client_id,
       vip_info.region
FROM   vip_info
       RIGHT JOIN purchase_records
               ON vip_info.client_id = purchase_records.client_id; 

For the definitions of the tables in the example, see Example Tables.

Output:

NULL|NULL
102|Quebec
103|Vancouver
NULL|NULL

Full Outer Join

The full outer join returns all rows from both tables, matching up the rows wherever a match can be made and placing NULLs in the places where no matching row exists.

Syntax

SELECT select_list
FROM   table_a
       FULL OUTER JOIN table_b
                    ON join_condition

提示

The keyword OUTER is optional.

Examples

The following example returns all matched and unmatched rows from both tables:

SELECT vip_info.region,
       purchase_records.item
FROM   vip_info
       FULL OUTER JOIN purchase_records
                    ON vip_info.client_id = purchase_records.client_id;

For the definitions of the tables in the example, see Example Tables.

Output:

Toronto|NULL
Quebec|Donut
Vancouver|Coffee
NULL|Croissant
NULL|Soda

Left / Right Semi Join

The left semi join returns rows from the left table that have a matching row in the right table. The right semi join returns rows from the right table that have a matching row in the left table.

Syntax

-- Left Semi Join

SELECT select_list
FROM   table_a
       LEFT SEMI JOIN table_b
                    ON join_condition

-- Right Semi Join

SELECT select_list
FROM   table_a
       RIGHT SEMI JOIN table_b
                    ON join_condition

Examples

The following example returns the VIP clients (Client_ID & Region) who have a purchase record:

SELECT *
FROM   vip_info
       LEFT SEMI JOIN purchase_records
                    ON vip_info.client_id = purchase_records.client_id;

For the definitions of the tables in the example, see Example Tables.

Output:

102|Quebec
103|Vancouver

The following example returns the purchase records (Client_ID, Item, and QTY) of the VIP clients:

SELECT *
FROM   vip_info
       RIGHT SEMI JOIN purchase_records
                    ON vip_info.client_id = purchase_records.client_id;

For the definitions of the tables in the example, see Example Tables.

Output:

|102|Donut|3000
|103|Coffee|6000

Left / Right Anti Join

The left anti join returns rows from the left table that have NO matching row in the right table. The right anti join returns rows from the right table that have NO matching row in the left table.

Syntax

-- Left Anti Join

SELECT select_list
FROM   table_a
       LEFT ANTI JOIN table_b
                    ON join_condition

-- Right Anti Join

SELECT select_list
FROM   table_a
       RIGHT ANTI JOIN table_b
                    ON join_condition

Examples

The following example returns the VIP clients (Client_ID & Region) who have NO purchase records:

SELECT *
FROM   vip_info
       LEFT ANTI JOIN purchase_records
                    ON vip_info.client_id = purchase_records.client_id;

For the definitions of the tables in the example, see Example Tables.

Output:

101|Toronto

The following example returns the purchase records (Client_ID, Item, and QTY) of non-VIP clients:

SELECT *
FROM   vip_info
       RIGHT ANTI JOIN purchase_records
                    ON vip_info.client_id = purchase_records.client_id;

For the definitions of the tables in the example, see Example Tables.

Output:

|100|Croissant|2000
|106|Soda|4000