SQL 内连接 2 个表

Question

Hoping to get some help with this, I have made a few attempts at an inner join that shows all 'Product' information from the product table for, any product that has sold more than 10 units using an inner join.

PRODUCT TABLE (Columns)
P_CODE, P_DESCRIPT, P_INDATE, P_QOH, P_MIN, P_PRICE, P_DISCOUNT, V_CODE

LINE TABLE (Columns) this table shows the lines/information for each 
invoice

INV_NUMBER, LINE NUMBER, P_CODE, LINE_UNITS, LINE_PRICE, LINE_TOTAL

I understand that I have to make the join using the common key attribute (p_code) but I cannot figure out how to do the sum within the inner join.

Here is my most recent attempt:

SELECT * PRODUCT FROM PRODUCT
INNER JOIN line
ON product.p_code = line.p_code
WHERE sum(line_units) >=10
AND line.p_code = product.p_code;

Error: near "product"; syntax error

Any help would be appreciated, Thank you.

Answer 1

Looks like you have the table name PRODUCT within the SELECT section. And the sum() needs to happen within the SELECT section along with the extra HAVING clause at the end.

SELECT *, sum(line_units) as line_units_sum FROM product
INNER JOIN line ON product.p_code = line.p_code
WHERE line.p_code = product.p_code
HAVING line_units_sum >= 10

Answer 2

The requirement

Show all product information from the product table for any product that has sold more than 10 units.

The solution

Because you only want to build the projection from the product table, and you don't need any column from the line table, you can also use a correlated subquery like the following one:

SELECT *
FROM product
WHERE 10 < (
    SELECT COUNT(*)
    FROM line
    WHERE line.p_code = product.p_code
)

The database optimizer might choose to use a JOIN internally if the cost of the JOIN is lower than other alternatives. So, it does not mean that the query will do row-by-row processing for the outer table records. Only the execution plan can tell how the query is executed by the database engine.