select multiple rows from tow tables mysql - mysql

Question

I'm trying to select mltiple rows from tow table :
first table is donor
CREATE TABLE donor(
donor_number INT NOT NULL AUTO_INCREMENT,
d_name VARCHAR(30) NOT NULL,
mobile_number INT NOT NULL,
blood_group VARCHAR(20) NULL,
dob DATE NOT NULL,
gender ENUM('male','female') NOT NULL,
govid INT(10) NOT NULL,
PRIMARY KEY (donor_number )
);
second table is blood_donation
CREATE TABLE blood_donation(
donor_number INT NOT NULL,
date_of_donate DATE NOT NULL,
blood_group VARCHAR(20) NULL,
serial_number INT(10) NOT NULL,
blood_component ENUM('wb','prcb') NOT NULL,
PRIMARY KEY (donor_number , date_of_donate ),
FOREIGN KEY (donor_number) REFERENCES donor(donor_number)
);
with this select statement:
SELECT
serial_number,
blood_group
FROM blood_donation
WHERE date_of_donate = '2012-07-18'
UNION ALL
SELECT
blood_group
FROM donor
WHERE donor.donor_number=blood_donation.donor_number;
but, I get error
SQL state 42S22: Unknown column 'blood_donation.donor_number' in 'where clause'
any idea????

Answer 1

Actually you should not be using UNION but JOIN :)
you query will look like this
SELECT
blood_donation.serial_number,
donor.blood_group
FROM
blood_donation ,
donor
WHERE donor.donor_number = blood_donation.donor_number AND date_of_donate = '2012-07-18' ;

Answer 2

A UNION is used to combine more than one result set into a single result set - and each result set must have the same set of columns.
What you need is a JOIN, which is how you link multiple tables together on foreign keys etc and would be something like this:
SELECT
serial_number,
blood_group
FROM blood_donation
INNER JOIN donor ON donor.donor_number=blood_donation.donor_number
WHERE date_of_donate = '2012-07-18'

Answer 3

SELECT
dd.serial_number,
dd.blood_group
FROM blood_donation dd
inner join
donor d
on d.donor_number=dd.donor_number
WHERE dd.date_of_donate = '2012-07-18';
UNION is not what exactly you need, Read some more about JOINS. Also please change the selection alias of columns as per the need. And you can use Left Join instead of Inner Join if you don't want a mandatory join condition on tables.