<p>如何取得所有來自customers1和customers2的產品（包括他們的客戶名稱）？ </p> <pre class="brush:php;toolbar:false;">customer1 table cid name1 1 john 2 joe customer2 table cid name2 p1 sandy p2 linda product table pid cid pname 1 1 phone 2 2 pencil 3 p1 pen 4 p2 paper</pre> <p>結果應該是這樣的</p> <pre class="brush:php;toolbar:false;">pid cid pname name1 name2 1 1 phone john NULL 2 2 pencil joe NULL 3 p1 pen NULL sandy 4 p2 paper NULL linda</pre></p>

SELECT pid, cid, pname, name1, name2 
FROM customer1 c1, product p 
WHERE p.cid=c1.cid 
UNION SELECT pid, cid, pname, name1, name2 
FROM customer2 c2, product p 
WHERE p.cid=c2.cid;

SELECT p.pid, p.cid, p.pname, c1.name1, c2.name2
FROM product p
LEFT JOIN customer1 c1 ON p.cid = c1.cid
LEFT JOIN customer2 c2 ON p.cid = c2.cid