※ 引述《neweom (新哥)》之铭言：
: 在w3schools这题 https://bit.ly/2D7WLmn 范例中
: SELECT SupplierName
: FROM Suppliers
: WHERE EXISTS (SELECT ProductName FROM Products
: WHERE Products.SupplierID = Suppliers.supplierID AND Price < 20);
: 会得到 24 个 SupplierName的结果
: 但是如果我改写成
: SELECT SupplierName
: FROM Suppliers
: WHERE EXISTS (SELECT ProductName FROM Products,suppliers
: WHERE Products.SupplierID = Suppliers.supplierID AND Price < 20);
: 会得到 29 个 SupplierName的结果
: 多出来的五笔资料Price都 > 20
: 不知道两个SQL语法的差别在哪里，恳请大大指导
下面这一条少了一个内外的KEY join，因为第二个的EXISTS中出现了Supplier Table
所以是括号中的先跑，外面的就没吃到了。
没串到key会怎样?
像第一条的写法如果像这样
SELECT SupplierName
FROM Suppliers
WHERE EXISTS (SELECT ProductName FROM Products
WHERE 1=1
//1=1 没什么意义
AND Price < 20);
Number of Records: 29
条件也是不起作用
第二条想要加Supplier 应该是像这样
SELECT SupplierName
FROM Suppliers s1
WHERE EXISTS (SELECT ProductName
FROM Products,suppliers s2
WHERE Products.SupplierID = s2.supplierID
AND s1.SupplierID = s2.supplierID
AND Price < 20
);