mysql - 没有 where 子句的连接查询

Question

下面的两个查询输出相同的结果。我理解第一个，但有人可以解释第二个查询是如何工作的吗？

SELECT p0_.name AS name_0
FROM patient p0_ INNER JOIN consultant c1_
ON c1_.id = p0_.consultant_id
WHERE c1_.id=1; 

SELECT p0_.name AS name_0
FROM patient p0_ INNER JOIN consultant c1_
ON (c1_.id = 1)

Answer 1

这两个查询给出相同的结果只是巧合，只是在 patients 表中只有 1 行的情况下。
这些查询是不同的，并给出不同的结果。
请检查这个简单的演示:http://sqlfiddle.com/#!9/1987a/1

CREATE TABLE patient (
  patient_id int,
  name varchar(20),
  consultant_id int
);

insert into patient values(1,'Patient 1', 1); 
insert into patient values(2,'Patient 2', 2); 

CREATE TABLE consultant(
  id int
);

insert into consultant values(1),(2);

---

SELECT p0_.name AS name_0
FROM patient p0_ INNER JOIN consultant c1_
ON c1_.id = p0_.consultant_id
WHERE c1_.id=1; 

|    name_0 |
|-----------|
| Patient 1 |

---

SELECT p0_.name AS name_0
FROM patient p0_ INNER JOIN consultant c1_
ON (c1_.id = 1)

|    name_0 |
|-----------|
| Patient 1 |
| Patient 2 |