MySQL查询以获得所需的结果

Question

I have been working with SQL joins and kinda stuck with following scenario:

Table 1: PK(ID, GRADE)

| ID | Grade | Student_Count |

| 1 | 10th | 20 |
| 1 | 9th | 20 |
| 2 | 10th | 20 |
| 2 | 9th | 20 |

Table 2:PK(ID, Grade, Visited_Date)

| ID | Grade | Visited | Visit_Date |

| 1 | 10th | Yes | 25-Dec-2015 |
| 1 | 10th | No | 26-Dec-2015 |
| 1 | 9th | Yes | 28-Dec-2015 |
| 1 | 9th | No | 29-Dec-2015 |
| 2 | 10th | Yes | 27-Dec-2015 |
| 2 | 9th | No | 30-Dec-2015 |

What i need is a SELECT query which returns data from both the tables for a given ID in such a way that output rows should match the data of the Table 2 (no all possible combinations like cross/dot product) along with non-common columns from Table 1.

For example for ID "1" the output should be:

| ID | Grade | Student_Count | Visited | Visit_date |

| 1 | 10th | 20 | Yes | 25-Dec-2015 |

| 1 | 10th | 20 | No | 26-Dec-2015 |

| 1 | 9th | 20 | Yes | 28-Dec-2015 |

| 1 | 9th | 20 | No | 29-Dec-2015 |

Note : There is no foreign key association between both the tables.

Answer 1

You have to JOIN both tables on the id and grade fields.

SELECT b.ID, b.Grade, a.Student_Count, b.Visited, b.Visit_date
FROM table2 b 
INNER JOIN table1 a 
ON a.ID = b.ID AND a.Grade = b.Grade
ORDER BY a.ID