MySQL选择在WHERE IN（）中使用

Question

Hello to Everyone.

I have two table, for example;

TABLE Name X

________________
| id |    A    | 
|____|_________|
| 1  | 1,2,4,8 |
|____|_________|

This Query is working in another TABLE Y,

    mysql_query(" Select * from Y where id IN(1,2,4,8) ")

But this in not working,

    mysql_query(" Select * from Y where id IN(Select A from X where id=1) ")

What can I do? Thank You.

Answer 1

A better table design would be:

table X:
--------
id int
someid int

Values in the table would be:

id  someid
--  --------
1   1
2   1
4   1
8   1

Your query could then be mysql_query(" Select * from Y where id IN(Select id from X where someid=1") .

To answer your question -- You appear to be querying from PHP or something similar. Using the table structure you have, you could retrieve the value from table X using mysql_query("Select A from X where id=1") and store the results in a variable. You could then execute a second query, mysql_query(" Select * from Y where id IN(" + yourVar + ") ") .

Answer 2

This is a "Has Many" relationship, so you should have an intermediate join table. The benefit to this structure is on insertions and deletes. In your structure to append or delete from A you'd have you pull the record, change the value and write it back (or write a procedure maybe).

    X       
_________
|  id   |
|_______|
|  1    | 
|_______|               

    Y
_________
|  id   |
|_______|
|  1    | 
|_______|   
|  2    | 
|_______|   
|  3    | 
|_______|   

    X_Y
____________________________
|  id   |  x_id  |    y_id |
|_______|________|_________|
|  1    |   1    |    1    |
|_______|________|_________|  
|  2    |   1    |    2    |
|_______|________|_________|
|  3    |   1    |    3    |
|_______|________|_________|


SELECT * FROM Y INNER JOIN X_Y ON Y.id=X_Y.y_id WHERE X_Y.x_id=1

or

SELECT * FROM Y WHERE id IN (SELECT y_id FROM X_Y WHERE x_id=1)