如何使用PHP和Mysql从数据库中获取数据来比较某些值

Question

I have some doubt. Actually i need to fetch data as per column value by joining two table using PHP and MySQL .I am explaining my tables below.

db_specials:

id        special                  type

1        Food and Beverage          1

2        Liquor                     2

db_basic:

 id      special_id     name

 1         2            aaa

 2         1            Raj

 3         2            Ram

 4         2            Jay

 5         1            Nikesh

Here i need to fetch all data from the tables db_basic those are associated with Liquor from first table. I am explaining my code below.

$res=mysqli_query($connect,"select b.id,b.special_id,b.name,s.type from db_basic as b inner join db_specials as s on b.special_id=s.id where b.special_id=2 order by b.id desc");

while($row=mysqli_fetch_array($res)){
   $data[]=$row;
}

I am getting also the proper data. Here problem is db_specials also has the delete functionality on front end with insert. Suppose user deleted the row which has id=2 in db_specials table and insert again,in this case the id will change 2 to 3. So the query also needs to change accordingly. Here i need to know what should be the best logic so that each time user will not change the query if any specials is deleted and inserted again. Please help me.

Answer 1

Instead of id column, you should rely on the type column of db_specials table, since it's not going to be auto incremented for each INSERT operation. So your query should be like this:

select b.id,b.special_id,b.name,s.type 
from db_basic as b 
inner join db_specials as s 
on b.special_id=s.type 
where b.special_id=2 
order by b.id desc

---

Also, I recommend that you should change the special_id column name of db_basic table to type , like this:

+------+------+------+
|  id  | type | name |
+------+------+------+
|      |      |      |

This way, it would be easier for you to construct the query, like this:

select b.id,b.type,b.name
from db_basic as b 
inner join db_specials as s 
on b.type=s.type 
where b.type=2 
order by b.id desc

Answer 2

if user deleted 2,Liquor,2 in db_specials and reinsert, you cannot control what the user input in the front end.
User might be insert Food,2

Instead of join the type column of db_specials with db_basic , you should put a checking in the front end, when user click the delete button, prompt a message before delete 2,Liquor,2 from the table db_specials, if there is any special_id=2 in table db_basic the corresponding rows will deleted as well.