where子句中的列'id_f'是不明确的

Question

i have a join query using 3 table but i get this problem Column 'id_f' in where clause is ambiguous

$id_f=$_GET['id_f'];

$query="SELECT *, s.name AS van, st.name AS naar, p.titl, p.vname
FROM p1_users, f_confirm AS v 
INNER JOIN s_steden AS s ON v.van = s.id
INNER JOIN s_steden AS st ON v.naar = st.id
INNER JOIN p1_users AS p ON v.id_f = p.id_f
AND DATE_FORMAT(date,'%Y-%c-%d')WHERE id_f='$id_f'";
$result=mysql_query($query)or die('Wrong query : ' . mysql_error());
$row=mysql_fetch_assoc($result);

can anyone help?

Answer 1

It means, that two or more tables contain column with name "id_f"(in your case that are p1_users and f_confirm ). You need to specify for which table it related, something like this:

AND DATE_FORMAT(date,'%Y-%c-%d')WHERE p.id_f='$id_f'";

Answer 2

You need to use v.id_f or p.id_f in your where clause as two tables have a column of that name so you need to disambiguate.

It actually doesn't matter which one you use in this case as you are doing an inner join .

This might not be a requirement if you use a natural join but I don't suggest using these.

Answer 3

An ambiguous field is a field in a query that is in two or more tables (or subqueries).

you have two options.

1. Use table_name prefix on each ambiguous field (table1.field_x, table2.field_x)
2. Use table alias, and use the alias as prefix on each ambiguous field (alias1.x, alias2.x).

In your example, in the INNER JOIN statement you use the alias for "v.id_f = p.id_f", but then, in the WHERE clause you forget the alias.

Answer 4

The problem is in WHERE clause, after DATE_FORMAT you wrote id_f='$id_f', but you have this column (id_f) in other tables in this query. So the database doesn't know wchich table you really want to use.