INSERT INTO table name with both variables and SELECT FROM - mysql

Question

I'm trying to insert an item into a table using both posted variables and something from another table. I'm not quite sure where I am going wrong because nothing is being added to the table. I'm super confused. Here is my code:
$stmt = $conn->prepare("INSERT INTO Student_Choices (Username,T1_Choice,T2_Choice,T3_Choice,Current_DB)
VALUES (:username,:t1choice,:t2choice,:t3choice, db.DB)
SELECT DB FROM Current_DB as db
");
$stmt->bindParam(':username', $_SESSION['username']);
$stmt->bindParam(':t1choice', $_POST["term1sport"]);
$stmt->bindParam(':t2choice', $_POST["term2sport"]);
$stmt->bindParam(':t3choice', $_POST["term3sport"]);
$stmt->execute();

Answer 1

The SELECT DB FROM Current_DB as db is not valid inside the INSERT sentence. Just execute this query first, then get the DB value into a variable, and finally use it with bindParam() as you do with the other parameters: Something like this:
/* Get the database name. */
$stmt = $conn->prepare("SELECT DB FROM DB_Year");
$stmt->execute();
$res = $stmt->fetchAll();
$db = $res[0]['DB'];
/* Execute the insert statement. */
$stmt = $conn->prepare(
"INSERT INTO Student_Choices (Username, T1_Choice, T2_Choice, T3_Choice, Current_DB)
VALUES (:username, :t1choice, :t2choice, :t3choice, :db)"
);
$stmt->bindParam(':username', $_SESSION['username']);
$stmt->bindParam(':t1choice', $_POST["term1sport"]);
$stmt->bindParam(':t2choice', $_POST["term2sport"]);
$stmt->bindParam(':t3choice', $_POST["term3sport"]);
$stmt->bindParam(':db', $db);
$stmt->execute();

Answer 2

To design this INSERT query, start by using SELECT to create the result set you want to insert.
SELECT :username AS Username,
:t1choice AS t1choice,
:t2choice AS t2choice,
:t3choice AS t3Choice,
DB
FROM Current_DB
Then use that result set as the data source for your insert.
INSERT INTO Student_Choices
(Username,T1_Choice,T2_Choice,T3_Choice,Current_DB)
SELECT :username AS Username,
:t1choice AS t1choice,
:t2choice AS t2choice,
:t3choice AS t3Choice,
DB
FROM Current_DB
Notice how the SELECT operation replaces the VALUES() clause.
(Careful, unless you put an appropriate WHERE clause on the SELECT, you may get lots of rows inserted, one for each row in Current_DB.)