如何在PHP数组中存储和处理查询结果？

Question

My SQLite query in PHP goes like this:

function getTableData($l_name) {
   $db = new PDO("sqlite:../db/mydb.sqlite");
   $results = $db->exec("SELECT * FROM Locations WHERE L_ID = '" . $l_name; . "');";
   .......
}

My questions are:

• How can I get an array of Locations based on the $results ? Could I just write $results[0] or $results[$results.length] to reference first and last records respectively?
• How would I use a foreach loop to loop through all records? Could I have foreach ($results as $record) , where $record is supposed to be a single record of Location in the current iteration?
• If I were to have a reference to an individual record, say using an array like this records[0] , how would I access this record's field (such as L_Name or L_ID)?

Thank you.

Answer 1

First of all, your code is just incorrect. Here goes the proper version:

$opt = [
    PDO::ATTR_ERRMODE            => PDO::ERRMODE_EXCEPTION,
    PDO::ATTR_DEFAULT_FETCH_MODE => PDO::FETCH_ASSOC,
];
$db = new PDO("sqlite:../db/mydb.sqlite", $opt);
$stmt = $db->prepare("SELECT * FROM Locations WHERE L_ID = ?");
$stmt->execute([$l_name]);

And now you can use $stmt variable in place of $results for your second question:

How would I use a foreach loop to loop through all records? Could I have foreach ($results as $record), where $record is supposed to be a single record of Location in the current iteration?

Yes, you can.

$stmt = $db->prepare("SELECT * FROM Locations WHERE L_ID = ?");
$stmt->execute([$l_name]);
foreach ($stmt as $row)
{
    // do whatever
}

However, this method won't work with your other requirement.

How can I get an array of Locations based on the $results? Could I just write $results[0] or $results[$results.length] to reference first and last records respectively?

To get a real array, you need PDOStatement::fetchAll()‌​ method. However, to get the last element, the syntax will be different:

$stmt = $db->prepare("SELECT * FROM Locations WHERE L_ID = ?");
$stmt->execute([$l_name]);
$results = $stmt->fetchAll();
$first = $results[0];
$last = $results[count($results)-1];

foreach ($results as $row)
{
    // do whatever
}

If I were to have a reference to an individual record, say using an array like this records[0], how would I access this record's field (such as L_Name or L_ID)?

Just reference it. Any time you get a row, you can address its elements this way

echo $row['L_name'];

Answer 2

PDO::exec does not receive the result set returned by the query. What you want is to use either the PDO::query methods or the PDO::prepare method, both of which give you a PDOStatement to work with. That in turn is traversable, allowing you to do something like:

$statement = $dbh->prepare("SELECT * FROM Locations WHERE L_ID = :id");
$statement->bindParam(':id', $l_name);
$statement->execute();

// Traverse the result set
while ($row = $statement->fetch()) {
    // Do something with each $row here
}

// Alternatively, you can load all results into an array:
$results = $statement->fetchAll();

Also notice that the example above uses PDOStatement::bindParam to use your variable with the query. This is vital to preventing SQL injection attacks. You can read more about that here: http://php.net/manual/en/security.database.sql-injection.php

Answer 3

Here is basic code that loops through the results of your query, allowing you to reference fields in each record returned:

foreach ($db->$query("SELECT * FROM Locations WHERE L_ID = '" . $l_name . "'") as $row)
{
    // $row will contain an array to the current record
    // Address fields using the field name in quotes inside the brackets next to $row
    $variable1 = $row['field1name'];
    $variable2 = $row['field2name'];
}