将SQL中的行插入PHP中的数组

Question

Can anyone tell me why row[0] has data, but row[1] to row[3] are undefined (empty)?

I have 4 rows in my database having bookid = '35' .

<?php
$mysqli = new mysqli('localhost', 'root', '', 'assignment3');
$query = "select image from images where BookId='35'";
$result = $mysqli->query($query);
$row = $result->fetch_array(MYSQLI_NUM);
echo $row[0];
echo $row[1];
echo $row[2];
echo $row[3];
?>

Answer 1

You need to use fetch_array every time you want to extend to the next row. Using the numeric indices ( 0, 1, 2 ... n ) only retrieve the columns by number in the row.

Try this:

$row = $result->fetch_array(MYSQLI_NUM);
print_r($row); // row 1
$row = $result->fetch_array(MYSQLI_NUM);
print_r($row); // row 2
$row = $result->fetch_array(MYSQLI_NUM);
print_r($row); // row 3
$row = $result->fetch_array(MYSQLI_NUM);
print_r($row); // row 4

If this makes sense to you, you can even abstract this into a for loop:

for ($i = 0; $i < 4; $i++) {
    $row = $result->fetch_array(MYSQLI_NUM);
    print_r($row);
}

Answer 2

It is much convenient to use mysqli_fetch_all() , since it returns all the rows as an array in a single step. But it may consume much memory in case of large result-set.

Eg.

<?php
$mysqli = new mysqli('localhost', 'root', '', 'assignment3');
$query = "select image from images where BookId='35'";
$result = $mysqli->query($query);
//MYSQLI_NUM for numerical array,
//This will return both associative and numerical, if not specify any parameters.
$row = $result->mysqli_fetch_all(MYSQLI_NUM);
//this will print all rows
print_r($row);

//now it is valid to call
echo $row[0];
echo $row[1];
echo $row[2];
echo $row[3];
?>

Answer 3

select image from images where BookId='35'

This only returns one column so this is why $row[0] works and $row[1]

You need this:

SELECT * FROM images WHERE BookId = '35'