CODEWITHSUNDEEP
phpmysqlpdo
Ozzy
Ozzy

Reputation: 8312

Can't understand 0 rows being returned in php/mysql

I was using this method to get row-counts for SELECT statements, but it didn't work correctly for LIMIT statements, so I added code to remove the LIMIT from the sql string, but now it doesn't work at all!

When I started using queries with a LIMIT X, X at the end, I had to add the section at the top to strip that part from the query, because this method only returns one column - count - but the LIMIT offset would cause it to return nothing.

function dbRowsCount($sql, $data) {

    # removes "LIMIT X,X" from query
    $no_limit_sql = $sql;
    $pos = stripos($sql, " LIMIT");
    if ($pos!==false) {
        $no_limit_sql = substr($sql, 0, $pos).";";
        # logErrors("original sql=".$sql);
        # logErrors("pos=".$pos."<br>new sql=".$no_limit_sql);
    }

    # query SELECT COUNT(*) instead of SELECT...
    # returns row-count
    $regex = '/^SELECT\s+(?:ALL\s+|DISTINCT\s+)?(?:.*?)\s+FROM\s+(.*)$/is';     
    if (preg_match($regex, $no_limit_sql, $output) > 0) {
        dbQuery("SELECT COUNT(*) AS count FROM {$output[1]}", $data);
        $result = dbFetch();
        $last_rowcount = (int)$result["count"];
        if ($pos!==false) {
            # logErrors("after regex="."SELECT COUNT(*) AS count FROM {$output[1]}");
            # logErrors("row count=".$last_rowcount);
        }
        return $last_rowcount;
    } else {
        # logErrors("Oops! There was an error:<br>Regex did not match SQL.");
        return -1;
    }
}

This put directly into MySQL gives count=8:

SELECT COUNT(*) AS count FROM tbl_product WHERE 1 ORDER BY last_update DESC;

The output from the dbRowsCount($sql, $data) method shows this query should end up the same:

original sql=SELECT * FROM tbl_product WHERE 1 ORDER BY last_update DESC LIMIT ?, ?;
pos=59
new sql=SELECT * FROM tbl_product WHERE 1 ORDER BY last_update DESC;
after regex=SELECT COUNT(*) AS count FROM tbl_product WHERE 1 ORDER BY last_update DESC;
row count=0

It was working before, it was returning rows=8 without the part I added for removing "LIMIT X,X" from the query, but only when the LIMIT was 0,X. When I tried LIMIT 5,5 it wouldn't fetch the column because of the offset, and now it's returning 0 rows for any values.

I also tried this directly with PDO, it worked correctly for both int and string parameters! But using the PDOStatement->rowCount(). (It's not recommended for SELECT queries, so I used the above dbRowsCount method).

function dbDebugTest() {
    global $db;
    # logErrors("Beginning dbDebugTest()");
    $stmt = $db->prepare("SELECT * FROM tbl_product WHERE 1 ORDER BY last_update DESC LIMIT ?,?");
    $offset = "5";
    $display = "5";
    $stmt->execute(array($offset,$display));
    # logErrors("dbDebugTest() returned rows: ".$stmt->rowCount());
}

What is causing the first method to return 0 rows?

Upvotes: 2

Views: 387

Answers (1)

Ja͢ck
Ja͢ck

Reputation: 173642

All I can see is that when a LIMIT is present you add a semi colon behind the query. Perhaps that's the cause of your problem.

If that's not the problem, assuming dbQuery and dbFetch are working correctly and didn't change, your table is empty? :)

OP Answer I was still forwarding the $data array to the query when there are no params anymore (since I removed LIMIT X, X)

Upvotes: 0

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