What is wrong with this concatenate statement? - php

Question

I'm working with a MySQL server Server version: 5.6.42-cll-lve - MySQL Community Server (GPL) and I'm having some major issues with CONCAT()
public function get_urls() {
// Create query
$query = "SELECT a.Name, a.PrimaryVersion, e1.URL
FROM " . $this->table . " a
INNER JOIN
FunnelsFlows b ON a.Funnel_ID = b.Funnel_ID
INNER JOIN
BackendFlows c ON b.BackendFlow_ID = c.BackendFlow_ID
INNER JOIN
BackendLevels d ON CONCAT(c.Level, :lv) = d.BackendLevel_ID
LEFT JOIN
BackendPages e1 ON d.Upsell = e1.BackendPage_ID
LEFT JOIN
BackendPages e2 ON d.Downsell1 = e2.BackendPage_ID
LEFT JOIN
BackendPages e3 ON d.Downsell2 = e3.BackendPage_ID
WHERE
a.Funnel_ID = :fid
LIMIT 0,1";
// Prepare statement
$stmt = $this->conn->prepare($query);
// Bind ID
$stmt->bindParam(':fid', $this->fid, PDO::PARAM_INT);
$stmt->bindValue(':lv', $this->lv, PDO::PARAM_STR);
// Execute query
$stmt->execute();
Running this code throws the following error: PHP Fatal error: Uncaught PDOException: SQLSTATE[42S22]: Column not found: 1054 Unknown column 'c.Level' in 'on clause' in ...
The entire database structure you can view here:
https://app.sqldbm.com/MySQL/Share/wBAF2JMRFFSoPPjIPdYZc0GFrngIE8md_DYjF4jNYw0

Answer 1

Delete the quotes (both for column name and for the value):
CONCAT(a.Level, :level)
Also, you use a wrong parameter name:
$stmt->bindParam(':level', $this->lv, PDO::PARAM_INT);
// ^^^^^

Answer 2

Your query cannot work like that. You are trying to concat a field content CONCAT(c.Level, :lv) with a parameter :lv. This results in a string if there were a column Level. However, you rather want to build a dynamic column name like Level1 / Level2 aso.
Unfortunately this cannot be done by parameters. This is owing to the fact, that query plans are prepared. Changing column names at execution time would alter the query plan.
You either need to build dynamic SQL in such a case or write a complex ON clause.
The ON clause:
ON
(
(:lv = 1 AND c.Level1 = d.BackendLevel_ID)
OR
(:lv = 2 AND c.Level2 = d.BackendLevel_ID)
-- and so on
)
Dynamic SQL:
$sql = 'ON (c.Level' . inval($this->lv) . ' = d.BackendLevel_ID)'
Since PHP's intval function is considered to be safe, I would prefer the latter example in order to improve SQL performance.

Answer 3

What about this?
$query = "SELECT a.Name, b.URL
FROM " . $this->table . " a
INNER JOIN
FunnelsFlows b ON CONCAT(a.Level, ':lv') = b.Level_ID
WHERE
a.Funnel_ID = :fid
LIMIT 0,1";
// Prepare statement
$stmt = $this->conn->prepare($query);
// Bind ID
$stmt->bindParam(':fid', $this->fid, PDO::PARAM_INT);
$stmt->bindParam(':lv', $this->lv, PDO::PARAM_INT);
// Execute query
$stmt->execute();
That was a quick response, so I'll explain now.
What I'm seeing it that you want to concatenate a table column with a string, right?
First you had a wrong ident :level which you are trying to bind with the following statement $stmt->bindParam(':lv', $this->lv, PDO::PARAM_INT); so you have to change it with :lv or chenge the binding statement to $stmt->bindParam(':level', $this->lv, PDO::PARAM_INT);.
Second - while you are trying to concatenate a column you have to remove the quotes so it should be CONCAT('a.Level', and if the second operator is a string it should be in single quotes, so the full CONCAT operator should be written as follow CONCAT(a.Level, ':lv')