PDO Postgres-检查列是否存在并根据关闭条件执行操作

Question

I'm trying to check to see if a column exists.. If it does, then I want to update the value, and if it doesn't, I want to alter the table and add the column with the a value. I'm pretty new to PDO, but I'm pretty sure my query is fine, I just don't know how to handle the output from the execute() command I guess. Thanks for the help in advance!

$sth = $pdo->prepare(' SELECT ? FROM `?` WHERE column_name=? ');
$sth->bindParam(1, $column, PDO::PARAM_STR);
$sth->bindParam(2, $livetable, PDO::PARAM_STR);
$sth->bindParam(3, $column, PDO::PARAM_STR);
$sth->execute();

if ($sth) {
    //Row Exist - Update Value
    echo 'Row Exist';
}else{
    //Row Doesn't Exist - Create column & update with value
    echo 'row does not';
}

Answer 1

You cannot pass a table name as a bind parameter like this, you would need to use dynamic SQL to achieve this. But if you just want to check if a column exist in a table, don't query the table directly (what if it contains millions of records ?) ; instead, query Postgres information schema, as follows :

SELECT column_name 
FROM information_schema.columns 
WHERE
    table_name = ?
    AND  column_name = ?;