PHP and MySQL Select a Single Value

Question

I d like to know how to select a single value from my MySQL table  The table includes columns username and id amongst others  id is auto-increment and username is unique   Given the username  I want to set a session variable   SESSION  myid   equal to the value in the id column that corresponds to the given username  Here s the code that I ve already tried    session start     name     GET  username     sql    SELECT  id  FROM Users WHERE username   name     result   mysql query  sql    value   mysql fetch object  result     SESSION  myid      value    So far I m getting      Catchable fatal error  Object of class stdClass could not be converted to string    Casting  value to type string does not fix the problem

User · Answer

try this  session start     name     GET  username     sql    SELECT  id  FROM Users WHERE username   name  LIMIT 1     result   mysql query  sql  or die mysql error     if  row   mysql fetch assoc  result             SESSION  myid      row  id

User · Answer

The mysql   functions are deprecated and unsafe  The code in your question in vulnerable to injection attacks  It is highly recommended that you use the PDO extension instead  like so   session start      query    SELECT  id  FROM Users WHERE username    name LIMIT 1    statement    PDO- gt prepare  query    params   array       name    gt    GET  username       statement- gt execute  params    user data    statement- gt fetch       SESSION  myid      user data  id      Where  PDO is your PDO object variable  See https   www php net pdo mysql for more information about PHP and PDO   For extra help   Here s a jumpstart on how to connect to your database using PDO    database username    YOUR USERNAME    database password    YOUR PASSWORD    database info    mysql host localhost dbname YOUR DATABASE NAME   try        PDO   new PDO  database info   database username   database password     catch PDOException  e           Handle error here

User · Answer

When you use mysql fetch object  you get an object  of class stdClass  with all fields for the row inside of it    Use mysql fetch field instead of mysql fetch object  that will give you the first field of the result set  id in your case   The docs are here

User · Answer

You do this by using mysqli fetch field method   session start     link   mysqli connect  localhost    my user    my password    world     name     GET  username     sql    SELECT  id  FROM Users WHERE username   name  limit 1    result   mysqli query  link   sql   if   result     false         value   mysqli fetch field  result         SESSION  myid      value      Note  you can do that by using mysql fetch field   method as well  but it will be deprecated in php v5 5

User · Answer

mysql   extension has been deprecated in 2013 and removed completely from PHP in 2018  You have two alternatives PDO or MySQLi    PDO  The simpler option is PDO which has a neat helper function fetchColumn       stmt    pdo- gt prepare  SELECT id FROM Users WHERE username       stmt- gt execute     GET  username        value    stmt- gt fetchColumn      Proper PDO tutorial  MySQLi  You can do the same with MySQLi  but it is more complicated      stmt    mysqliConn- gt prepare  SELECT id FROM Users WHERE username       stmt- gt bind param  s     GET  username      stmt- gt execute     data    stmt- gt get result  - gt fetch assoc     value    data    data  id     null    fetch assoc   could return NULL if there are no rows returned from the DB  which is why I check with ternary if there was any data returned

User · Answer

Try this   value   mysql result  result  0

User · Answer

Don t use quotation in a field name or table name inside the query  After fetching an object you need to access object attributes properties  in your case id  by attributes properties name     One note  please use mysqli   or PDO since mysql   deprecated  Here it is using mysqli   session start    mysqli report MYSQLI REPORT ERROR   MYSQLI REPORT STRICT    link   new mysqli  localhost    username    password    db name     link- gt set charset  utf8mb4       always set the charset  name     GET  username     stmt    link- gt prepare  SELECT id FROM Users WHERE username   limit 1     stmt- gt bind param  s    name    stmt- gt execute     result    stmt- gt get result     value    result- gt fetch object      SESSION  myid      value- gt id    Bonus tips  Use limit 1 for this type of scenario  it will save execution time

User · Answer

It is quite evident that there is only a single id corresponding to a single username because username is unique   But the actual problem lies in the query itself-   sql    SELECT  id  FROM Users WHERE username   name      O P   ----    id    ----    id    ----    i e   id  actually is treated as a string not as the id attribute   Correct synatx    sql    SELECT  id  FROM Users WHERE username   name      i e  use grave accent    instead of single quote      or   sql    SELECT id FROM Users WHERE username   name      Complete code  session start     name     GET  username     sql    SELECT  id  FROM Users WHERE username   name     result   mysql query  sql    row mysql fetch array  result   value    row 0     SESSION  myid      value

[php] PHP and MySQL Select a Single Value

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