Database performance from php calls [closed] - php

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I'm wondering about a potential problem I might get. My problem is let's say I have 2 tables one called speakers and clients. In the client table the client has the speaker IDs of 1,5,8(SAVED in a STRING field) - so I'm using explode() to get the values.
So now I have to call the speaker table 3 times to get the values of each speaker. This introduces the problem that it will get very expensive if there is alot of users online wouldn't it?
Is there an alternative to calling a table from an array of items or something?
I'm not too clued up about all the php approaches to this so any help will be appreciated!

Answer 1

I agree with #RiggsFolly that it may not be the best way to store the data, you could do something like this:
SELECT (whatever fields you want or speakers.* for all) FROM speakers JOIN clients ON clients.id=(clients.id) WHERE speakers.id IN (clients.field_with_speakers_list_string);
I believe that will get you going. It should return what you want. You would just need to replace (clients.id) with the client ID that you already have in your script and change speakers.id to whatever the ID field in your speakers table is called, and change field_with_speakers_list_string to whatever the field in your clients table with the string of speakers is called, and of course change the part of the SELECT to the fields you want to limit it by.

Answer 2

Based on the description of your database, each Client can have multiple Speakers. This is a one-to-many (1-N) relationship, and is typically expressed in two tables. One is a main table, "clients", which stores information about the client, but nothing about the speakers. A subordinate table, "speakers", stores information about each speaker AND the ID of the Client it is associated with.
For example, Speaker 1, Speaker 5, and Speaker 8 all have the same Client ID in the speakers table. The client_id field in the speakers table is called a foreign key.
Now you can get all the speaker information for Client 1 in one query:
select * from clients, speakers where clients.clientid=speakers.clientid and clients.clientid=1
Your current two-table design is flawed because you have the speakeridS column in the clients table. The foreign key column that expresses the ONE in a 1-N relationship should always be in the "many" table, i.e. "speakers".
Since your current speakers table doesn't have client_id information, you'll have to write a data transformer to migrate the string, comma-delimited speakers field in the clients table, to a numeric foreign key field "clientid" in the speakers table. This is a one-time transformation so you can do it in a PHP script:
$query="select * from clients";
$rs=mysql_query($query,$db);
while ($myrow=mysql_fetch_array($rs)){
$clientid=$myrow['clientid'];
$speakerids=explode(',',$myrow['speakers']);
foreach ($speakerids as $speakerid){
if (!is_numeric($speakerid)) continue;
$query="update speakers set clientid=$clientid where speakerid=$speakerid";
mysql_query($query,$db);
}
}
Your application displays the speakers in a checklist. The interface, however, doesn't have to dictate your storage structure. Write a loop and store the client ID in each speaker record.
IF the same speaker works with multiple clients, then you'll need a many-to-many (N-N) table. This is done via a bridging table. In this case, neither clients or speakers table need to know about each other. Create another table called "clientspeakers" which includes at least two foreign keys: clientid and speakerid.