Join 3 tables mysql php

Question

Im not sure on the terminology but i basically have a 2 table left join right now like this:

Snippets Table
snippet_id PK
snippet_text

snippets_link_email_id Table
snippet_id * (Links to Snippets Table)
email_id * (Links to emails Table)

emails Table
email_id 
version_no

lots of other various data

So whats happening is a log is parsed and inserted into the emails table, each record has details about the log text, the errors found and various information about the user.

The main info i need from each log is the error, each unique error is stored in the snippets Table.

Since there might be many emails with the same error i like to run the following query to see how many unique errors there were:

$total_exception_check = mysql_query("SELECT * FROM snippets");
$total_exceptions = mysql_num_rows($total_exception_check);

while ($row = mysql_fetch_array($total_exception_check))
{
$i = $row['snippet_id'];
//Need to find total occurrences of this error

$feedback_query = mysql_query("SELECT * FROM snippets LEFT JOIN snippets_link_email_id ON snippets.snippet_id = snippets_link_email_id.snippet_id WHERE snippets_link_email_id.snippet_id = $i AND snippet_date BETWEEN CURRENT_TIMESTAMP - INTERVAL '$num_days' HOUR AND CURRENT_TIMESTAMP");
}
$tot_snippets = mysql_num_rows($feedback_query);

So i basically loop through each unique error, then search the snippets_link_email_id Table to see how many times that error was recorded ie how many parsed emails had that error.

tot_snippets tells me the total amount of each. So this is great i can now build a table of each error and how many times it was recorded.

However in the emails table there is a lot of information including version number, what if i wanted to get total unique errors where the value of version_no in the emails table was = 2000

how would i edit this code to see that?

SELECT *
FROM snippets
LEFT JOIN snippets_link_email_id
    ON snippets.snippet_id = snippets_link_email_id.snippet_id
WHERE
    snippets_link_email_id.snippet_id = $i
    AND snippet_date BETWEEN
        CURRENT_TIMESTAMP - INTERVAL '$num_days' HOUR
        AND CURRENT_TIMESTAMP

I tried this from other similar posts but im guessing im miles off:

 SELECT *
 FROM snippets, emails
 LEFT JOIN snippets_link_email_id
     ON snippets.snippet_id = snippets_link_email_id.snippet_id
     AND snippets_link_email_id.email_id ON emails.email_id
 WHERE snippets_link_email_id.snippet_id = $i
 AND snippet_date BETWEEN
     CURRENT_TIMESTAMP - INTERVAL '$num_days' HOUR AND CURRENT_TIMESTAMP

Answer 1

The general form for joining multiple tables is

SELECT (columns or collations)
FROM table1
LEFT JOIN table2
ON (some condition that associates rows in table1 with rows in table2)
LEFT JOIN table3
ON (some condition that associates rows in table1 or table2 with rows in table3)
WHERE (whatever you want to limit the result set to)

The same basic pattern follows regardless how many tables you want to join, though if you're using a lot of tables then aliasing them might make your life a lot easier.

SELECT (columns or collations)
FROM table1 AS t1
LEFT JOIN table2 AS t2
ON (some condition that associates rows in t1 with rows in t2)
LEFT JOIN table3 AS t3
ON (some condition that associates rows in t1 or t2 with rows in t3)
WHERE (whatever you want to limit the result set to)

Answer 2

Will joining properly to email resolve it?

 SELECT *
 FROM snippets
 LEFT JOIN snippets_link_email_id
 ON snippets.snippet_id = snippets_link_email_id.snippet_id
 LEFT JOIN emails
 ON snippets_link_email_id.email_id = emails.email_id
 WHERE snippets_link_email_id.snippet_id = $i
 AND snippet_date BETWEEN CURRENT_TIMESTAMP - INTERVAL '$num_days' HOUR AND CURRENT_TIMESTAMP");

Also, I notice your very first query doesn't use a time stamp. That would return many more rows than you really need (I guess). You could filter that first query by timestamp, and then your loops would be substantially smaller:

SELECT * FROM snippets
     WHERE snippet_date BETWEEN CURRENT_TIMESTAMP - INTERVAL '$num_days' HOUR AND CURRENT_TIMESTAMP");