如何连接所有表？

Question

I am a new programmer and I don't know how to do this.

I have:

• a table named customers (cust_id, name)
• a table named agents (agent_id, agent_name)
• a table named authorizations (cust_id, agent_id)
• a table named product_services (p_s_id, cust_id, agent_id, item_name, item_id)

About the authorizations table: the agent_id is the agent who the is authorised salesperson for cust_id . So, I need to be able to pull only results for this particular cust_id under this agent_id .

I need to do a query that will return all the products and services that the customer have under all other agents. In the search, it should also return products/services that they have under me as well.

This is what I have tried so far:

$sql = "SELECT 
          product_services.item_name, agents.agent_name,
          customers.name, agents.agent_id, product_services.item_id 
        FROM
          product_services 
        LEFT JOIN agents ON product_services.agent_id = agents.agent_id 
        LEFT JOIN customers ON product_services.cust_id = customers.cust_id 
        WHERE authorizations.agent_id = '$aid'
          AND  product_services.item_name LIKE '%$q%' 
        ORDER BY product_services.id DESC 
        LIMIT $start, $limit";

Answer 1

KPO,

Below is a query I used to connect 2 tables. It would be the same for your query, notice the syntax used starting at "LEFT JOIN"

    SELECT 
    user.username,
    groups.group_id, groups.group_name,  
    sign.last_connected, sign.sign_id, sign.sign_name, sign.resolution_x, sign.resolution_y, LEFT(sign.sign_name, 1) AS first_char
FROM
    user
LEFT JOIN(
    groups, sign
)ON(
    user.user_id = groups.userID AND
    groups.group_id = sign.groupID
)
WHERE
    username = ? AND
    UPPER(sign.sign_name) BETWEEN "A" AND "Z"
    OR sign.sign_name BETWEEN "0" AND "9" ORDER BY sign.sign_name

Considering your SQL query is initially correct this should work for your LEFT JOIN portion:

LEFT JOIN(agents, customers
)ON( product_services.agent_id = agents.agent_id 
AND product_services.cust_id = customers.cust_id) 

Answer 2

Typically, a query would start with the core table at the root of your criteria... Such as a single customer and join from that... You also state you want ALL products/services from ALL agents including the "me" agent, you would not want to have a filter on your '$aid' criteria.

SELECT STRAIGHT_JOIN 
      c.cust_id,
      c.name,
      ag.agent_id,
      ag.agent_name,
      ps.item_name,
      ps.p_s_id,
      ps.item_id
   from
      customers c
         join authorizations au
            on c.cust_id = au.cust_id
            [[ AND au.agent_id = '$aid' ]]
            join agents ag
               on au.agent_id = ag.agent_id
            join product_services ps
               on c.cust_id = ps.cust_id
              AND au.agent_id = ps.agent_id
              [[ AND ps.item_name like '%$q%' ]]
   order by
      ps.p_s_id DESC
   limit 
      $start, $limit

In the query above, I've put in section where you could apply your

[[ AND agent criteria ]]

or product/service criteria. But as you stated, you wanted ALL activity of ALL agents, so I've left it out... Likewise with a possible

[[ AND product / service ]] 

criteria which may/may not be provided and you can very simply strip it out...

-- EDIT PER COMMENT FEEDBACK.

As per your inquiry on how to add more "criteria", its based on the origin of the table. If its the FIRST table in the "FROM" clause, you'll add a WHERE clause and put criteria to that table... As for the others, like the agents and product services, where I had the [[ criteria ]], you could just expand your entire criteria there (per respective table its joined with).

Such as your [[ product service criteria ]], I could have added something like

AND (   (   ps.Item like '%$something'
         OR ps.Item like '%$another'
         OR ps.Item like '%$more' )
     AND ps.OtherField = whatever )

Keep your primary "join" conditions which identify the relationship between the tables first and foremost... only THEN do you want to add your restricting criteria... As you can see in my sample above, I've wrapped the entire AND ( ) clause within parenthesis to see it as a single "unit" condition... such as to the product/service table.

Hope this sample helps you in future querying.