根据结果​​中一列的内容生成一个动态选择INNER JOIN的SQL语句

Question

I have the following SQL query:

$sql =  "
    SELECT
        id,
        refid,
        action_id,
        action_type,
        co_user_id,
        cust_vend_id,
        cust_vend_type,
        Aes_decrypt(cust_vend_name, '".DBKEY."') AS cust_vend_name,
        Aes_decrypt(amount, '".DBKEY."')         AS amount,
        Aes_decrypt(action_date, '".DBKEY."')   AS action_date,
        Aes_decrypt(memo, '".DBKEY."')         AS memo,
        Aes_decrypt(trans_id, '".DBKEY."')     AS trans_id,
        entry_datetime,
        part_id,
        polarity
    FROM
        generated_actions
    WHERE  acc_type = 1
        AND acc_id = $ref_id
        AND action_type != 2
        AND reverse_id IS NULL
    ORDER BY generated_actions.action_id DESC ";

It works, but I need to add an INNER JOIN ON either customers or vendors depending on whether the contents of cust_vend_type column is a '1' (customers) or '2' (vendors) and then grab customers_comp_name if '1' or `vendors_comp_name' if '2'.

Looking forward to choosing the best solution or marking up helpful advice!

UPDATE

This is the code updated with @ciaran's response below. The problem is that it seems to be returning an empty resultset even though I know there are qualified records.

$sql =  "
    SELECT
        ga.id,
        ga.refid,
        ga.action_id,
        ga.action_type,
        ga.co_user_id,
        ga.cust_vend_id,
        ga.cust_vend_type,
        Aes_decrypt(ga.amount, '".DBKEY."')                 AS amount,
        Aes_decrypt(ga.action_date, '".DBKEY."')            AS action_date,
        Aes_decrypt(ga.memo, '".DBKEY."')                   AS memo,
        Aes_decrypt(ga.trans_id, '".DBKEY."')               AS trans_id,
        ga.entry_datetime,
        ga.part_id,
        ga.polarity,
    SELECT CASE
        WHEN
            ga.cust_vend_type IS NULL
        THEN
            NULL
        WHEN
            ga.cust_vend_type = '1'
        THEN
            AES_DECRYPT(c.cust_comp_name, '".DBKEY."')
        ELSE
            AES_DECRYPT(v.vendor_comp_name, '".DBKEY."') END AS cust_vend_name
        FROM
            generated_actions ga
        LEFT OUTER JOIN
            customers c
        ON
            c.cust_id = ga.cust_vend_id
        LEFT OUTER JOIN
            vendors v
        ON
            v.vendor_id = ga.cust_vend_id
        WHERE
            ga.acc_type = 1
        AND
            ga.acc_id = $ref_id
        AND
            ga.action_type != 2
        AND
            ga.reverse_id IS NULL
        ORDER BY
            ga.action_id DESC ";

Not sure what I've done wrong?

Answer 1

You need an outer join and then use an CASE (or IF) to select the correct name...

SELECT CASE WHEN generated_actions.cust_vend_type Is Null Then Null 
            WHEN generated_actions.cust_vend_type = '1'
            THEN customers.customers_comp_name
            ELSE vendors.vendors_comp_name END as Cust_Vend_Name

  FROM generated_actions

       LEFT OUTER JOIN customers ON customers.id=generated_actions.cust_vend_id
       LEFT OUTER JOIN vendors ON vendors.id=generated_actions.cust_vend_id

i.e. your query should read...

$sql =  "
    SELECT
        ga.id,
        ga.refid,
        ga.action_id,
        ga.action_type,
        ga.co_user_id,
        ga.cust_vend_id,
        ga.cust_vend_type,
        Aes_decrypt(ga.amount, '".DBKEY."')                 AS amount,
        Aes_decrypt(ga.action_date, '".DBKEY."')            AS action_date,
        Aes_decrypt(ga.memo, '".DBKEY."')                   AS memo,
        Aes_decrypt(ga.trans_id, '".DBKEY."')               AS trans_id,
        ga.entry_datetime,
        ga.part_id,
        ga.polarity,
        CASE WHEN ga.cust_vend_type IS NULL THEN NULL
             WHEN ga.cust_vend_type = '1' THEN AES_DECRYPT(c.cust_comp_name, '".DBKEY."')
             ELSE AES_DECRYPT(v.vendor_comp_name, '".DBKEY."') END AS cust_vend_name
   FROM generated_actions ga
        LEFT OUTER JOIN customers c ON c.cust_id = ga.cust_vend_id
        LEFT OUTER JOIN vendors v ON ga.cust_vend_id
  WHERE ga.acc_type = 1
    AND ga.acc_id = $ref_id
    AND ga.action_type != 2
    AND ga.reverse_id IS NULL
  ORDER BY ga.action_id DESC ";