有关子查询和表联接的SQL帮助

Question

Need some sql help...using MYSQL...I've got some legacy code and a situation to resolve...This code below only returns occupants who have a record in the p_occupants_insurance table. I want to be able to list all the occupants regardless if they have a record in the p_occupants_insurance table or not.

    SELECT a.occupants_insurance_id, a.occupant_id, a.policy_nbr, a.policy_type, a.coverage_amount_curr,

    CASE
        WHEN a.effective_date = '0000-00-00' THEN NULL
        ELSE a.effective_date
    END as effective_date,

    CASE
        WHEN a.expiration_date = '0000-00-00' THEN NULL
        ELSE a.expiration_date
    END as expiration_date,

a.insurance_company, a.custom1_label, a.custom2_label, a.custom3_label, a.custom1, a.custom2, a.custom3, c.name as prop_name, (SELECT x.name FROM portfolio_hierarchy x WHERE x.leaf_node_portf_id = d.portfolio_id ) as p_name, b.name as occupant_name, b.primary_contact, b.phone
FROM p_occupants_insurance a, p_occupants b, properties c, portfolio d
WHERE a.occupant_id = b.occupant_id
AND b.property_id = c.properties_id
AND c.portfolio_id = d.portfolio_id
AND d.account_id = 1
AND b.archived = 0
AND b.trashbin = 0
ORDER BY d.p_name ASC, prop_name ASC, occupant_name ASC, insurance_company ASC, policy_nbr ASC;

I know I can do subqueries like this:

SELECT b.name as occupant_name, b.primary_contact, b.phone,

(SELECT a.occupants_insurance_id FROM p_occupants_insurance a WHERE a.occupants_id = b.occupants_id) as occupants_insurance_id 


    FROM p_occupants b, properties c, portfolio d
    WHERE a.occupant_id = b.occupant_id
    AND b.property_id = c.properties_id
    AND c.portfolio_id = d.portfolio_id
    AND d.account_id = 1
    AND b.archived = 0
    AND b.trashbin = 0
    ORDER BY d.p_name ASC, prop_name ASC, occupant_name ASC, insurance_company ASC, policy_nbr ASC;

But that is going to lead to a subquery for each column I want out of the p_occupants_insurance table. Is there a better way to accomplish this and can you help me write out the SQL? Sorry, SQL is not my strongest point.

Thanks for the help.

Answer 1

Without seeing the schema for each of the tables involved, and relying only on the sample SQL statement, it is difficult to say for sure, but I believe the following will return the result you are looking for:

 SELECT 
    a.`occupants_insurance_id`,
    a.`occupant_id`,
    a.`policy_nbr`,
    a.`policy_type`,
    a.`coverage_amount_curr`,
    IF(a.`effective_date` = '0000-00-00',NULL,a.`effective_date`) as a.`effective_date`,
    IF(a.`expiration_date` = '0000-00-00',NULL,a.`expiration_date`) as a.`expiration_date`,
    a.`insurance_company`,
    a.`custom1_label`,
    a.`custom2_label`,
    a.`custom3_label`,
    a.`custom1`,
    a.`custom2`,
    a.`custom3`,
    c.`name` as `prop_name`, 
    (SELECT x.name FROM portfolio_hierarchy x WHERE x.leaf_node_portf_id = d.portfolio_id ) as `p_name`,
    b.`name` as `occupant_name`,
    b.`primary_contact`,
    b.`phone`
FROM `p_occupants` b
LEFT JOIN `p_occupants_insurance` a
    ON a.`occupant_id` = b.`occupant_id`
JOIN `properties` c
    ON b.`property_id` = c.`properties_id`
JOIN `portfolio` d
    ON c.`portfolio_id` = d.`portfolio_id`
WHERE d.account_id = 1
    AND b.archived = 0
    AND b.trashbin = 0
ORDER BY d.p_name ASC, 
    `prop_name` ASC, 
    `occupant_name` ASC, 
    `insurance_company` ASC, 
    `policy_nbr` ASC;