mySQL Left Join 5 Tables? - mysql

Question

Thanks in advance for any help. I am working with 5 tables in a mySQL database. The system is such that I have a top level table called "owners" (clients) that have local business (shops). These owners go out and create accounts at websites like yelp (citation_sources) and as such have login credential (citation_login). Once they have an account at a citation source, they add shops to the directory.
I am hoping to create one query that would select ALL of the citation sources, regardless of if an owner has an account or not, and loop through the recordset, showing login for each citation source they have an account with, as well as any shop listings.
My question pertains to doing a left join on 5 tables. I left out most fo the fields but have set up primary and foreign keys Is the sequence of the join important, ie. start with one particular table, ending with another?
I tried this command but it only brings back 33 rows when in fact there are 96 citation_sources.
I think I figured it out. I created a new table called "citation_shop" with a composite primary key - citation - shop. I then ran a query and it got me the results I was after. I ended up putting a condition in the first left join.
SELECT citation_sources.name, citation_shop.shop from citation_sources left join citation_shop on citation_sources.id = citation_shop.citation and citation_shop.shop in (6,7) left join shops on citation_shop.shop = shops.id group by citation_sources.name, citation_shop.shop limit 100
CREATE TABLE `citation_shop` (
`shop` smallint(5) UNSIGNED NOT NULL,
`citation` smallint(6) UNSIGNED NOT NULL,
`url` text NOT NULL,
`count` smallint(3) UNSIGNED NOT NULL,
`status` tinyint(1) UNSIGNED NOT NULL,
`sort` tinyint(3) UNSIGNED NOT NULL
) ENGINE=MyISAM DEFAULT CHARSET=utf8;
--
-- Indexes for dumped tables
--
--
-- Indexes for table `citation_shop`
--
ALTER TABLE `citation_shop`
ADD PRIMARY KEY (`citation`,`shop`);
select owners.id as owner_id, shops.id as shop_id, citation_sources.name, citation_shop_urls.url, citation_logins.password
from owners
inner join shops on owners.id = shops.owner_id
left join citation_logins on owners.id = citation_logins.owner
left join citation_sources on citation_logins.c_source = citation_sources.id
left join citation_shop_urls on citation_sources.id = citation_shop_urls.citation_id
where owners.id = 3
group by citation_sources.name
Here are my tables in order of what I think is relevlance:
CREATE TABLE `owners` (
`id` smallint(6) UNSIGNED NOT NULL,
) ENGINE=InnoDB DEFAULT CHARSET=utf8 ;
CREATE TABLE `shops` (
`id` smallint(5) UNSIGNED NOT NULL,
`title` varchar(50) DEFAULT '',
`owner_id` smallint(5) UNSIGNED NOT NULL,
) ENGINE=InnoDB DEFAULT CHARSET=utf8;
CREATE TABLE `citation_sources` (
`id` smallint(6) UNSIGNED NOT NULL,
) ENGINE=InnoDB DEFAULT CHARSET=utf8;
CREATE TABLE `citation_shop_urls` (
`shop` smallint(5) UNSIGNED NOT NULL DEFAULT '0',
`citation_id` tinyint(5) UNSIGNED NOT NULL DEFAULT '0',
`owner` smallint(6) NOT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8;
CREATE TABLE `citation_logins` (
`c_source` smallint(5) UNSIGNED NOT NULL DEFAULT '0',
`owner` smallint(6) NOT NULL,
`user_name` text NOT NULL,
`password` text NOT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

Answer 1

In a LEFT JOIN, the first table is the one where you get all the rows, even if they don't have a match in other tables. So if you want all citation_sources, even those not associated with any owner, then citation_sources should be the table on the left of the LEFT JOIN.
To filter the owner information only to id = 3, put o.id = 3 in the ON clause that joins with owners. Then use a WHERE clause to remove all the other rows.
SELECT o.id as owner_id, s.id as shop_id, cs.name, u.url, cl.password
FROM citation_sources AS cs
LEFT JOIN citation_shop_urls AS u ON u.citation_id = cs.id
LEFT JOIN citation_logins AS cl ON cs.id = cl.c_source
LEFT JOIN owners AS o ON o.id = cl.owner AND o.id = 3
LEFT JOIN shops AS s ON s.owner_id = o.id
WHERE o.id IS NULL OR o.id = 3