Advice on how to complete specific MySQL JOIN - mysql

I have a mysql table jobs.
This is the basic structure of jobs.
id
booked_user_id
assigned_user_id
I then also have another table, meta.
Meta has the structure:
id
user_id
first_name
last_name
Here is my php code
$sQuery = "
SELECT SQL_CALC_FOUND_ROWS job_id, job_name, priority_id, meta.first_name, date_booked
FROM jobs
LEFT JOIN (meta) on (meta.user_id = jobs.booked_user_id)
LEFT JOIN (jobs_priorities) on (jobs_priorities.id = jobs.priority_id)
$sWhere
$sOrder
$sLimit
";
$rResult = mysql_query($sQuery);
while ( $aRow = mysql_fetch_assoc( $rResult ) )
{
$sOutput .= '"'.addslashes($aRow['job_id']).'",';
}
How can I join these tables so that both booked_user_id and assigned_user_id can access meta.first_name?
When I try
$sOutput .= '"'.addslashes($aRow['first_name']).'",
nothing happens
Thanks for your advice
Tim

You can join twice:
SELECT j.id, b.first_name, a.first_name
FROM jobs j
JOIN meta b ON j.booked_user_id = b.user_id
JOIN meta a ON j.assigned_user_id = a.user_id

Nathan did the fix, but will apply it to your current SQL so you can understand it more
Lets transform your query into this:
SELECT SQL_CALC_FOUND_ROWS job_id, job_name, priority_id, date_booked
FROM jobs j
LEFT JOIN meta b ON b.user_id = j.booked_user_id
LEFT JOIN meta a ON a.user_id = j.assigned_user_id
LEFT JOIN jobs_priorities jp ON jp.id = j.priority_id
$sWhere
$sOrder
$sLimit
What I did is to use alias to method and join twice the meta, (just like what nathan did), I temporarily removed the first_name field,
Then let's add something on the SELECT so you can display both first_name
SELECT SQL_CALC_FOUND_ROWS job_id, job_name, priority_id, date_booked, b.first_name as booked_first_name, a.first_name as assigned_first_name
FROM jobs j
LEFT JOIN meta b ON b.user_id = j.booked_user_id
LEFT JOIN meta a ON a.user_id = j.assigned_user_id
LEFT JOIN jobs_priorities jp ON jp.id = j.priority_id
$sWhere
$sOrder
$sLimit
Now, we added the column booked_first_name and assigned_first_name, now you can call it on your php code like this:
$aRow['booked_first_name'] or $aRow['assigned_first_name']

Related

Mysql triple join error:Not unique table/alias: 'cushbu_mark_user_favorites'

I have 3 tables in my db
1)cushbu_users (id,first_name,last_name)
2)cushbu_art (id,user_id(FK cushbu_user),title,base_price etc...) -for store user arts
3)cushbu_mark_user_favorites (id,user_id(FK cushbu_user),art_id(FK cushbu_art)) -for marking favourite items
I want to fetch the all art items of a particular user favourited
with count of favourites each art (stored in cushbu_mark_usier_favorites table )
Here is my query
SELECT
cushbu_art.id AS art_id,
cushbu_art.title,
cushbu_art.base_price,
cushbu_art.image_name,
CONCAT(
cushbu_users.first_name,
' ',
cushbu_users.last_name
) AS artist_name,COUNT(cushbu_mark_user_favorites.art_id)
FROM
cushbu_art
JOIN cushbu_mark_user_favorites ON cushbu_mark_user_favorites.art_id = cushbu_art.id
JOIN cushbu_users ON cushbu_users.id = cushbu_art.artist_id
LEFT JOIN cushbu_mark_user_favorites ON cushbu_art.id=cushbu_mark_user_favorites.art_id
WHERE
cushbu_mark_user_favorites.user_id = 68
But i got Not unique table/alias: 'cushbu_mark_user_favorites' this join statement
LEFT JOIN cushbu_mark_user_favorites ON cushbu_art.id=cushbu_mark_user_favorites.art_id
UPDATE
SELECT
a.id AS art_id,
a.title,
a.base_price,
a.image_name,
CONCAT(
c.first_name,
' ',
c.last_name
) AS artist_name,COUNT(b.art_id)
FROM
cushbu_art a
JOIN cushbu_mark_user_favorites b ON b.art_id = a.id
JOIN cushbu_users c ON c.id = a.artist_id
LEFT JOIN b ON a.id=b.art_id
WHERE
b.user_id = 68
Try below query.
SELECT
cushbu_art.id AS art_id,
cushbu_art.title,
cushbu_art.image_name,
CONCAT(
cushbu_users.first_name,
' ',
cushbu_users.last_name
) AS artist_name , b.favorites_count as total_fav
FROM
cushbu_mark_user_favorites
LEFT JOIN cushbu_art ON cushbu_art.id=cushbu_mark_user_favorites.art_id
LEFT JOIN cushbu_users ON cushbu_users.id = cushbu_art.artist_id
LEFT JOIN (SELECT art_id,count(*) as favorites_count FROM cushbu_mark_user_favorites GROUP BY art_id) as b ON b.art_id=cushbu_art.id
WHERE cushbu_mark_user_favorites.user_id=1
GROUP BY cushbu_art.id
Hope this will helpful to you.

pdo add value to sql result

I use code below to get data from database
if( !empty( $books_ids ) )
{
$books_ids_in = implode(',', array_fill(0, count($books_ids), '?'));
$query = "SELECT
b.id,
b.`name`,
b.`year`,
GROUP_CONCAT(DISTINCT a.`name`) AS author_names,
GROUP_CONCAT(DISTINCT s.`name`) AS store_names
FROM
books AS b
LEFT JOIN books_authors AS b_a ON b.id = b_a.book_id
LEFT JOIN authors AS a ON a.id = b_a.author_id
LEFT JOIN books_stores AS b_s ON b.id = b_s.book_id
LEFT JOIN stores AS s ON s.id = b_s.store_id
WHERE
b.id IN (". $books_ids_in .")
GROUP BY b.id
ORDER BY b.id";
$stmt = $conn->prepare($query);
foreach ($books_ids as $k => $id) {
$stmt->bindValue(($k+1), $id);
}
$stmt->execute();
$results = $stmt->fetchAll();
}
and as I use $book id for this purpose, I would like to add some parameter in result to show that, for example, param = "book" for every row. Is there any way to do that?
Just pass it the string and alias it as a column. Though since you know the value passed in in code and display the values though code...... I'm not sure why you need this... as the value is available to you in the code when being displayed.
$query = "SELECT
b.id,
b.`name`,
b.`year`,
GROUP_CONCAT(DISTINCT a.`name`) AS author_names,
GROUP_CONCAT(DISTINCT s.`name`) AS store_names,
'". $param."' as forEveryRow
FROM
books AS b
LEFT JOIN books_authors AS b_a ON b.id = b_a.book_id
LEFT JOIN authors AS a ON a.id = b_a.author_id
LEFT JOIN books_stores AS b_s ON b.id = b_s.book_id
LEFT JOIN stores AS s ON s.id = b_s.store_id
WHERE
b.id IN (". $books_ids_in .")
GROUP BY b.id
ORDER BY b.id";

Combine query that relies on resultset of another

I run this query to get 20 random items from my wordpress database based on things like rating, category, etc
SELECT (A.user_votes/A.user_voters) as site_rating, B.ID as post_id, B.post_author, B.post_date,E.name as category
FROM `wp_gdsr_data_article` as A
INNER JOIN `wp_posts` as B ON (A.post_id = B.id)
INNER JOIN wp_term_relationships C ON (B.ID = C.object_id)
INNER JOIN wp_term_taxonomy D ON (C.term_taxonomy_id = D.term_taxonomy_id)
INNER JOIN wp_terms E ON (D.term_id = E.term_id)
WHERE
B.post_type = 'post' AND
B.post_status = 'publish' AND
D.taxonomy='category' AND
E.name NOT IN ('Satire', 'Declined', 'Outfits','Unorganized', 'AP')
ORDER BY RAND()
LIMIT 20
Then, for each result of the random items, I want to find a corresponding item that is very similar to the random item (around the same rating) but not identical and also one the user has not seen:
SELECT ABS($site_rating-(A.user_votes/A.user_voters)) as diff, (A.user_votes/A.user_voters) as site_rating, B.ID as post_id, B.post_author, B.post_date,E.name as category ,IFNULL(F.count,0) as count
FROM `wp_gdsr_data_article` as A
INNER JOIN `wp_posts` as B ON (A.post_id = B.id)
INNER JOIN wp_term_relationships C ON (B.ID = C.object_id)
INNER JOIN wp_term_taxonomy D ON (C.term_taxonomy_id = D.term_taxonomy_id)
INNER JOIN wp_terms E ON (D.term_id = E.term_id)
LEFT JOIN (
SELECT *,COUNT(*) as count FROM `verus` WHERE ip = '{$_SERVER['REMOTE_ADDR']}'
) as F ON (A.post_id = F.post_id_winner OR A.post_id = F.post_id_loser)
WHERE
E.name = '$category' AND
B.ID <> '$post_id' AND
B.post_type = 'post' AND
B.post_status = 'publish' AND
D.taxonomy='category' AND
E.name NOT IN ('Satire', 'Declined', 'Outfits','Unorganized', 'AP')
ORDER BY count ASC, diff ASC
LIMIT 1
Where the following php variables refer to the result of the previous query
$post_id = $result['post_id'];
$category = $result['category'];
$site_rating = $result['site_rating'];
and $_SERVER['REMOTE_ADDR'] refers to the user's IP.
Is there a way to combine the first query with the 20 additional queries that need to be called to find corresponding items, so that I need just 1 or 2 queries?
Edit: Here is the view that simplifies the joins
CREATE VIEW `versus_random` AS
SELECT (A.user_votes/A.user_voters) as site_rating, B.ID as post_id, B.post_author, B.post_date,E.name as category
FROM `wp_gdsr_data_article` as A
INNER JOIN `wp_posts` as B ON (A.post_id = B.id)
INNER JOIN wp_term_relationships C ON (B.ID = C.object_id)
INNER JOIN wp_term_taxonomy D ON (C.term_taxonomy_id = D.term_taxonomy_id)
INNER JOIN wp_terms E ON (D.term_id = E.term_id)
WHERE
B.post_type = 'post' AND
B.post_status = 'publish' AND
D.taxonomy='category' AND
E.name NOT IN ('Satire', 'Declined', 'Outfits','Unorganized', 'AP')
My attempt now with the view:
SELECT post_id,
(
SELECT INNER_TABLE.post_id
FROM `versus_random` as INNER_TABLE
WHERE
INNER_TABLE.post_id <> OUTER_TABLE.post_id
ORDER BY (SELECT COUNT(*) FROM `versus` WHERE ip = '54' AND (INNER_TABLE.post_id = post_id_winner OR INNER_TABLE.post_id = post_id_loser)) ASC
LIMIT 1
) as innerquery
FROM `versus_random` as OUTER_TABLE
ORDER BY RAND()
LIMIT 20
However the query just timesout and freezes my mysql.
I think it should work like this, but I don't have any Wordpress at hand to test it. The second query that gets the related post is embedded in the other query, when it gets just the related_post_id. The whole query is turned into a subquery itself, given the alias 'X' (although you are free to use 'G', if you want to continue your alphabet.)
In the outer query, the tables for posts and data-article are joined again (RA and RP) to query the relevant fields of the related post, based on the related_post_id from the inner query. These two tables are left joined (and in reverse order), so you still get the main post if no related post was found.
SELECT
X.site_rating,
X.post_id,
X.post_author,
X.post_date,
X.category,
RA.user_votes / RA.user_voters as related_post_site_rating,
RP.ID as related_post_id,
RP.post_author as related_post_author,
RP.post_date as related_post_date,
RP.name as related_category,
FROM
( SELECT
(A.user_votes/A.user_voters) as site_rating,
B.ID as post_id, B.post_author, B.post_date,E.name as category,
( SELECT
RB.ID as post_id
FROM `wp_gdsr_data_article` as RA
INNER JOIN `wp_posts` as RB ON (RA.post_id = RB.id)
INNER JOIN wp_term_relationships RC ON (RB.ID = RC.object_id)
INNER JOIN wp_term_taxonomy RD ON (RC.term_taxonomy_id = RD.term_taxonomy_id)
INNER JOIN wp_terms RE ON (RD.term_id = RE.term_id)
LEFT JOIN (
SELECT *,COUNT(*) as count FROM `verus` WHERE ip = '{$_SERVER['REMOTE_ADDR']}'
) as RF ON (RA.post_id = RF.post_id_winner OR RA.post_id = RF.post_id_loser)
WHERE
RE.name = E.name AND
RB.ID <> B.ID AND
RB.post_type = 'post' AND
RB.post_status = 'publish' AND
RD.taxonomy='category' AND
RE.name NOT IN ('Satire', 'Declined', 'Outfits','Unorganized', 'AP')
ORDER BY count ASC, diff ASC
LIMIT 1) as related_post_id
FROM `wp_gdsr_data_article` as A
INNER JOIN `wp_posts` as B ON (A.post_id = B.id)
INNER JOIN wp_term_relationships C ON (B.ID = C.object_id)
INNER JOIN wp_term_taxonomy D ON (C.term_taxonomy_id = D.term_taxonomy_id)
INNER JOIN wp_terms E ON (D.term_id = E.term_id)
WHERE
B.post_type = 'post' AND
B.post_status = 'publish' AND
D.taxonomy='category' AND
E.name NOT IN ('Satire', 'Declined', 'Outfits','Unorganized', 'AP')
ORDER BY RAND()
LIMIT 20
) X
LEFT JOIN `wp_posts` as RP ON RP.id = X.related_post_id
LEFT JOIN `wp_gdsr_data_article` as RA.post_id = RP.id
I can't test my proposal so take it with the benefit of the doubt. Anyway i hope it could be a valid starting point for some of the issues faced.
I can not imagine a solution that does not pass through a temporary table, cabling onerous computations present in your queries. You could also have the goal to not interfere with the randomization of the first phase. In the following I try to clarify.
I'll start with these rewritings:
-- first query
SELECT site_rating, post_id, post_author, post_date, category
FROM POSTS_COMMON
ORDER BY RAND()
LIMIT 20
-- second query
SELECT ABS(R.site_rating_A - R.site_rating_B) as diff, R.site_rating_B as site_rating, P.post_id, P.post_author, P.post_date, P.category, F.count
FROM POSTS_COMMON AS P
INNER JOIN POSTS_RATING_DIFFS AS R ON (P.post_id = R.post_id_B)
LEFT JOIN (
/* post_id_winner, post_id_loser explicited; COUNT(*) NULL treatment anticipated */
SELECT post_id_winner, post_id_loser, IFNULL(COUNT(*), 0) as count FROM `verus` WHERE ip = '{$_SERVER['REMOTE_ADDR']}'
) as F ON (P.post_id = F.post_id_winner OR P.post_id = F.post_id_loser)
WHERE
P.category = '$category'
AND R.post_id_A = '$post_id'
ORDER BY count ASC, diff ASC
LIMIT 1
with:
SELECT A.post_id_A, B.post_id_B, A.site_rating as site_rating_A, B.site_rating as site_rating_B
INTO POSTS_RATING_DIFFS
FROM POSTS_COMMON as A, POSTS_COMMON as B
WHERE A.post_id <> B.post_id AND A.category = B.category
CREATE VIEW POSTS_COMMON AS
SELECT A.ID as post_id, A.user_votes, A.user_voters, (A.user_votes / A.user_voters) as site_rating, B.post_author, B.post_date, E.name as category
FROM wp_gdsr_data_article` as A
INNER JOIN `wp_posts` as B ON (A.post_id = B.post_id)
INNER JOIN wp_term_relationships C ON (B.ID = C.object_id)
INNER JOIN wp_term_taxonomy D ON (C.term_taxonomy_id = D.term_taxonomy_id)
INNER JOIN wp_terms E ON (D.term_id = E.term_id)
WHERE
B.post_type = 'post' AND
B.post_status = 'publish' AND
D.taxonomy='category' AND
E.name NOT IN ('Satire', 'Declined', 'Outfits','Unorganized', 'AP')
POSTS_COMMON isolates a common view between the two queries.
With POSTS_RATING_DIFFS, a temporary table populated with the ratings combinations and diffs, we have "the trick" of transforming the inequality join criteria on post_id(s) in an equality one (see R.post_id_A = '$post_id' in the second query).
We also take advantage of a temporary table in having precomputed ratings for the combinatory explosion of A.post_id <> B.post_id (with post category equality), and moreover being useful for other sessions.
Also extracting the RAND() ordering in a temporary table could be advantageous. In this case we could limit the ratings combinations and diffs only on the 20 randomly chosen.
Original limiting to one single row in the dependent second level query is done by mean of ordering and limit statements.
The proposed solution avoids elaborating a LIMIT 1 on an ORDER BY resultset in the second level query wich become a subquery.
The single row calculation in the subquery is done by mean of a WHERE criteria on the maximum of a single value calculated from the columns values on which ORDER BY clause is used.
The combination into a single value must be valid in preserving the correct ordering. I'll leave in pseudo-code as:
'<combination of count and diff>'
For example, using combination of the two values into a string type, we could have:
CONCAT(LPAD(CAST(count AS CHAR), 10, '0'), LPAD(CAST(ABS(diff) AS CHAR), 20, '0'))
The structure of the single query would be:
SELECT (Q_LVL_1.user_votes/Q_LVL_1.user_voters) as site_rating_LVL_1, Q_LVL_1.post_id as post_id_LVL_1
, Q_LVL_1.post_author as post_author_LVL_1, Q_LVL_1.post_date as post_date_LVL_1
, Q_LVL_1.category as category_LVL_1, Q_LVL_2.post_id as post_id_LVL_2
, Q_LVL_2.diff as diff_LVL_2, Q_LVL_2.site_rating as site_rating_LVL_2
, Q_LVL_2.post_author as post_author_LVL_2, Q_LVL_2.post_date as post_date_LVL_2
, Q_LVL_2.count
FROM POSTS_COMMON AS Q_LVL_1
, /* 1-row-selection query placed side by side for each Q_LVL_1's row */
(
SELECT CORE_P.post_id, CORE_P.ABS_diff as diff, P.site_rating, P.post_author, P.post_date, CORE_P.count
FROM POSTS_COMMON AS P
INNER JOIN (
SELECT FIRST(CORE_P.post_id) as post_id, ABS(CORE_P.diff) as ABS_diff, CORE_P.count
FROM (
/*
selection of posts with post_id(s) different from first level query,
not already taken and with the topmost value of
'<combination of count and diff>'
*/
) AS CORE_P
GROUP BY CORE_P.count, ABS(CORE_P.diff)
/* the one row selector */
) AS CORE_ONE_LINER ON P.post_id = CORE_ONE_LINER.post_id
) AS Q_LVL_2
ORDER BY RAND()
LIMIT 20
CORE_P selection could have more post_id(s) corresponding to the topmost value '<combination of count and diff>', so the use of GROUP BY and FIRST clauses to reach the single row.
This brings to a possible final implementation:
SELECT (Q_LVL_1.user_votes/Q_LVL_1.user_voters) as site_rating_LVL_1, Q_LVL_1.post_id as post_id_LVL_1
, Q_LVL_1.post_author as post_author_LVL_1, Q_LVL_1.post_date as post_date_LVL_1
, Q_LVL_1.category as category_LVL_1, Q_LVL_2.post_id as post_id_LVL_2
, Q_LVL_2.diff as diff_LVL_2, Q_LVL_2.site_rating as site_rating_LVL_2
, Q_LVL_2.post_author as post_author_LVL_2, Q_LVL_2.post_date as post_date_LVL_2
, Q_LVL_2.count
FROM POSTS_COMMON AS Q_LVL_1
, (
SELECT CORE_P.post_id, CORE_P.ABS_diff as diff, P.site_rating, P.post_author, P.post_date, CORE_P.count
FROM POSTS_COMMON AS P
INNER JOIN
(
SELECT FIRST(CORE_P.post_id) as post_id, ABS(CORE_P.diff) as ABS_diff, CORE_F.count
FROM (
SELECT CORE_RATING.post_id as post_id, ABS(CORE_RATING.diff) as ABS_diff, CORE_F.count
FROM (
SELECT post_id_B as post_id, site_rating_A - site_rating_B as diff
FROM POSTS_RATING_DIFFS
WHERE POSTS_RATING_DIFFS.post_id_A = Q_LVL_1.post_id
) as CORE_RATING
LEFT JOIN (
SELECT post_id_winner, post_id_loser, IFNULL(COUNT(*), 0) as count
FROM `verus`
WHERE ip = '{$_SERVER['REMOTE_ADDR']}'
) as CORE_F ON (CORE_RATING.post_id = CORE_F.post_id_winner OR CORE_RATING.post_id = CORE_F.post_id_loser)
WHERE
POSTS_RATING_DIFFS.post_id_A = Q_LVL_1.post_id
AND '<combination of CORE_F.count and CORE_RATING.diff>'
= MAX (
SELECT '<combination of CORE_F_2.count and CORE_RATING_2.diff>'
FROM (
SELECT site_rating_A - site_rating_B as diff
FROM POSTS_RATING_DIFFS
WHERE POSTS_RATING_DIFFS.post_id_A = Q_LVL_1.post_id
) as CORE_RATING_2
LEFT JOIN (
SELECT post_id_winner, post_id_loser, IFNULL(COUNT(*), 0) as count
FROM `verus`
WHERE ip = '{$_SERVER['REMOTE_ADDR']}'
) as CORE_F_2 ON (CORE_RATING_2.post_id = CORE_F_2.post_id_winner OR CORE_RATING_2.post_id = CORE_F_2.post_id_loser)
) /* END MAX */
) AS CORE_P
GROUP BY CORE_P.count, ABS(CORE_P.diff)
) AS CORE_ONE_LINER ON P.post_id = CORE_ONE_LINER.post_id
) AS Q_LVL_2
ORDER BY RAND()
LIMIT 20

mysql syntax how to add a third table to $query

I have code:
$query = "SELECT a.*, c.name as categoryname, c.id as categoryid
FROM #__table_one as a
LEFT JOIN #__table_two c ON c.id = a.catid";
$query .= " WHERE a.published = 1
AND a.access <= {$aid}
AND a.trash = 0
AND c.published =
AND c.access <= {$aid}
AND c.trash = 0";
I would like to add a third table ('__some_table') for the parts of the query where a.publish, a.access and a.trash. In other words, I want these fields to be retrieved from another table, not "#__table_one", but I do not know how to incorporate the #__some_table into the current query
I imagine the JOIN command can help me, but I do not know how to code mysql
//not tested
$query = "SELECT a.*, c.name as categoryname, c.id as categoryid
FROM #__table_one as a
LEFT JOIN #__table_two c ON c.id = a.catid
LEFT JOIN #__table_three d ON d.id = a.some_id";

MySQL: "Ignore" if a table row is missing during JOIN

I'm doing a LEFT JOIN on three tables, where the table "time" doesn't necessarily contain any matching rows. But if no matching rows is found in that table, the linked data disappears.
SELECT
w.date AS worker_date,
w.name AS worker_name,
w.address AS worker_address,
w.zip AS worker_zip,
w.place AS worker_place,
w.phone AS worker_phone,
w.email AS worker_email,
w.company AS worker_company,
w.accessibility AS worker_accessibility,
c.date AS client_date,
c.name AS client_name,
c.address AS client_address,
c.zip AS client_zip,
c.place AS client_place,
c.phone AS client_phone,
c.email AS client_email,
c.web AS client_web,
c.contact AS client_contact,
j.date AS job_date,
j.client_id,
j.worker_id,
j.name AS job_name,
j.description AS job_description,
j.type AS job_type,
j.status AS job_status,
j.proof AS job_proof,
j.deadline AS job_deadline,
j.price AS job_price,
j.final_client AS job_final_client,
SUM(t.hours) AS time_hours
FROM
jobs AS j
LEFT JOIN (
workers AS w,
clients AS c,
time AS t
) ON (
w.id = j.worker_id AND
c.id = j.client_id AND
j.id = t.job_id
) GROUP BY
j.id;
How can I make this work?
Thank you in advance.
add
WHERE t.job_id IS NOT NULL before GROUP BY
Try Replace
SUM(t.hours) AS time_hours
to
(SELECT IFNULL(SUM(t.hours),0) FROM time WHERE time.job_id=j.job_id) AS time_hours
And remove the time from the join
I think your basic query is correct (with the join under braces)
Just replace
SUM(t.hours) AS time_hours
with
SUM(if(t.hours is NULL,0,t.hours)) AS time_hours
I am not sure if this is the problem here, but the behavior of commas vs JOINs changed after a certain MySQL version. Try this
...
FROM jobs AS j LEFT JOIN workers AS w ON w.id = j.worker_id
LEFT JOIN clients AS c c.id = j.client_id
LEFT JOIN `time` AS t ON j.id = t.job_id
...
Also modify the SUM with IFNULL as #ajreal suggests.