What would anyone think of this query ?
SELECT * FROM ta LEFT JOIN
(SELECT * FROM tb WHERE tb.end > 10000) AS tb
ON ta.id = tb.id
Is it ok to use table name ("tb") as alias or are there some invisible consequences ?
Reason: I have static methods to map ResultSet to object which use table name prefix. Would be nice to leave these methods alone.
Yes, you can use any alias, as long as the alias doesn't conflict with other aliases (tables without alias are give an alias with their name). This applies to a single query scope. In your query you have 2 scopes: one for the outer query and one for the inner query, thus you should not have a conflict even the same alias appears in both scopes.
Your query looks fine but why don't you use a simple LEFT JOIN
SELECT ta.*
FROM ta
LEFT JOIN tb ON ta.id = tb.id
WHERE tb.end > 10000
Yes it is perfectly fine to use the alias name as the table name.
Related
I have 2 tables:
table 1:userdetails with fields:uid,mobile,name
table 2:accountdetails with fields:uid,savings,balance
Where uid is common and primary key in both tables.
Now Iam trying to get mobile,savings values from both tables where uid =1 how can we get.I tried below but didnt worked.
select mobile,savings
from userdetails,accountdetails
where userdetails.uid='1'AND
userdetails.uid = accountdetails.uid
Please can some one help
More modern version using the JOIN syntax:
SELECT
a.`mobile`,
b.`savings`
FROM `userdetails` a
JOIN `accountdetails` b
ON a.`uid` = b.`uid`
WHERE a.`uid` = 1
The query should probably look like this:
select ud.mobile, ad.savings
from userdetails ud left join
accountdetails ad
on ud.uid = ad.uid
where ud.uid = 1;
Notes:
Use proper, explicit JOIN syntax.
Use meaningful table aliases and qualify all columns names.
The left join keeps all rows, even if there is no match in the second table. That might be your problem.
I am assuming that uid is actually a number. Don't put numbers around numeric constants.
You could turn on your error display to show you exactly what line is causing the issue.
ini_set('display_errors', 1);
You can try this.
SELECT `ud`.`mobile`, `ad`.`savings`
FROM `userdetails` `ud`
INNER JOIN `accountdetails` `ad` ON `ud`.`uid` = `ad`.`uid`
WHERE `us`.`uid` = 1
Use join
select mobile,savings
from userdetails join accountdetails on userdetails.uid = accountdetails.uid
where userdetails.uid='1'
I have a query which looks like this
$db->query("SELECT A.page_id, A.page_name FROM user_likes_pages as A , user_likes as B WHERE A.page_id = B.page_id AND B.country_id = ".$user_reg." ");
The thing is, I want to select a column from user_likes. Do I have to make a join or I can do it in different way. Thank you.
You have a join in your query, but it is implicit. You should write the query as:
SELECT ulp.page_id, ulp.page_name, ul.<whatever>
FROM user_likes ul JOIN
user_likes_pages ulp
ON ul.page_id = ulp.page_id
WHERE ul.country_id = ".$user_reg."
In addition to adding the explicit join syntax, I also changed the table aliases so they are abbreviations of the table name. This makes it easier to read the query and avoid mistakes.
You select B.columnname. You don't need a join, because you have the A.page_id = B.page_id.
I'm a new code having trouble getting a subquery to work with the main query data. Essentially I want to count how many PCs are HP PCs from the results. When I run it I get the error: The multi-part identifier "dbo.softwareapplications.softwareid" could not be bound.
select distinct appname, version, linkid,
(select count(make) as totalhp from dbo.workstations where make = 'Hewlett-Packard' and linkdid = t1.linkid)as totalhp
from dbo.softwareapplications as t1
join dbo.assignments on dbo.softwareapplications.softwareid = dbo.IQCSassignments.softwareid
join dbo.workstations on dbo.assignments.wsid = dbo.workstations.wsid
group by assetdescription, version, linkid, totalhp
Any help would be appreciated.
Since you've aliased the "dbo.softwareapplications" table as t1, that's how you have to refer to it in subsequent clauses:
join dbo.assignments on t1.softwareid = dbo.IQCSassignments.softwareid
(Or alternatively, remove the "as t1" alias and the other reference to it.)
Use the alias you created : t1.softwareid instead of dbo.softwareapplications.softwareid
Let's say I have two tables, and both their primary identifiers use the name 'id'. If I want to perform a join with these two tables, how would I alias the id of the table that I want to join with the former table?
For example:
SELECT * FROM `sites_indexed` LEFT JOIN `individual_data` ON `sites_indexed`.`id` = `individual_data`.`site_id` WHERE `url` LIKE :url
Now, site_id is supposed to link up with sites_indexed.id. The actual id which represents the row for individual_data however has the same title as sites_indexed.
Personally, I like to just use the name id for everything, as it keeps things consistent. When scripting server-side however, it can make things confusing.
e.g.
$var = $result['id'];
Given the aforementioned query, wouldn't this confuse the interpreter?
Anyway, how is this accomplished?
Instead of selecting all fields with "SELECT *" you should explicitly name each field you need, aliasing them with AS as required. For example:
SELECT si.field1 as si_field1,
si.field2 as si_field2,
ind_data.field1 as ind_data_field1
FROM sites_indexed as si
LEFT JOIN individual_data as ind_data
ON si.id = ind_data.site_id
WHERE `url` LIKE :url
And then you can reference the aliased names in your result set.
This thread is old and i found because i had the same problem. Now i have a better solution.
The answer given by Paul McNett and antun forces you to list all fields but in some cases this is impossible (too much fields to list), so you can keep the * and alias only the fields you want (typically the fields that have the same name and will override each other).
Here's how :
SELECT *, t.myfield as myNewName
FROM table t ... continue your query
you can add as much aliases as you want by adding comas.
Using this expression you will get results with columns id (from table sites_indexed) and id2 (alias for column id from table individual_data)
SELECT t1 . *, t2 . * FROM sites_indexed t1
LEFT JOIN (select id as id2, other_field1, other_field2 FROM individual_data) t2 ON t1.id = t2.site_id WHERE your_statement
The problem is that you're using the * wildcard. If you explicitly list the column names in your query, you can give them aliases:
SELECT `sites_indexed`.`id` AS `sites_indexed_id`,
`individual_data`.`id` AS `individual_data_id`
FROM `sites_indexed`
LEFT JOIN `individual_data` ON `sites_indexed`.`id` = `individual_data`.`site_id`
WHERE `url` LIKE :url
Then you can reference them via the alias:
$var = $result['sites_indexed_id'];
$var_b = $result['individual_data_id'];
I'm trying to use the following query, and if it only has one having statement it works as expected. If I add the second having statement it does not work.
SELECT candidate.first_name,
candidate.last_name,
qualification.code,
property.value AS funding_band_value,
qualification.funding_band,
property.value AS qualification_level_value,
qualification.qualification_level_id
FROM candidate_qualification, candidate, qualification, property
WHERE candidate_qualification.candidate_id=candidate.id and
candidate_qualification.qualification_id=qualification.id
HAVING funding_band_value = (select property.value from property where qualification.funding_band=property.id) and
HAVING qualification_level_value = (select property.value from property where qualification.qualification_level_id=property.id)
Could someone explain why this doesn't work and how I should do this.
HAVING acts similarly to WHERE or GROUP BY. You reference it once to start using it and combine multiple statements with AND or OR operators. An in depth look at the query parser might give you a more explicit answer.
You don't need HAVING here, just use AND so it is part of your WHERE clause.
The subqueries are not necessary, those tables are already joined.
Something like this should be closer to what you want:
SELECT c.first_name,
c.last_name,
q.code,
p.value AS funding_band_value,
q.funding_band,
p.value AS qualification_level_value,
q.qualification_level_id
FROM candidate_qualification cq
INNER JOIN candidate c ON cq.candidate_id=c.id
INNER JOIN qualification q ON cq.qualification_id=q.id
INNER JOIN property p ON q.funding_band=p.id
and q.qualification_level_id=p.id