How to limit query to 100 if i have selected data from two tables.
But i want the limit 100 to only work on one of them.
SELECT c.* , p.*
FROM test c,test2 p
WHERE c.id=p.id_puf
LIMIT 100
But here is the tricky part(at least for me)
In table "test" ja hold names.
Structure:
ID, Name, Age
Table "test2" ja hold record of the persons and they are connected with user ID
Structure:
ID, connect(this is same as "test" id), numbers
Now every tabel row in "test" is unique
I want to get all the results for test but all the record from the "test2".
Here is how you would do it -- select the items from the first table you want and then join to the 2nd table.
SELECT *
FROM (
SELECT *
FROM test
LIMIT 100
) c
LEFT JOIN test2 p ON c.id=p.id_puf
Notice I'm using "modern" joins. The join style you were using is about 20 years out of date and is not as good. It is much clearer how to solve this problem if you are using modern joins (for example).
Related
I'm having some problems retrieving data from two tables and then listing them. I'd like to list the user's feed posts and their likes activity all in one.
Feeds - Table for users posts
Likes - Table for users likes (So when a use likes a post, a record is added to likes (Table likes contains data which contains the feeds ID of the post liked)
What I'm attempting to make: List BOTH feeds and user's Like activity in an ACTIVITY WALL.
So it should output like (ordered by timestamp desc):
"THIS IS A POST by user A"
Shows that user C liked user B's post
"THIS IS A POST by user B"
"THIS IS A POST by user L"
Shows that user A liked user F's post
"THIS IS A POST by user F"
-and it goes on-
My current SQL:
SELECT * FROM feeds,likes WHERE feeds.deleted!=0 or likes.deleted!=0 ORDER BY feeds.timestamp, likes.timestamp
However, my problem is I have no idea how to link both tables, since the IDs in my 'feeds' differ from those in 'likes'
To combine the two sets, you can use a UNION ALL set operator.
Something like this:
SELECT f.timestamp AS `timestamp`
, 'feed' AS `src`
, f.feed_id AS `id`
, f.feed_content AS `content`
FROM feeds f
WHERE f.deleted!=0
UNION ALL
SELECT l.timestamp AS `timestamp`
, 'like' AS `src`
, l.like_id AS `id`
, l.note AS `content`
FROM likes l
WHERE l.deleted!=0
ORDER BY 1 DESC
Note the the queries (on either side of the UNION ALL operator) need to match, in terms of the number of columns returned, and the datatype of each column.
To accommodate differences, such as extra columns returned from one table, but not from the other, you can add literal expressions in place of the "missing" columns.
The return of the extra src column is one way we can use to distinguish which query a row was returned by. It's not mandatory to return such a column, but it's something I often find useful. (The src column could be removed from each query, if it's not useful for your use case.)
Note that it's also possible to combine the results from more than two queries in this way, we'd just add another UNION ALL and another query.
The column names in the combined resultset are determined from the first query. The column names and aliases in the second query are ignored.
The ORDER BY applies to the entire set, and follows the last select.
Query should be linked via postID
F=feeds table, L=likes table, U1=usertable linked to owned feeds, U2=usertable linked to likes table
SELECT F.postTitle+' posted by '+ U1.username,'liked by'+U2.username
FROM likes L
LEFT JOIN feeds F on (F.postID=L.postID)
LEFT JOIN users U1 on (U1.userID=F.userID)
LEFT JOIN users U2 on (U2.userID=L.userID)
ORDER BY L.date,L.postID DESC
When you write SELECT * FROM feeds,likes... you are implicitly CROSS JOINing both tables. The engine will combine every record in each table with every record in the other. That is far from what you want.
I don't think you should be "linking" both tables, either. What you need, roughly speaking, is to get every post and every like, and then order that big set according to timestamps.
It sounds more like a UNION between two queries, and an ORDER BY applied to the whole UNION. UNIONs are never easy on the eye, by the way...
The thing with UNIONs is that both sub-queries need to return the same amount of columns. Not knowing exactly which columns you have, I'll show you one possible solution:
SELECT activity, timestamp FROM (
( SELECT CONCAT(u.name,' posted ',f.content) as activity, timestamp
FROM user u
JOIN feed f on (f.user_id=u.id)
WHERE f.deleted!=0
) UNION
( SELECT CONCAT(u.name, ' liked a post by ',u2.name) as activity, timestamp
FROM user u
JOIN likes l on (l.user_id=u.id)
JOIN feed f on (l.feed_id=f.id)
JOIN user u2 on (f.user_id=u2.id)
WHERE l.deleted!=0
)
) as whole_result
ORDER by timestamp desc
You should, of course, modify this to match your structure.
Hope this helps!
I think, it's better to use 3rd table, say, "actions", and insert to it real actions. Then just select rows from this table, joined to "posts" & "users" table.
When user posts articles, o likes an article, insert corresponding row to "actions" table.
actions table:
|id|action_name|user_id|post_id| date |
1 posted 3 3 5/7/2014
2 liked 5 3 5/7/2014
3 liked 4 3 6/7/2014
4 posted 5 6 7/7/2014
5 liked 3 6 7/7/2014
SELECT user_name a, post_title b, action_name c FROM actions c LEFT JOIN users a ON a.id=c.user_id LEFT JOIN posts b ON b.id = c.post_id ORDER BY c.date DESC LIMIT 10
Then, in loop, choose how to display this data, according to "action_name".
In such way you can expand your wall for other activities, +use indexes for better database performance.
I have two MySql Tables as follows:
resource
-----------------------------------------------
id name group owner_id
-----------------------------------------------
1 MyResource1 hs 11
2 MyResource2 ms 24
3 MyResource3 ps 11
...
resource_access
-----------------------------------------------
id resource_id user_id
-----------------------------------------------
1 1 12
2 2 24
3 2 11
4 3 15
...
Now, the first table is a list of resources, of course, and their respective owners in the owner_id column. The second table is the result of "sharing" this resource with another user. The table resource_access may contain records with a user_id that is equivalent to the owner_id in a row of the resource_access as a result of messy cleanup from an owner exchange.
I simply want to get the id, name, and group of any resource that a user has access to, whether they are the owner or it has been shared with them. Here is my MySQL query for an example user (24):
SELECT resource.id, resource.name, resource.group
FROM `resource`
INNER JOIN resource_access ON (
resource.owner_id='24'
OR (
resource_access.user_id='24' AND
resource_access.resource_id=resource.id
)
)
Right now, it returns the id, name, and group for resource number 2 multiple times (like twelve). Is there a possible cause for this? I have tried LEFT and RIGHT joins and am getting the same result. There are many records in the resource table, but none with the id of 2. There are no duplicate rows in resource_access sharing the resource with the same user twice.
Thanks in advance.
Use:
SELECT DISTINCT resource.id, resource.name, resource.group
to remove duplicates.
The way an inner join conceptually works is that it produces a full cross-product between the two tables. This cross-product contains a row for each pair of rows in the input tables. Then it keeps the rows that match all the ON and WHERE conditions, and returns this as the result set. If there are multiple matching rows between the two tables, you'll get multiple rows in the result set.
If you were selecting columns from both tables, you would see that they're not actually the same row. They just have the same data from the resource table, but different data from the resource_access table. But you're not showing those latter columns in your result. Using DISTINCT merges all these rows in the result.
Because you are only selecting from the resource table, I would suggest putting the conditions in the where clause rather than using an explicit join:
SELECT r.id, r.name, r.group
FROM `resource` r
WHERE r.owner_id='24' or
EXISTS (select 1
from resource_access ra
where ra.resource_id = r.id and
ra.user_id = '24'
);
With this logic, the "join" cannot product duplicates.
Select the ownership of resources then union it to resources with access.
Resulting user_id column that is different from your WHERE RA.user_id value just means that resource was shared to them instead of them owning the resource. Hope this helps.
SELECT resource.name,resource.group,resource.owner_id AS user_id
FROM resource
WHERE resource.owner_id = '11'
UNION
SELECT R.name,R.group,R.owner_id AS user_id
FROM resource_access RA
LEFT JOIN resource R
ON (R.id=RA.resource_id)
WHERE RA.user_id = '11';
I need to report the number of records that match each of several criteria. For example, how many customers live in each state. I know I can accomplish this through a series of MySQL SELECT statements, but that seems cumbersome and produces a ton of (unnecessary?) MySQL calls.
Can you tell me a better method to use? Can I query the database with one SELECT statement and then use PHP to filter the results to variables?
I'd suggest creating a view for this task just to hide the complexity of the query. Also, in the event that your table schema changes, it is likely that you are still going to want to retrieve this same information from the database. You'd be able to change the view in one place, instead of having to change the queries in, possibly, multiple places to satisfy your schema changes.
I'll just show you the queries, though, since you'd need to know how to do that to create a view anyways.
Sticking with your example of customers living in each state, let's pretend you also want statistics on how many customers share the same last name.
I've setup a mock structure of what your database might be like at this SqlFiddle.
Customers with Same LastName
The following query might be used to get the number of customers with the same last name:
SELECT
LastName AS "Value",
COUNT(*) AS "Count"
FROM Customers
GROUP BY
LastName;
Customers in Same State
Similarly, the customers in the same state might be retrieved with a query as follows:
SELECT
S.Name AS "Value",
COUNT(*) AS "Count"
FROM Customers AS C
INNER JOIN CustomerAddresses AS CA ON C.Id = CA.CustomerId
INNER JOIN Addresses AS A ON CA.AddressId = A.Id
INNER JOIN States AS S ON A.State = S.Id
GROUP BY
A.State;
Getting Your Desired Format
The format that you want is an aggregation of these two queries. You want both returned as a single result set. So, let's workout a schema for the returned table:
ResultType - This will hold a value that corresponds to the type of result. i.e. "State"
Value - This will hold the value of the aggregated column. i.e. "Florida"
Count - This will hold the total number of records that match the aggregated column.
So, now that we have a format, let's create a query that uses our two queries from above, and puts them into this format.
First, I add a new field to each of the above queries: ResultType
For example:
"LastName" AS "ResultType"
Now, I combine my queries into a single query using the UNION ALL statement:
SELECT * FROM (
/* LastName query */
SELECT
"LastName" AS "ResultType",
LastName AS "Value",
COUNT(*) AS "Count"
FROM Customers
GROUP BY
LastName
UNION ALL
/* States query */
SELECT
"State" AS "ResultType",
S.Name AS "Value",
COUNT(*) AS "Count"
FROM Customers AS C
INNER JOIN CustomerAddresses AS CA ON C.Id = CA.CustomerId
INNER JOIN Addresses AS A ON CA.AddressId = A.Id
INNER JOIN States AS S ON A.State = S.Id
GROUP BY
A.State
) AS A
In my SqlFiddle above, this produces an output like:
RESULTTYPE VALUE COUNT
=================================
LastName Jetson 1
LastName Johnson 2
LastName Milton 1
State Florida 2
State Georgia 1
State Utah 1
As you can see, this could get quite complex, so you might consider looking into placing this into a view. Then, you'd be able to query your view, as if it was the table above (ResultType, Value, and Count). That would also allow you to filter on it.
create select query make number of aliens of table and make your related columns aliens which is you want to use.
lest see sample example
SELECT a.id AS id
FROM Table1 AS a
WHERE ...
UNION ALL
SELECT b.name AS name
FROM Table2 AS b
WHERE ...
ORDER BY (a or b) ...
in our project we've got an user table where userdata with name and different kind of scores (overall score, quest score etc. is stored). How the values are calculated doesn't matter, but take them as seperated.
Lets look table 'users' like below
id name score_overall score_trade score_quest
1 one 40000 10000 20000
2 two 20000 15000 0
3 three 30000 1000 50000
4 four 80000 60000 3000
For showing the scores there are then a dummy table and one table for each kind of score where the username is stored together with the point score and a rank. All the tables look the same but have different names.
id name score rank
They are seperated to allow the users to search and filter the tables. Lets say there is one row with the player "playerX" who has rank 60. So if I filter the score for "playerX" I only see this row, but with rank 60. That means the rank are "hard stored" and not only displayed dynamically via a rownumber or something like that.
The different score tables are filled via a cronjob (and under the use of a addional dummy table) which does the following:
copies the userdata to a dummy table
alters the dummy table by order by score
copies the dummy table to the specific score table so the AI primary key (rank) is automatically filled with the right values, representing the rank for each user.
That means: Wheren there are five specific scores there are also five score tables and the dummy table, making a total of 6.
How to optimize?
What I would like to do is to optimize the whole thing and to drop duplicate tables (and to avoid the dummy table if possible) to store all the score data in one table which has the following cols:
userid, overall_score, overall_rank, trade_score, trade_rank, quest_score, quest_rank
My question is now how I could do this the best way and is there another way as the one shown above (with all the different tables)? MYSQL-Statements and/or php-code is welcome.
Some time ago I tried using row numbers but this doesn't work a) because they can't be used in insert statements and b) because when filtering every player (like 'playerX' in the example above) would be on rank 1 as it's the only row returning.
Well, you can try creating a table with the following configuration:
id | name | score_overall | score_trade | score_quest | overall_rank | trade_rank | quest_rank
If you do that, you can use the following query to populate the table:
SET #overall_rank:=-(SELECT COUNT(id) FROM users);
SET #trade_rank:=#overall_rank;
SET #quest_rank:=#overall_rank;
SELECT *
FROM users u
INNER JOIN (SELECT id,
#overall_rank:=#overall_rank+1 AS overall_rank
FROM users
ORDER BY score_overall DESC) ovr
ON u.id = ovr.id
INNER JOIN (SELECT id,
#trade_rank:=#trade_rank+1 AS trade_rank
FROM users
ORDER BY score_trade DESC) tr
ON u.id = tr.id
INNER JOIN (SELECT id,
#quest_rank:=#quest_rank+1 AS quest_rank
FROM users
ORDER BY score_quest DESC) qr
ON u.id = qr.id
ORDER BY u.id ASC
I've prepared an SQL-fiddle for you.
Although I think performance will weigh in if you start getting a lot of records.
A bit of explanation: the #*_rank things are SQL variables. They get increased with 1 on every new row.
I know I can do joins but its not exactly what I want.
I'm making a live chat system that has 2 tables mainly: the main chat table (call it table a), and then a mod table (call this one table b). If a user gets suspended, messages reach over 100 for that channel, or they are over 1 week, the messages get moved from the main chat table to the mod table.
I store the ID of the chat messages as ID(primary) on the main chat table and as chatID on the mod table.
What I'm doing is making a separate page for my Mods and I want to be able to combine the two tables into 1 area but I want them to be ordered by their respective tables.
So lets say we had the following:
Main table ID's: 1,2,4
Mod table ID: 3
I want my results to show up 1,2,3,4 no matter which table the ID is in.
Any help is greatly appreciated!
Edit: I got the answer and this is what I used to do so:
SELECT ab.* FROM
((SELECT ID as table_id FROM a
WHERE roomID = 'newUsers' ORDER BY ID ASC)
UNION ALL
(SELECT chatID as table_id FROM b
WHERE roomID = 'newUsers' ORDER BY chatID ASC)) ab
ORDER BY ab.table_id
Use a UNION in a subselect.
SELECT ab.* FROM (
SELECT 1 as table_id, * FROM a
UNION ALL
SELECT 2 as table_id, * FROM b
) ab
ORDER BY ab.id
If you want the result of table A to appear before table B, change the query to:
SELECT ab.* FROM (
SELECT 1 as table_id, * FROM a
UNION ALL
SELECT 2 as table_id, * FROM b
) ab
ORDER BY ab.table_id, ab.id
Some background
UNION ALL will merge two tables resultsets into one resultset.
UNION will do the same but will eliminate duplicate rows.
This takes time and slows things down, so if you know there will be no duplicate records (or you don't care about dups) use UNION ALL.
See also: http://dev.mysql.com/doc/refman/5.5/en/union.html