I have a table called "MYTABLE" that looks like this:
ID | TIMESTAMP | DATA
1 | 150233939 | xxx
2 | 150233940 | xxx
3 | 150233941 | xxx
4 | 150233942 | xxx
5 | 150233943 | xxx
6 | 150233944 | xxx
7 | 150233945 | xxx
8 | 150233946 | xxx
9 | 150233947 | xxx
I can easily get all of the items using:
SELECT * FROM MYTABLE
But this table is going to get massive and it contains data points that will be shown on a graph. So instead of getting ALL of the data points, I want them spaced out. For example, I want a query that would return
1,3,5,7,9
Or:
1,4,8,9
Is there a way to do this on the query level?
UPDATE
I was able to get the data like so:
SELECT * FROM MYTABLE where mod(id,5) = 0
This divides the data quite nicely, but it is SUPER SLOW. Is there another way to make it faster?
Related
I'm working on a database with a category tree that's hierarchical. I'd like to be able to be able to write a query that returns all of the parents. For example, assume this structure/content. A parent of 0 means that it's a root element, no parents.
ID | Name | Parent
1 | Tools | 0
2 | Drill | 1
3 | Impact | 2
4 | Cordless | 2
5 | Series X | 4
How could I write a query that would get all of the parents of Series x (ID 5)? I don't care if it's inclusive of ID 5, since I would already have that one. I'd like to see it return the below results.
ID | Name | Parent
1 | Tools | 0
2 | Drill | 1
4 | Cordless | 2
5 | Series X | 4
Bonus if there's a way to find how many generations they are at the same time. Something like:
ID | Name | Parent | Generation
1 | Tools | 0 | 0
2 | Drill | 1 | 1
4 | Cordless | 2 | 2
5 | Series X | 4 | 3
I'm really stuck on this right now. I am thinking it might need to be a custom sql function?
In MySQL 8.0, they now support recursive CTE queries:
WITH RECURSIVE cte AS (
SELECT * FROM MyTable WHERE id = 5
UNION ALL
SELECT MyTable.* FROM cte JOIN MyTable WHERE MyTable.id = cte.parent
)
SELECT * FROM cte ORDER BY id;
Getting the "Generation" when your CTE starts at the leaf of the hierarchy is tricky.
If you are using a version of MySQL older than 8.0, you may like my answer to What is the most efficient/elegant way to parse a flat table into a tree? or my presentation Recursive Query Throwdown.
Here is my table:
| ID | NUMBER |
| 1 | 523 |
| 2 | 293 |
| 3 | 948 |
And now, I want to get all NUMBER values but I want to add in result two numbers - 48 - (without upadting existing results). So finally I want print these results:
| NUMBER |
| 48523 |
| 48293 |
| 48948 |
So I need a query, something like this:
SELECT '48' + `number` FROM `table`
but this query doesn't work fine (this query only update column name from NUMBER to 48 + NUMBER).
Any ideas?
Thanks.
You need CONCAT
SELECT CONCAT('48' , `number`) AS number FROM table
Demo
In Mysql, I have the following table:
id | paramname | paramcategory | value |
---+-------------+-------------------+-----------------+
1 | width | dimensions | 240 |
2 | height | dimensions | 400 |
3 | param1 | category1 | some value 1 |
4 | param2 | category1 | some value 2 |
5 | param3 | category10 | some value 100 |
...
I'd like to have a query that will return a table with only several rows concatenated, and all other rows should remain intact, something like this:
paramname | value |
--------------+--------------+
width, height | 240 x 400 |
param1 | some value 1 |
...
I'm thinking about concatenating based on the needed paramcategory, but if possible/needed, concatenation can happen for specific paramnames as well. Whatever is easier/simpler.
Any help please?
Looking at this problem from above, you are going to have to 'UNION' 2 queries together. The first part of the union is your concat'd results, the second your original rows. For the first part you are going to need to do a self join on this table, along the lines of
select concat(a.paramname, b.paramname), concat(a.value, b.value) from table a, table b where a.paramcategory = b.paramcategory
along those lines....
Actually if you swap the 2 parts of the union around, you'll keep the original column names too.
In my table I have two columns "sku" and "fitment". The sku represents a part and the fitment represents all the vehicles this part will fit on. The problem is, in the fitment cells, there could be up to 20 vehicles in there, separated by ^^. For example
**sku -- fitment**
part1 -- Vehichle 1 information ^^ vehichle 2 information ^^ vehichle 3 etc
I am looking to split the cells in the fitment column, so it would look like this:
**sku -- fitment**
part1 -- Vehicle 1 information
part1 -- Vehicle 2 information
part1 -- Vehicle 3 information
Is this possible to do? And if so, would a mySQL db be able to handle hundreds of thousands of items "splitting" like this? I imagine it would turn my db of around 250k lines to about 20million lines. Any help is appreciated!
Also a little more background, this is going to be used for a drill down search function so I would be able to match up parts to vehicles (year, make, model, etc) so if you have a better solution, I am all ears.
Thanks
Possible duplicate of this: Split value from one field to two
Unfortunately, MySQL does not feature a split string function. As in the link above indicates there are User-defined Split function's.
A more verbose version to fetch the data can be the following:
SELECT SUBSTRING_INDEX(SUBSTRING_INDEX(fitment, '^^', 1), '^^', -1) as fitmentvehicle1,
SUBSTRING_INDEX(SUBSTRING_INDEX(fitment, '^^', 2), '^^', -1) as fitmentvehicle2
....
SUBSTRING_INDEX(SUBSTRING_INDEX(fitment, '^^', n), '^^', -1) as fitmentvehiclen
FROM table_name;
Since your requirement asks for a normalized format (i.e. not separated by ^^) to be retrieved, it is always better to store it in that way in the first place. And w.r.t the DB size bloat up, you might want to look into possibilities of archiving older data and deleting the same from the table.
Also, you should partition your table using an efficient partitioning strategy based on your requirement. It would be more easier to archive and truncate a partition of the table itself, instead of row by row.
E.g.
DROP TABLE IF EXISTS my_table;
CREATE TABLE my_table (user_id INT NOT NULL PRIMARY KEY,stuff VARCHAR(50) NOT NULL);
INSERT INTO my_table VALUES (101,'1,2,3'),(102,'3,4'),(103,'4,5,6');
SELECT *
FROM my_table;
+---------+-------+
| user_id | stuff |
+---------+-------+
| 101 | 1,2,3 |
| 102 | 3,4 |
| 103 | 4,5,6 |
+---------+-------+
SELECT * FROM ints;
+---+
| i |
+---+
| 0 |
| 1 |
| 2 |
| 3 |
| 4 |
| 5 |
| 6 |
| 7 |
| 8 |
| 9 |
+---+
SELECT DISTINCT user_id
, SUBSTRING_INDEX(SUBSTRING_INDEX(stuff,',',i2.i*10+i1.i+1),',',-1) x
FROM my_table
, ints i1
, ints i2
ORDER
BY user_id,x;
+---------+---+
| user_id | x |
+---------+---+
| 101 | 1 |
| 101 | 2 |
| 101 | 3 |
| 102 | 3 |
| 102 | 4 |
| 103 | 4 |
| 103 | 5 |
| 103 | 6 |
+---------+---+
I am trying to do multiple joins on the same MySQL table, but am not getting the results that I expect to get. Hopefully someone can point out my mistake(s).
Table 1 - cpe Table
|id | name
|----------
| 1 | cat
| 2 | dog
| 3 | mouse
| 4 | snake
-----------
Table 2 - AutoSelect
|id | name | cpe1_id | cpe2_id | cpe3_id |
|-----------------------------------------------
| 1 | user1 | 1 | 3 | 4 |
| 2 | user2 | 3 | 1 | 2 |
| 3 | user3 | 3 | 3 | 2 |
| 4 | user4 | 4 | 2 | 1 |
------------------------------------------------
I would like to see an output of
user1 | cat | mouse | snake |
user2 | mouse | snake | dog |
..etc
Here is what I have tried
SELECT * FROM AutoSelect
LEFT JOIN cpe ON
( cpe.id = AutoSelect.cpe1_id ) AND
( cpe.id = AutoSelect.cpe2_id ) AND
( cpe.id = AutoSelect.cpe3_id )
I get blank results. I thought i knew how to do these joins, but apparently when I'm trying to match cpe?_id with the name of the cpe table.
Thanks in advance for any assistance.
You need left join 3 times as well. Currently your query only joins 1 time with 3 critieria as to the join. This should do:
SELECT a.name, cpe1.name, cpe2.name, cpe3.name FROM AutoSelect as a
LEFT JOIN cpe as cpe1 ON ( cpe1.id = a.cpe1_id )
LEFT JOIN cpe as cpe2 ON ( cpe2.id = a.cpe2_id )
LEFT JOIN cpe as cpe3 ON ( cpe3.id = a.cpe3_id )
And you probably mean to INNER JOIN rather than LEFT JOIN unless NULL values are allowed in your AutoSelect table.
I think your design is wrong.
With tables like that, you get it the way it's meant to be in relational databases :
table 1 : animal
id name
1 cat
2 dog
3 mouse
4 snake
table 2 : user
|id | name |
|--------------
| 1 | user1 |
| 2 | user2 |
| 3 | user3 |
| 4 | user4 |
table 3 : association
|id_user | id_animal|
|--------------------
| 1 | 1 |
| 1 | 3 |
| 1 | 4 |
| 2 | 3 |
| 2 | 1 |
| 2 | 2 |
| 3 | 3 |
| 3 | 2
| 4 | 4 |
| 4 | 2 |
| 4 | 1 |
---------------------
Then :
select u.name, a.name from user u, animal a, association ass where ass.user_id = u.id and ass.animal_id = a.id;
In this case, your solution won't produce a good dynamic database. There are other ways to make combinations of multiple tables. I can show you by my own database what you should use and when you should use this solution. The scheme is in dutch, but you'll probably understand the keywords.
Like you, I had to combine my windmills with a kWh-meter, which has to measure the energyproduction of my windmills. What you should do, is this case, is making another table(in my case molenkWhlink). Make sure your tables are INNODB-types(for making Foreign keys). What I've done is combining my meters and mills by putting a pointer(a foreign key) of their ID(in Dutch Volgnummer) in the new table. An advantage you may not need, but I certainly did, is the fact I was able to extend the extra table with connection and disconnection info like Timestamps and metervalues when linking or unlinking. This makes your database way more dynamic.
In my case, I Also had a table for meassurements(metingoverzicht). As you can see in the scheme, I've got 2 lines going from Metingoverzicht to molenkwhlink. The reason for this is quite simple. All meassurements I take, will be saved in table Metingoverzicht. Daily meassurements(which are scheduled) will have a special boolean put on, but unscheduled meassurements, will also me saved here, with the bollean turned off. When switching meters, I need the endvalue from the leaving meter and the startvalue from the new meter, to calculate the value of todays eneryproduction. This is where your solution comes in and an extra table won't work. Usually, when you need just one value from another table a JOIN will be used. The problem in this case is, I've got 2 meassurementIDs in 1 link(1 for connecting and 1 for disconnecting). They both point to the same tablecolumn, because they both need to hold the same type of information. That is when you can use a double JOIN from one table towards the other. Because, both values will only be used once, and just needed to be saved in a different place to avoid having 1 action stored on different locations, which should always be avoided.
http://s1101.photobucket.com/user/Manuel_Barcelona/media/schemedatabase.jpg.html