I need to create a join query for hierarchical data across 2 tables. These tables can have unlimited amounts of data and their structures are as follows:
group_id group_name group_order
1 group 1 2
2 group 2 1
field_id field_name parent_group field_order
1 field 1 1 1
2 field 2 2 2
3 field 3 2 1
I am currently able to get the correct format of data using 2 select queries with the second query inside a loop created from the results of the first query on the groups table.
The structure of the data I require from the result is as follows:
-group 2
- field 3
- field 2
- group 1
- field 1
Is it possible to get these results from one mysql query? I have read through the mysql document on hierarchical data by I am confused about how to incorporate the join.
Thanks for looking
You shouldn't need to think about it in terms of hierarchical data, you should just be able to select your fields and join on your group information. Try something like:
SELECT *
FROM Fields AS F
INNER JOIN Groups AS G
ON G.group_id = F.parent_group
ORDER BY group_order, field_order
Then you will get each fields as a row with the applicable group, also in the correct group order. Your loop should be able to handle the display you need.
one method
something that may convince you change your db schema
Related
Transport table
id name
1 T1
2 T2
Pallets table
id name
1 P1
2 P2
Transport Pallet Capacity table
id transport_id pallet_id capacity
1 1 1 10
2 1 2 null
3 2 1 20
4 2 2 24
How to generate table like this:
id transport_id pallet_id_1_capacity pallet_id_2_capacity
1 1 10 null
2 2 20 24
Problem: pallets and transports can be added, so, neither quantity is known in advance.
For example, manager adds another pallet type and 'pallet_id_3_capacity' column should be generated (and can show null if no capacity data is yet available).
Another manager can fill 'transport pallet capacity' table later when notified.
Is there a way to build sql in mysql that will care about the above: specifically - dynamic number of pallets?
The SQL select-list must be fixed at the time you write the query. You can't make SQL that auto-expands its columns based on the data it finds.
But your request is common, it's called a pivot-table or a crosstab table.
The only solution is to do this in multiple steps:
Query to discover the distinct pallet ids.
Use application code to build a dynamic SQL query with as many columns as distinct pallet id values found in the first query.
Run the resulting dynamic SQL query.
This is true for all SQL databases, not just MySQL.
See MySQL pivot row into dynamic number of columns for a highly-voted solution for producing a pivot-table query in MySQL.
I am not voting your question as a duplicate of that question, because your query also involves transport_id, which will make the query solution a bit different. But reading about other pivot-table solutions should get you started.
SELECT column_1 FROM table_1,table_2;
When I ran this on my database it returned huge number of rows with duplicate column_1 values. I could not understand why I got these results. Please explain what this query does.
it gives you a cross product from table 1 and table 2
In more layman's terms, it means that for each record in Table A, you get every record from Table B (all possible combinations).
TableA with 3 records and Table B with 3 records gives 9 total records in the result:
TableA-1/B-1
TableA-1/B-2
TableA-1/B-3
TableA-2/B-1
TableA-2/B-2
TableA-2/B-3
TableA-3/B-1
TableA-3/B-2
TableA-3/B-3
Often used as a basis for Cartesian Queries (which themselves are the means to generate, say, a list of future dates based on a recurrence schedule: give me all possible results for the next 6 months, then restrict that set to those whose factor matches my day of the week)
This is 'valid' way of cross joining two tables; it is not the preferred way though. Cross Join would be much clearer. An on condition would then be helpful to limit results,
Imagine that i have 3 friends named Jhon, Ana, Nick; then i have in the other table 2 are T-shirts a red and a yellow and i wanna know witch is from.
So in the query being tableA:Friends and tableB:Tshirts returns:
1|JHON | t-shirt_YELLOW
2|JHON | t-shirt_RED
3|ANA | t-shirt_YELLOW
4|ANA | t-shirt_RED
5|NICK | t-shirt_YELLOW
6|NICK | t-shirt_RED
As you see this join has no relational logic between friends and Tshirts so by evaluating all the posible combination generates what you call duplicates.
I have the following situation. I have a table with all info of article. I will like to compare the same column with it self. because I have multiple type of article. Single product and Master product. the only way that I have to differences it, is by SKU. for example.
ID | SKU
1 | 11111
2 | 11112
3 | 11113
4 | 11113-5
5 | 11113-8
6 | 11114
7 | 11115
8 | 11115-1-W
9 | 11115-2
10 | 11116
I only want to list or / and count only the sku that are full unique. follow th example the sku that are unique and no have variant are (ID = 1, 2, 6 and 10) I will want to create a query where if 11113 are again on the column not cout it. so in total I will be 4 unique sku and not "6 (on total)". Please let me know. if this are possible.
Assuming the length of master SKUs are 5 characters, try this:
select a.*
from mytable a
left join mytable b on b.sku like concat(a.sku, '%')
where length(a.sku) = 5
and b.sku is null
This query joins master SKUs to child ones, but filters out successful joins - leaving only solitary master SKUs.
You can do this by grouping and counting the unique rows.
First, we will need to take your table and add a new column, MasterSKU. This will be the first five characters of the SKU column. Once we have the MasterSKU, we can then GROUP BY it. This will bundle together all of the rows having the same MasterSKU. Once we are grouping we get access to aggregate functions like COUNT(). We will use that function to count the number of rows for each MasterSKU. Then, we will filter out any rows that have a COUNT() over 1. That will leave you with only the unique rows remaining.
Take that unique list and LEFT JOIN it back into your original table to grab the IDs.
SELECT ID, A.MasterSKU
FROM (
SELECT
MasterSKU = SUBSTRING(SKU,1,5),
MasterSKUCount = COUNT(*)
FROM MyTable
GROUP BY SUBSTRING(SKU,1,5)
HAVING COUNT(*) = 1
) AS A
LEFT JOIN (
SELECT
ID,
MasterSKU = SUBSTRING(SKU,1,5)
FROM MyTable
) AS B
ON A.MasterSKU = B.MasterSKU
Now one thing I noticed from you example. The original SKU column really looks like three columns in one. We have multiple values being joined with hypens.
11115-1-W
There may be a reason for it, but most likely this violates first normal form and will make the database hard to query. It's part of the reason why such a complicated query is needed. If the SKU column really represents multiple things then we may want to consider breaking it out into MasterSKU, Version, and Color or whatever each hyphen represents.
how to run query select "sub" grouped by "cat" to return something like this:
SQL query:
select sub
from post
where cat = 1
group by id
to return something like:
3,4,9,14,33,22
table "post"
id cat sub
1 1 3,4,9,14
2 2 1,2
3 2 4,5
4 1 33,22
5 3 1,4
thanks,
It is a very bad idea to store lists of things in character strings. For one thing, your ids are integers, but the strings are characters. More importantly, SQL has a great data structure for storing lists -- it is called a table. You should be using a junction table.
But, sometimes you are stuck with the data you have. In that case, you can use group_concat():
select group_concat(sub)
from post
where cat = 1;
I am asking this question in the hope there is a more efficient (faster) way to pull and insert data in the the tables I am working with.
The basic structure of the data table is
ID Doc_ID Field Value
1 10 Title abc
2 10 Abstract xyz
3 10 Author Bob
4 11 Publisher Bookworms
5 11 Title zzz
6 11 Abstract bbb
7 12 Title aaa
8 12 Sale No
In other words the data tables are row based, each row contain a document id and the corresponding field value. Not all documents have the same number of fields defined. Indeed books may differ radically from magazines.
The data table is 10,000,000 rows typically a document has 100 fields associated with it.
So the performance problem I am finding is pulling a report with reference to 50+ different fields, for example if I have a query list in an order_table the query could be like
select ord.number as 'Order ID', d1.value as 'Title', d2.value as 'Author' .......
from order_table ord
LEFT JOIN data_table as d1 on d1.Doc_ID=ord.Doc_ID and d1.Field='Title'
LEFT JOIN data_table as d2 on d2.Doc_ID=ord.Doc_ID and d2.Field='Author'
........
LEFT JOIN data_table as d50 on d50.Doc_ID=ord.Doc_ID and d50.Field='Qty'
Using LEFT JOINS as there is no guarantee that the field is defined for that document.
Given there may be some WHERE parameters to limit the list to items (in stock for example or below a price) it is a slow query. Indexes don't really much.
Without being able to change the data model, what is the best way to pull volumes of information out?