I try to merge two tables together and want to get a single table with SQL. My main problem is to overwrite existing values, because in the 2nd table (deltaTable) are some new revision rows, that have the same ID as in the first table (rootTable).
Example:
1) rootTable
ID | REV | NAME
1 | 0 | Part 1
2 | 0 | Part 2
3 | 0 | Part 3
4 | 0 | Part 4
5 | 0 | Part 5
2) deltaTable
ID | REV | NAME
2 | 1 | Part 2
4 | 2 | New Part 4
I want to have the following result:
ID | REV | NAME
1 | 0 | Part 1
2 | 1 | Part 2
3 | 0 | Part 3
4 | 2 | New Part 4
5 | 0 | Part 5
Can anyone help me or give me an hint how to manage the SQL code?
If I understand your question correctly, you could use an UPDATE query:
update
rootTable r inner join deltaTable d
on r.id = d.id
set
r.REV = d.REV,
r.NAME = d.NAME
Please see it working here.
As Hogan suggested, we could add something like where d.rev>r.rev since it should help giving better performances.
An alternative query, if you defined ID as a primary key, is:
insert into rootTable (ID, REV, NAME)
select * from deltaTable
on duplicate key update
REV=values(REV), NAME=values(NAME);
(this will update existing records, and add new ones).
Please see it here.
Related
This question already has answers here:
Selecting boolean in MySQL based on contents of another table
(2 answers)
Closed 4 years ago.
I need some help with a MySQL query which is bringing me a headache.
Basically I have two tables which are related. The first table is called 'books' and it contains the basic information about a book. Then I have an other table called 'user_books' which is related to the previous table and other table (which is irrelevant in the question). This is how the books table looks like:
| b_id | b_name | b_description |
---------------------------------------------------
| 1 | Book1 | Description1 |
| 2 | Book2 | Description2 |
The 'user_books' table has this content:
| ub_userid | ub_bookid | ub_rating | ub_default |
------------------------------------------------------
| 10 | 1 | 5 | 1 |
The user_books table has two primary keys: ub_userid and ub_bookid.
Now I need to make a query which returns all books of the books table and for each book the rating of a given user and a column that in case that there is a record for the book in the user_books table return 1 but if there isn't any book with that bookid return 0.
My desired output given the user 10 would be this:
| b_id | b_name | b_description | ub_default | active |
----------------------------------------------------------
| 1 | Book1 | Description1 | 1 | 1 |
| 2 | Book2 | Description2 | 0 | 0 |
----------------------------------------------------------
I'm using MySQL 5.7
Thanks so much in advance for any kind of help.
select
b.b_id,
b.b_name,
b.b_description,
coalesce(ub.ub_default, 0) as ub_default,
case
when ub.ub_userid is null then 0
else 1
end as active
from books b left outer join
user_books ub
on ub.ub_bookid = b.b_id
where
ub.ub_userid = 10;
This doesn't do any aggregation, so if you have multiple user_books records for one books record, then the books record will be duplicated. But, it shows how to join against a missing row (outer join) and test for whether that outer join row is present or missing.
Here's a SQL Fiddle for MySQL 5.6 http://sqlfiddle.com/#!9/b70ff8/4/0
Background
I have a web application which must remove entries from other tables, filtered through a selection of 'tielists' from table 1 -> item_table 1, table 2, table 3.... now basically my result set is going to be filthy big unless I use a filter statement from another table, using a user_id... so can someone please help me structure my statement as needed? TY!
Tables
cars_belonging_to_user
-----------------------------
ID | user_id | make | model
----------------------------
1 | 1 | Toyota | Camry
2 | 1 |Infinity| Q55
3 | 1 | DMC | DeLorean
4 | 2 | Acura | RSX
Okay, Now the three 'tielists'
name:tielist_one
----------------------------
id | id_of_car | id_x | id_y|
1 | 1 | 12 | 22 |
2 | 2 | 23 | 32 |
-----------------------------
name:tielist_two
-------------------------------
id | id_of_car | id_x | id_z|
1 | 3 | 32 | 22 |
-----------------------------
name: tielist_three
id | id_of_car | id_x | id_a|
1 | 4 | 45 | 2 |
------------------------------
Result Set and Code
echo name_of_tielist_table
// I can structure if statements to echo result sets based upon the name
// Future Methodology: if car_id is in tielist_one, delete id_x from x_table, delete id_y from y_table...
// My output should be a double select base:
--SELECT * tielists from WHERE car_id is 1... output name of tielist... then
--SELECT * from specific_tielist where car_id is 1.....delete x_table, delete y_table...
Considering the list will be massive, and the tielist equally long, I must filter the results where car_id(id) = $variable && user_id = $id....
Side Notes
Only one car id will appear once in any single tielist..
This select statement MUST be filtered with user_id = $variable... (and remember, i'm looking for which car id too)
I MUST HAVE THE NAME of the tielist it comes from able to be echo'd into a variable...
I will only be looking for one single id_of_car at any given time, because this select will be contained in a foreach loop.
I was thinking a union all items would do the trick to select the row, but how can I get the name of the tielist the row is in, and how can the filter be used from the user_id row
If you want performance, I would suggest left outer join instead of union all. This will allow the query to make efficient use of indexes for your purpose.
Based on what you say, a car is in exactly one of the lists. This is important for this method to work. Here is the SQL:
select cu.*,
coalesce(tl1.id_x, tl2.id_x, tl3.id_x) as id_x,
tl1.y, tl2.idz, tl3.id_a,
(case when tl1.id is not null then 'One'
when tl2.id is not null then 'Two'
when tl3.id is not null then 'Three'
end) as TieList
from Cars_Belonging_To_User cu left ouer join
TieList_One tl1
on cu.id_of_car = tl1.id_of_car left outer join
TieList_Two tl2
on cu.id_of_car = tl2.id_of_car left outer join
TieList_Three tl3
on cu.id_of_car = tl3.id_of_car;
You can then add a where clause to filter as you need.
If you have an index on id_of_car for each tielist table, then the performance should be quite good. If the where clause uses an index on the first table, then the joins and where should all be using indexes, and the query will be quite fast.
I have table:
+----+--------+----------+
| id | doc_id | next_req |
+----+--------+----------+
| 1 | 1 | 4 |
| 2 | 1 | 3 |
| 3 | 1 | 0 |
| 4 | 1 | 2 |
+----+--------+----------+
id - auto incerement primary key.
nex_req - represent an order of records. (next_req = id of record)
How can I build a SQL query get records in this order:
+----+--------+----------+
| id | doc_id | next_req |
+----+--------+----------+
| 1 | 1 | 4 |
| 4 | 1 | 2 |
| 2 | 1 | 3 |
| 3 | 1 | 0 |
+----+--------+----------+
Explains:
record1 with id=1 and next_req=4 means: next must be record4 with id=4 and next_req=2
record4 with id=5 and next_req=2 means: next must be record2 with id=2 and next_req=3
record2 with id=2 and next_req=3 means: next must be record3 with id=1 and next_req=0
record3 with id=3 and next_req=0: means that this is a last record
I need to store an order of records in table. It's important fo me.
If you can, change your table format. Rather than naming the next record, mark the records in order so you can use a natural SQL sort:
+----+--------+------+
| id | doc_id | sort |
+----+--------+------+
| 1 | 1 | 1 |
| 4 | 1 | 2 |
| 2 | 1 | 3 |
| 3 | 1 | 4 |
+----+--------+------+
Then you can even cluster-index on doc_id,sort for if you need to for performance issues. And honestly, if you need to re-order rows, it is not any more work than a linked-list like you were working with.
Am able to give you a solution in Oracle,
select id,doc_id,next_req from table2
start with id =
(select id from table2 where rowid=(select min(rowid) from table2))
connect by prior next_req=id
fiddle_demo
I'd suggest to modify your table and add another column OrderNumber, so eventually it would be easy to order by this column.
Though there may be problems with this approach:
1) You have existing table and need to set OrderNumber column values. I guess this part is easy. You can simply set initial zero values and add a CURSOR for example moving through your records and incrementing your order number value.
2) When new row appears in your table, you have to modify your OrderNumber, but here it depends on your particular situation. If you only need to add items to the end of the list then you can set your new value as MAX + 1. In another situation you may try writing TRIGGER on inserting new items and calling similar steps to point 1). This may cause very bad hit on performance, so you have to carefully investigate your architecture and maybe modify this unusual construction.
| postid | ref_postid | title |
| 1 | 0 | Title 1 |
| 2 | 1 | |
| 3 | 1 | |
| 4 | 0 | Title 2 |
| 5 | 4 | |
It´s a table for a discussion forum. When ref_postid = 0, that means it is a main post. When ref_postid is not 0 it is a answer and references to a postid, see table example above. (Only main posts has a title.)
I want to select all rows in the table, but the problem is that I want to display the title for the discussion an answer refers to.
Example: Let´s say I want the row where postid = 2, I also want to get "Title 1" which is the name of the discussion.
I tried doing it with CASE but I just got errors. I´m not very good at this. Is it doable with one query? Or will I have to use two queries?
Thanks for your help!
select ifnull(q.title, a.title) title, ... (other columns)
from posts a
left join posts q on a.ref_postid <> 0 and a.ref_postid = q.postid
I've checked out a few of the stackoverflow questions and there are similar questions, but didn't quite put my fingers on this one.
If you have a table like this:
uid cat_uid itm_uid
1 1 4
2 1 5
3 2 6
4 2 7
5 3 8
6 3 9
where the uid column in auto_incremented and the cat_uid references a
category of relevance to filter on and the itm_uid values are the one
we're seeking
I would like to get a result set that contains the following sample results:
array (
0 => array (1 => array(4,5)),
1 => array (2 => array(6,7)),
2 => array (3 => array(8,9))
)
An example issue is - select 2 records from each category (however many categories there may be) and make sure they are the last 2 entries by uid in those categories.
I'm not sure how to structure the question to allow an answer, and any hints on a method for the solution would be welcome!
EDIT:
This wasn't a very clear question, so let me extend the scenario to something more tangible.
I have a set of records being entered into categories and I would like to select, with as few queries as possible, the latest 2 records entered per category, so that when I list out the contents of those categories, I will have at least 2 records per category (assuming that there are 2 or more already in the database). A similar query was in place that selected the last 100 records and filtered them into categories, but for small numbers of categories with some being updated faster than others can lead to having the top 100 not consisting of members from every category, so to try to resolve that, I was looking for a way to select 2 records from each category (or N-records assuming it's the same per-category) and for those 2 records to be the last entered. A date field is available to sort on, but the itm_uid itself could be used to indicate inserted order.
SELECT cat_uid, itm_uid,
IF( #cat = cat_uid, #cat_row := #cat_row + 1, #cat_row := 0 ) AS cat_row,
#cat := cat_uid
FROM my_table
JOIN (SELECT #cat_row := 0, #cat := 0) AS init
HAVING cat_row < 2
ORDER BY cat_uid, uid DESC
You will have two extra columns in the results, just ignore them.
This is the logic:
We sort the table by cat_uid, uid descending, then we start from the top and give each row a "row number" (cat_row) we reset this row number to zero whenever cat_uid changes:
---------------------------------------
| uid | cat_uid | itm_uid | cat_row |
| 45 | 4 | 34 | 0 |
| 33 | 4 | 54 | 1 |
| 31 | 4 | 12 | 2 |
| 12 | 4 | 51 | 3 |
| 56 | 6 | 11 | 0 |
| 20 | 6 | 64 | 1 |
| 16 | 6 | 76 | 2 |
| ... | ... | ... | ... |
---------------------------------------
now if we keep only the rows that have cat_row < 2 we get the results we want:
---------------------------------------
| uid | cat_uid | itm_uid | cat_row |
| 45 | 4 | 34 | 0 |
| 33 | 4 | 54 | 1 |
| 56 | 6 | 11 | 0 |
| 20 | 6 | 64 | 1 |
| ... | ... | ... | ... |
---------------------------------------
This is called an adjacent tree model or a parent-child tree model. It's one of the simplier tree model where there is only 1 pointer or 1 leaf. You would solve your query with a recursion or using a Self Join. Sadly MySQL doesn't support recursive queries, maybe it's working with prepared statements. I want to suggest you an Self Join. With a Self Join you can get all the rows from the right side and the left side with a special condition.
select t1.cat_uid, t2.cat_uid, t1.itm_uid, t2.itm_uid From t1 Inner Join t2 On t1.cat_uid = t2.cat_uid