I wonder which has better performance in this case. First of all, I want to show to the user his medical information. I have two tables
user
-----
id_user | type_blood | number | ...
1 O 123
2 A+ 442
user_allergies
-----------
id_user | name
1 name1
1 name2
I want to return:
JSON {id_user=1, type_blood=0, allergies=(name1,name2)}
So, Its better do a JOIN for user and user_allergies and iterate, or maybe two SELECT?
But if then I have another table like user_allergies, that the result can be:
user_another_table
-----------
id_user | name
1 namet1
1 namet2
1 namet3
JSON {id_user=1, type_blood=0, allergies=(name1,name2), table=(namet1,namet2,namet3)}
It's better three SELECT or a JOIN, but then I have to iterate on the results and I can't imagine a esay way. A JOIN can give me a result like:
id_user | type_blood | allergy_name | another_table_name
1 O name1 namet1
1 O name1 namet2
1 O name1 namet3
1 O name2 namet1
1 O name2 namet2
1 O name2 namet3
Is there any way to extract:
id_user | type_blood | allergy_name | another_table_name
1 O name1 namet1
1 O name2 namet2
1 O namet3
Thanks community, I'm newbie in SQL
Depending on the data - there is no way to get the 2nd set of results you've shown, if the 1st set of results shows the values. The 2nd one is throwing data away - in this case allergy 'name2' for another_table_name 'namet3'. This is why you get many rows back with repeated data.
You can use the group by clause to restrict this in some cases, but again - it won't let you throw away data like that.
You could try using the COALESCE clause, if your DB supports it.
If not, I think you're going to have to construct your JSON in some business logic, in which case its fine to read the data in a 3-way join. You order by the user id and either create or append the row data to the JSON document depending if a user record is present or not (if you order by user id, you only need to keep track of when the user id value changes).
Alternatively, you can read a list of users and single-item data in one query, and then ht the DB again for the repeating data.
Related
Say I have the following data:
Passes
ID | Pass_code
-----------------
100 | 2xBronze
101 | 1xGold
102 | 1xSilver
103 | 2xSteel
Passengers
ID | Passengers
-----------------
100 | 2
101 | 5
102 | 1
103 | 3
I want to count then create a ticket in the output of:
ID 100 | 2 pass (bronze)
ID 101 | 5 pass (because it is gold, we count all passengers)
ID 102 | 1 pass (silver)
ID 103 | 2 pass (steel)
I was thinking something like the code below however, I am unsure how to finish my case statement. I want to substring pass_code so that we get show pass numbers e.g '2xBronze' should give me 2. Then for ID 103, we have 2 passes and 3 customers so we should output 2.
Also, is there a way to firstly find '2xbronze' if the pass_code contained lots of other things such as '101001, 1xbronze, FirstClass' - this may change so i don't want to substring, could we search for '2xbronze' and then pull out the 2??
SELECT
CASE
WHEN Passes.pass_code like '%gold%' THEN Passengers.passengers
WHEN Passes.pass_code like '%steel%' THEN SUBSTRING(passes.pass_code, 1,1)
WHEN Passes.pass_code like '%bronze%' THEN SUBSTRING(passes.pass_code, 1,1)
WHEN Passes.pass_code like '%silver%' THEN SUBSTRING(passes.pass_code, 1,1)
else 0 end as no,
Passes.ID,
Passes.Pass_code,
Passengers.Passengers
FROM Passes
JOIN Passengers ON Passes.ID = Passengers.ID
https://dbfiddle.uk/?rdbms=oracle_18&fiddle=db698e8562546ae7658270e0ec26ca54
So assuming you are indeed using Oracle (as your DB fiddle implies).
You can do some string magic with finding position of a splitter character (in your case the x), then substringing based on that. Obviously this has it's problems, and x is a bad character seperator as well.. but based on your current set.
WITH PASSCODESPLIT AS
(
SELECT PASSES.ID,
TO_Number(SUBSTR(PASSES.PASS_CODE, 0, (INSTR(PASSES.PASS_CODE, 'x')) - 1)) AS NrOfPasses,
SUBSTR(PASSES.PASS_CODE, (INSTR(PASSES.PASS_CODE, 'x')) + 1) AS PassType
FROM Passes
)
SELECT
PASSCODESPLIT.ID,
CASE
WHEN PASSCODESPLIT.PassType = 'gold' THEN Passengers.Passengers
ELSE PASSCODESPLIT.NrOfPasses
END AS NrOfPasses,
PASSCODESPLIT.PassType,
Passengers.Passengers
FROM PASSCODESPLIT
INNER JOIN Passengers ON PASSCODESPLIT.ID = Passengers.ID
ORDER BY PASSCODESPLIT.ID ASC
Gives the result of:
ID NROFPASSES PASSTYPE PASSENGERS
100 2 bronze 2
101 5 gold 5
102 1 silver 1
103 2 steel 3
As can also be seen in this fiddle
But I would strongly advise you to fix your table design. Having multiple attributes in the same column leads to troubles like these. And the more variables/variations you start storing, the more 'magic' you need to keep doing.
In this particular example i see no reason why you don't simply have the 3 columns in Passes, also giving you the opportunity to add new columns going forward. I.e. to keep track of First class.
You can extract the numbers using regexp_substr(). So I think this does what you want:
SELECT (CASE WHEN p.pass_code LIKE '%gold%'
THEN TO_NUMBER(REGEXP_SUBSTR(p.pass_code, '^[0-9]+'))
ELSE pp.passengers
END) as num,
p.ID, p.Pass_code, pp.Passengers
FROM Passes p JOIN
Passengers pp
ON p.ID = pp.ID;
Here is a db<>fiddle.
This converts the leading digits in the code to a number. Also note the use of table aliases to simplify the query.
I have the following SQL query:
SELECT TOP 3 accounts.username
,COUNT(accounts.username) AS count
FROM relationships
JOIN accounts ON relationships.account = accounts.id
WHERE relationships.following = 4
AND relationships.account IN (
SELECT relationships.following
FROM relationships
WHERE relationships.account = 8
);
I want to return the total count of accounts.username and the first 3 accounts.username (in no particular order). Unfortunately accounts.username and COUNT(accounts.username) cannot coexist. The query works fine removing one of the them. I don't want to send the request twice with different select bodies. The count column could span to 1000+ so I would prefer to calculate it in SQL rather in code.
The current query returns the error Column 'accounts.username' is invalid in the select list because it is not contained in either an aggregate function or the GROUP BY clause. which has not led me anywhere and this is different to other questions as I do not want to use the 'group by' clause. Is there a way to do this with FOR JSON AUTO?
The desired output could be:
+-------+----------+
| count | username |
+-------+----------+
| 1551 | simon1 |
| 1551 | simon2 |
| 1551 | simon3 |
+-------+----------+
or
+----------------------------------------------------------------+
| JSON_F52E2B61-18A1-11d1-B105-00805F49916B |
+----------------------------------------------------------------+
| [{"count": 1551, "usernames": ["simon1", "simon2", "simon3"]}] |
+----------------------------------------------------------------+
If you want to display the total count of rows that satisfy the filter conditions (and where username is not null) in an additional column in your resultset, then you could use window functions:
SELECT TOP 3
a.username,
COUNT(a.username) OVER() AS cnt
FROM relationships r
JOIN accounts a ON r.account = a.id
WHERE
r.following = 4
AND EXISTS (
SELECT 1 FROM relationships t1 WHERE r1.account = 8 AND r1.following = r.account
)
;
Side notes:
if username is not nullable, use COUNT(*) rather than COUNT(a.username): this is more efficient since it does not require the database to check every value for nullity
table aliases make the query easier to write, read and maintain
I usually prefer EXISTS over IN (but here this is mostly a matter of taste, as both techniques should work fine for your use case)
I have two tables.
Order
Replication.
A single order record can have multiple Replication records. I want to join these two tables, such that i always retrieve a single record out of the join even if multiple records exist.
Sample data
Replication table:
ORDID | STATUS | ID | ERRORMSG | HTTPSTATUS | DELIVERYCNT
=========================================================
1717410307 1 JBM-9e92ae0c NULL 200 1
----------
1717410307 1 JBM-9fb59af1 NULL 400 -99
----------
1717410308 1 JBM-0764b091 NULL 403 1
----------
1717410308 1 JBM-0764b091 NULL 200 1
Order Table:
ORDID | ORDTYPE | DATE
----------
1717410307 CAR 22-SEP-2011
1717410308 BUS 23-SEP-2011
How can i make a join effectively so as , i will get as many records in order table and a replication table that should be dynamically selected on a priority basis.
The priority can be defined as :
Any record with a delivery count of -99
HTTPSTATUS != 200
Please guide me how can i proceed with this joining?
Please let me know if you need any clarification.
Your help is much appreciated!
Is it possible to use ORDER BY clause based on the HTTPSTATUS and DELIVERYCNT?
In that case you can write a specific ORDER BY and getting the TOP 1 from it (don't know which RDBMS do you use) or getting ROW_NUMBER() OVER (ORDER BY ... ) AS RowN WHERE RowN = 1
But this is the ugly (yet quick) solution.
The other option is to make a subquery where you add a new column which will make the priority calculation.
To make the query effective you should consider indexing (or using RDBMS specific solutions like included columns)
I have a query I need to perform to show search results for a project. What needs to happen, I need to sort the results by the "horsesActiveDate" and this applies to all of them except for any ad with the adtypesID=7. Those results are sorted by date but they must always result after all other ads.
So I will have all my ads in the result set be ordered by the Active Date AND adtypesID != 7. After that, I need all adtypesID=7 to be sorted by Active Date and appended at the bottom of all the results.
I'm hoping to put this in one query instead of two and appending them together in PHP. The way the code is written, I have to find a way to get it all in one query.
So here is my original query which has worked great until I had to ad the adtypesID=7 which has different sorting requirements.
This is the query that exists now that doesn't take into account the adtypesID for sorting.
SELECT
horses.horsesID,
horsesDescription,
horsesActiveDate,
adtypesID,
states.statesName,
horses_images.himagesPath
FROM horses
LEFT JOIN states ON horses.statesID = states.statesID
LEFT JOIN horses_images ON horses_images.himagesDefault = 1 AND horses_images.horsesID = horses.horsesID AND horses_images.himagesPath != ''
WHERE
horses.horsesStud = 0
AND horses.horsesSold = 0
AND horses.horsesID IN
(
SELECT DISTINCT horses.horsesID
FROM horses
LEFT JOIN horses_featured ON horses_featured.horsesID = horses.horsesID
WHERE horses.horsesActive = 1
)
ORDER BY adtypesID, horses.horsesActiveDate DESC
My first thought was to do two queries where one looked for all the ads that did not contain adtypesID=7 and sort those as the query does, then run a second query to find only those ads with adtypesID=7 and sort those by date. Then take those two results and append them to each other. Since I need to get this all into one query, I can't use a php function to do that.
Is there a way to merge the two query results one after the other in mysql? Is there a better way to run this query that will accomplish this sorting?
The Ideal Results would be as below (I modified the column names so they would be shorter):
ID | Description | ActiveDate | adtypesID | statesName | himagesPath
___________________________________________________________________________
3 | Ad Text | 06-01-2010 | 3 | OK | image.jpg
2 | Ad Text | 05-31-2010 | 2 | LA | image1.jpg
9 | Ad Text | 03-01-2010 | 4 | OK | image3.jpg
6 | Ad Text | 06-01-2010 | 7 | OK | image5.jpg
6 | Ad Text | 05-01-2010 | 7 | OK | image5.jpg
6 | Ad Text | 04-01-2010 | 7 | OK | image5.jpg
Any help that can be provided will be greatly appreciated!
I am not sure about the exact syntax in MySQL, but something like
ORDER BY case when adtypesID = 7 then 2 else 1 end ASC, horses.horsesActiveDate DESC
would work in many other SQL dielects.
Note that most SQL dialects allow the order by to not only be a column, but an expression.
This should work:
ORDER BY (adtypesID = 7) ASC, horses.horsesActiveDate DESC
Use a Union to append two queries together, like this:
SELECT whatever FROM wherever ORDER BY something AND adtypesID!=7
UNION
SELECT another FROM somewhere ORDER BY whocares AND adtypesID=7
http://dev.mysql.com/doc/refman/5.0/en/union.html
I re-wrote your query as:
SELECT h.horsesID,
h.horsesDescription,
h.horsesActiveDate,
adtypesID,
s.statesName,
hi.himagesPath
FROM HORSES h
LEFT JOIN STATES s ON s.stateid = h.statesID
LEFT JOIN HORSES_IMAGES hi ON hi.horsesID = h.horsesID
AND hi.himagesDefault = 1
AND hi.himagesPath != ''
LEFT JOIN HORSES_FEATURED hf ON hf.horsesID = h.horsesID
WHERE h.horsesStud = 0
AND h.horsesSold = 0
AND h.horsesActive = 1
ORDER BY (adtypesID = 7) ASC, h.horsesActiveDate DESC
The IN subquery, using a LEFT JOIN and such, will mean that any horse record whose horsesActive value is 1 will be returned - regardless if they have an associated HORSES_FEATURED record. I leave it to you for checking your data to decide if it should really be an INNER JOIN. Likewise for the STATES table relationship...
Hypothetical situation: I work for a custom sign-making company, and some of our clients have submitted more sign designs than they're currently using. I want to know what signs have never been used.
3 tables involved:
table A - signs for a company
sign_pk(unique) | company_pk | sign_description
1 --------------------1 ---------------- small
2 --------------------1 ---------------- large
3 --------------------2 ---------------- medium
4 --------------------2 ---------------- jumbo
5 --------------------3 ---------------- banner
table B - company locations
company_pk | company_location(unique)
1 ------|------ 987
1 ------|------ 876
2 ------|------ 456
2 ------|------ 123
table C - signs at locations (it's a bit of a stretch, but each row can have 2 signs, and it's a one to many relationship from company location to signs at locations)
company_location | front_sign | back_sign
987 ------------ 1 ------------ 2
987 ------------ 2 ------------ 1
876 ------------ 2 ------------ 1
456 ------------ 3 ------------ 4
123 ------------ 4 ------------ 3
So, a.company_pk = b.company_pk and b.company_location = c.company_location. What I want to try and find is how to query and get back that sign_pk 5 isn't at any location. Querying each sign_pk against all of the front_sign and back_sign values is a little impractical, since all the tables have millions of rows. Table a is indexed on sign_pk and company_pk, table b on both fields, and table c only on company locations. The way I'm trying to write it is along the lines of "each sign belongs to a company, so find the signs that are not the front or back sign at any of the locations that belong to the company tied to that sign."
My original plan was:
Select a.sign_pk
from a, b, c
where a.company_pk = b.company_pk
and b.company_location = c.company_location
and a.sign_pk *= c.front_sign
group by a.sign_pk having count(c.front_sign) = 0
just to do the front sign, and then repeat for the back, but that won't run because c is an inner member of an outer join, and also in an inner join.
This whole thing is fairly convoluted, but if anyone can make sense of it, I'll be your best friend.
How about something like this:
SELECT DISTINCT sign_pk
FROM table_a
WHERE sign_pk NOT IN
(
SELECT DISTINCT front_sign sign
FROM table_c
UNION
SELECT DISTINCT rear_sign sign
FROM table_c
)
ANSI outer join is your friend here. *= has dodgy semantics and should be avoided
select distinct a.sign_pk, a.company_pk
from a join b on a.company_pk = b.company_pk
left outer join c on b.company_location = c.company_location
and (a.sign_pk = c.front_sign or a.sign_pk = c.back_sign)
where c.company_location is null
Note that the where clause is a filter on the rows returned by the join, so it says "do the joins, but give me only the rows that didn't to join to c"
Outer join is almost always faster than NOT EXISTS and NOT IN
I would be tempted to create a Temp table for the inner join and then outer join that.
But it really depends on the size of your data sets.
Yes, the schema design is flawed, but we can't always fix that!