Following is one of the sample document in couchbase.
{
"name":"abc",
"friends":["a","b","c"],
"bestfriends":["x","y","z"]
}
I want to display "name" based on certain condition on "friends" and "bestfriends".
n1ql Query
select s.name from userdetails s
unnest s.friends as f
unnest s.bestfriends as bf
where f="a" or bf="a"
The above query works fine, if both the array ( friends, bestfriends) are not empty array.
but, even if any one of the array is empty array (ie. "bestfriends":[]), the result is null. How to overcome this?
Use LEFT OUTER UNNEST in both cases.
Related
Below with sub query is not working. When I execute the sub query separately, I can see it returns results. But when this sub query is added to where condition, I get "Results" : []
Select T1.* FROM `masterdata` AS T1
WHERE T1.doc="Calendar"
AND T1.Id=(SELECT SL.DocId FROM `masterdata` AS T
UNNEST T.Sllist AS SL
WHERE T.doc="Cuslist"
AND GtId IN ["1234567"])
Sub query returning the below result
[
sls::76543_77
]
Subquery returns ARRAY of objects, The documents inside subquery are objects. Remove Object use RAW inside subquery (must be projected single element)
You have two options
Option 1: Assume subquery returns single document, if not then query might not give results because your value might be other elements of ARRAY.
Select T1.* FROM `masterdata` AS T1
WHERE T1.doc="Calendar"
AND T1.Id= ((SELECT RAW SL.DocId FROM `masterdata` AS T
UNNEST T.Sllist AS SL
WHERE T.doc="Cuslist"
AND GtId IN ["1234567"])[0])
Option 2: Use IN clause
Select T1.* FROM `masterdata` AS T1
WHERE T1.doc="Calendar"
AND T1.Id IN (SELECT RAW SL.DocId FROM `masterdata` AS T
UNNEST T.Sllist AS SL
WHERE T.doc="Cuslist"
AND GtId IN ["1234567"])
Also checkout Subquery handling and potential query rewrite https://blog.couchbase.com/in-list-handling-improvements-in-couchbase-server-6-5/
I am using NestJS with TypeORM and PostgreSQL. I have a queryBuilder which joins other tables based on the provided array of relations.
const query = this.createQueryBuilder('user');
if (relations.includes('relation1') {
query.leftJoinAndSelect('user.relation1', 'r1');
}
if (relations.includes('relation2') {
query.leftJoinAndSelect('user.relation2', 'r2');
}
if (relations.includes('relation3') {
query.leftJoinAndSelect('user.relation3', 'r3');
}
// 6 more relations
Following that I select a count on another table.
query
.leftJoin('user.relation4', 'r4')
.addSelect('COUNT(case when r4.value > 10 then r4.id end', 'user_moreThan')
.addSelect('COUNT(case when r4.value < 10 then r4.id end', 'user_lessThan')
.groupBy('user.id, r1.id, r2.id, r3.id ...')
And lastly I use one of the counts (depending on the request) for ordering the result with orderBy.
Now, of course, based on the relations parameter, the requirements for the groupBy query change. If I join all tables, TypeORM expects all of them to be present in groupBy.
I initially had the count query separated, but that was before I wanted to use the result for ordering.
Right now I planned to just dynamically create the groupBy string, but this approach somehow feels wrong and I am wondering if it is in fact the way to go or if there is a better approach to achieving what I want.
You can add group by clause conditionally -
if (relations.includes('relation1') {
query.addGroupBy('r1.id');
}
I need to write a n1ql query which demands another sub-query in select clause. As it is mandatory to use 'USE KEYS' while writing subqueries in n1ql. How to write USE KEYS clause for an inner joined query, below is an example of same case:
select meta(m).id as _ID, meta(m).cas as _CAS,
(select c.description
from bucketName p join bucketName c on p.categoryId = c.categoryId and p.type='product' and
c.type='category' and p.masterId=m.masterId ) as description //--How to use USE KEYS here ?
from bucketName m where m.type='master' and m.caseId='12345'
My requirment is to fetch some value from another 2 joined tables. however, I simplified above query to make it more understandable.
Please suggest the correct way to implement.
Also, is writting
sub-queries in n1ql is better than fetching documents seperatly and
merging them in coding?
Non FROM CLAUSE, correlated sub queries requires USE KEYS due to global secondary indexes queries can take long time and resources. This is restriction at present in the N1QL. If you can derive p's document key from the m you can give that as USE KEYS in p.
Otherwise you have two options
Option 1: As your subquery is in the projection Use ANSI JOIN https://blog.couchbase.com/ansi-join-support-n1ql/
SELECT META(m).id AS _ID, META(m).cas AS _CAS, c.description
FROM bucketName AS m
LEFT JOIN bucketName AS p ON p.masterId=m.masterId AND p.type='product'
LEFT JOIN bucketName AS c ON c.type='category' AND p.categoryId = c.categoryId
WHERE m.type='master' AND m.caseId='12345';
CREATE INDEX ix1 ON (caseId) WHERE type='master';
CREATE INDEX ix2 ON (masterId, categoryId) WHERE type='product';
CREATE INDEX ix3 ON (categoryId, description) WHERE type='category';
NOTE: If there is no Unique relation m to p to c JOIN can produce more results.
If that is case, you can do GROUP BY META(m).id, META(m).cas and
ARRAY_AGG(c.description). All descriptions are given as ARRAY.
Option 2:
As described by you issue two separate quires and merge in the application.
right now I am "learning" Postgres SQL. I have 3 tables:
1) User: userId
2) Stack :stackId
3) User_Stack: userId, stackId
Now I want to fetch all stacks belonging to one user, given the userId. I understand I need to use Joins, but thats were I get stuck... I try it like this:
SELECT * FROM "Stack" LEFT OUTER JOIN "User_Stack" ON ('User_Stack.stackId' = 'Stack.stackId') WHERE "userId" = '590855';
Error: The returned data is empty.
PS: Is there any GUI Query builder out there ? Or do you have any other tips how to systematically create queries ?
EDIT: If I change the query to this:
SELECT * FROM "Stack" INNER JOIN "User_Stack" ON (User_Stack.stackId = Stack.stackId) WHERE "userId" = '590855';
I get the following error:
Kernel error: ERROR: missing FROM-clause entry for table "user_stack"
LINE 1: SELECT * FROM "Stack" INNER JOIN "User_Stack" ON (User_Stack...
Your main error is in the join. If you do 'something' = 'other' you're comparing string literals, not getting anything from the database. So this will always return false. You will want to compare table1.field1 = table2.field2
Another thing is the LEFT OUTER JOIN. I'm pretty sure you want an INNER JOIN since you want only fields that exist in the other table.
Also don't use double quotes for fields and table names since then the database will require case sensitivity and usually it's not good to have case sensitive names. You can use them with lowercase names if you need and always create them in lowercase.
Numbers also don't need to be quoted, it will just cause more processing when the system has to convert them from text to numbers.
I searched a lot about sorting elements by sum of votes (in another model), like I do in SQL here :
SELECT item.* FROM item
LEFT JOIN (
SELECT
vote.item,
SUM(vote.value) AS vote.rating
FROM vote
GROUP BY vote.item
) AS res ON item.id = vote.item
ORDER BY res.rating DESC
Is there a way to do it via waterline methods ?
I think you can't do the left join with simple waterline methods, but you can use the .query method to execute your raw SQL syntax.
Sails MySQL adapter makes sum('field') conflict with sort('field'). It will generate SQL query like:
SELECT SUM(table.field) AS field FROM table ORDER BY table.field;
But I want:
SELECT SUM(table.field) AS field FROM table ORDER BY field;
It same as:
SELECT SUM(table.field) AS f FROM table ORDER BY f;
My solution is using lodash.sortBy() to process results. https://lodash.com/docs/4.16.4#sortBy