I was using mysql earlier. Now for specific reason had to move to cassandra. Now I am facing some incompatibility issue with my mysql queries in cassandra cql . For example when case in mysql it seems does not support in cql . How to make this sql work in cassandra
SELECT age, sum(case when age>0 and age<=10 then 1 else 0 end) as x0,
sum(case when age>10 and age<=20 then 1 else 0 end) as x1
FROM user_table where location_id=24
I am getting the following error:
SyntaxException: line 1:32 no viable alternative at input 'when' (... age, sum([case] when...)
Thanks in advance.
It's not possible at all to map this query to cql. Things are different with cassandra.
When designing your system you should have in mind, what queries you have to run and design it accordingly. This is given by the fact that you can only access the data in a way like it was written.
Last but not least the part where you are creating sums, is probably something which you would like to do on the client side.
Best
Related
I have my new Spring Boot project with SQL Server and I need to replace my MySQL native query on the Repository method in my old project with SQL Server native query. It's a complex query with the case when expression in where condition. When I try testing that query in SQL Server Management Studio it shows errors like the image below.
enter image description here
And here's my old native query use with MySQL on the Repository method I want to replace it with SQL Server
enter image description here
Please help me to find the solution.
Thank you in advance!!
This is what you have and what you should have posted as text within your question. As text it becomes searchable and copyable by people trying to help YOU.
case when #num = 1 then p.merchant_name = #query else 1=1 end
CASE is an expression in TSQL. It is not a control-of-flow construct like it is in many other languages. To use an "optional" filter, you need to construct a boolean expression using CASE which handles the "optional" attribute correctly. Often this is done with a bit more complexity using CASE like this:
case when #num = 1 and p.merchant_name <> #query then 0 else 1 end = 1
So here, CASE is used to return a value that can be tested in a comparison. There is no magic in using 0 or 1. Use any values of any type.
When #num is 1 and the values do NOT match, the THEN branch (0) is returned.
When #num is 1 and the values match, the ELSE branch (1) is returned.
When #num is anything but 1, the ELSE branch (1) is returned.
So when the CASE expression returns 0 (really - anything but 1), the row is ignored (removed from the resultset).
Given that your query is actually constructed in an application, you should considering dynamically building the query and adding parameters as needed. That will likely generate a more efficient query that can be better optimized by the database engine. Alternatively you can review this kitchen sink discussion and Erland's discussion of dynamic search conditions. TBH it looks like someone used #num as a kludge to avoid adding parameters for the eight specific filter values. If I want to filter on both merchant name and store name, I can't with this approach.
is there any alternative to case statement I want achieve below
*select
case when Etype=1 then 'Earthquake'
else 'Normal'
end
as Etype
something like this will do, although not sure what's the benefit of not using case:
select substring('EarthquakeNormal',power(sign(Etype-1),2)*11,11)
I'm assuming Etype is always >=0 if is >0 then the power is not required.
Also, please note that this solution is for SQL Server 2008 but from SQL Server 2012 onward there are at least another 3 better ways of doing it. IIF , choose and even parsename.
i have 2 dbs: one in mySql and one in MongoDB with the same data inside...
i do the follow in mySQL:
Select tweet.testo From tweet Where tweet.testo like ‘%pizza%’
and this is the result:
1627 rows in set (2.79 sec)
but if i exec in mongo:
Db.tweets.find({text: /pizza/ }).explain()
this is the result:
nscannedObjects" : 1606334,
"n" : 1169,
or if i exec:
Db.tweets.find({text: /pizza/i }).explain()
this is the result:
"nscannedObjects" : 1606334,
"n" : 1641,
Why the number of rows/document in mysql/mongo find is different?
Why the number of rows/document in mysql/mongo find is different??
There could be 1000000000000000 reasons including the temperature of the sun on that particular day.
MongoDB and MySQL are two completely separate techs as such if you expect to keep both in synch you will need some kind of replicator between the two. You have not made us aware as to whether this is the case.
Also we have no idea of your coding, server setup, network setup and everything else so really we cannot even begin to answer this.
A good answer would be to say that the reason you are seeing this is because the data between the two is different...
As for the difference between:
Db.tweets.find({text: /pizza/ }).explain()
and
Db.tweets.find({text: /pizza/i }).explain()
This is because MySQL, by default, queries in lower case I believe and MongoDB (I know) does not as such it is case sensitive (this i makes it case insensitive).
However about replicators, here is a good one: https://docs.continuent.com/wiki/display/TEDOC/Replicating+from+MySQL+to+MongoDB
the mysql command
Select tweet.testo From tweet Where tweet.testo like ‘%pizza%’
is equivalent to MongoDB's
Db.tweets.find({text: /pizza/i })
I realized they both contain the same data, but in some cases the text in mysql was cut-off, so it resulted in less rows being returned.
To begin with your SQL query like '%pizza%' may not pickup entries that begin with the string 'pizza' because of the wildcard on the front. Try the following SQL query to rule out any syntactical differences with the matching logic in SQL and the Regex used by MongoDB
Select tweet.testo From tweet Where lower(tweet.testo) like ‘%pizza%’ or lower(tweet.testo) like ‘pizza%’
Disclaimer: I don't have mySQL in front of me just now so can't verify the leading wildcard behaviour described above, however this is consistent with other RDBMS so it's worth checking
I can do this in MySQL:
WHERE 1 AND 1 AND 1
How can i repeat it in MongoDB? What is MongoDB's equivalent for WHERE 1 ?
UPDATE:
So. I don't know how choose best answer ^^ and expanded question. As #mark-hillick noticed - i'm searching the best way to build query.
Now I'm using this way (express+mongoose):
//req.query - get/post object in Express
for (var q in req.query) {
if (req.query[q]) { //simplified example
query[q] = req.query[q];
};
}
Collection.find(query)
Your suggestions?
There is a SQL-MongoDB Mapping Chart here that you will find useful.
It has a tonne of examples on what you do within MongoDB when you want to do the same operation as "WHERE" in MySQL. For example -
SELECT a,b FROM users WHERE age=33
is
db.users.find({age:33}, {a:1,b:1})
or
SELECT * FROM users WHERE a=1 and b=1
is
db.users.find({a:1,b:1})
MongoDB is document oriented database and documents in MongoDB consists key-value pairs. So, in MongoDB you can't run single value query as you did in MySql. Assuming you hold your data in the field name a, similar query in MongoDB could be like :
db.test.find({$and : [{a:1},{a:1}, {a:1}]});
If' you're trying to build query clauses, AND is implicit in Mongo. Therefore, if you have the following;
db.col.find({name:"dave"})
you could just add another;
db.col.find({name:"dave", age:33})
and so on.
How do I convert the following into MongoDB query ?
sets_progress = Photo.select('count(status) as count, status, photoset_id')
.where('photoset_id IN (?)', sets_tracked_array)
.group('photoset_id, status')
There is no 1 to 1 mapping of a SQL query to a NoSQL implementation. You'll need to precalculate your data to match the way you want to access that data.
If it is small enough, then this query will need to change into a map-reduce job. More here: http://www.mongodb.org/display/DOCS/MapReduce
Here's a decent tutorial that takes a query that GROUP's and converts to map-reduce: http://www.mongovue.com/2010/11/03/yet-another-mongodb-map-reduce-tutorial/