I am new to Presto, and can't quite figure out how to check if a key is present in a map. When I run a SELECT query, this error message is returned:
Key not present in map: element
SELECT value_map['element'] FROM
mytable
WHERE name = 'foobar'
Adding AND contains(value_map, 'element') does not work
The data type is a string array
SELECT typeof('value_map') FROM mytable
returns varchar(9)
How would I only select records where 'element' is present in the value_map?
You can lookup a value in a map if the key is present with element_at, like this:
SELECT element_at(value_map, 'element')
FROM ...
WHERE element_at(value_map, 'element') IS NOT NULL
element_at is ambiguous in that case -- it'll return NULL when either there's no such key or the key does exist and has NULL associated with it. A guaranteed approach is contains(map_keys(my_map), 'mykey'), which admittedly should be a bit slower than the original variant.
Related
I have one table TestTable and partition Key TestColumn.
Inputs Dates:
from_date= "2017-04-20T16:31:54.451071+00:00"
to_date = "2018-04-20T16:31:54.451071+00:00"
when I use equal query the date then it is working.
key_expr = Key('TestColumn').eq(to_date)
query_resp = table.query(KeyConditionExpression=key_expr)
but when I use between query then is not working.
key_expr = Key('TestColumn').between(from_date, to_date)
query_resp = table.query(KeyConditionExpression=key_expr)
Error:
Unknown err_msg while querying dynamodb: An error occurred (ValidationException) when calling the Query operation: Query key condition not supported
https://docs.aws.amazon.com/amazondynamodb/latest/APIReference/API_Query.html
DynamoDB Query will return data from one and only one partition, meaning you have to supply a single partition key in the request.
KeyConditionExpression
The condition that specifies the key value(s)
for items to be retrieved by the Query action.
The condition must perform an equality test on a single partition key
value.
You can optionally use a BETWEEN operator on a sort key (but you still have to supply a single partition key).
If you use a Scan you can use an ExpressionFilter and use the BETWEEN operator on TestColumn
I am currently working on a Cassandra 3 database in which one of its tables has a column that is defined like this:
column_name map<int, frozen <set<int>>>
When I have to change the value of a complete set given a map key x I just have to do this:
UPDATE keyspace.table SET column_name[x] = {1,2,3,4,5} WHERE ...
The thing is that I need to insert a value on a set given a key. I tried with this:
UPDATE keyspace.table SET column_name[x] = column_name[x] + {1} WHERE ...
But it returns:
SyntaxException: line 1:41 no viable alternative at input '[' (... SET column_name[x] = [column_name][...)
What am I doing wrong? Does anyone know how to insert data the way I need?
Since the value of map is frozen, you can't use update like this.
A frozen value serializes multiple components into a single value. Non-frozen types allow updates to individual fields. Cassandra treats the value of a frozen type as a blob. The entire value must be overwritten.
You have to read the full map get the value of the key append new item and then reinsert
I am trying to insert values in UDT but getting error message -
message="unconfigured columnfamily my_object"
below my statement-
INSERT INTO home.my_object (id,type,quantity ,critical,page_count,stock,outer_envelope ) VALUES ('3.MYF','COM','D','A','VV','','');
What am i doing wrong?
That error means that the keyspace "home" exists, but does not contain a table (column family) called "my_object". I also noticed that your insert statement does not contain a UDT literal.
UDTs define a type, but you must also define a table with a column of that type before inserting any data. I assume your UDT is called "my_object". Try this:
create table home.test (key int primary key, object frozen<my_object>);
insert into home.test (key, object) values (0, {id: 'value', type: 'othervalue'});
In my cassandra table i have a collection of Map also i have indexed the map keys.
CREATE TABLE IF NOT EXISTS test.collection_test(
name text,
year text,
attributeMap map<text,text>,
PRIMARY KEY ((name, year))
);
CREATE INDEX ON collection_test (attributeMap);
The QueryBuilder syntax is as below:
select().all().from("test", "collection_test")
.where(eq("name", name)).and(eq("year", year));
How should i put where condition on attributeMap?
First of all, you will need to create an index on the keys in your map. By default, an index created on a map indexes the values of the map, not the keys. There is special syntax to index the keys:
CREATE INDEX attributeKeyIndex ON collection_test (KEYS(attributeMap));
Next, to SELECT from a map with indexed keys, you'll need the CONTAINS KEY keyword. But currently, there is not a definition for this functionality in the query builder API. However, there is an open ticket to support it: JAVA-677
Currently, to accomplish this with the Java Driver, you'll need to build your own query or use a prepared statement:
PreparedStatement statement = _session.prepare("SELECT * " +
"FROM test.collection_test " +
"WHERE attributeMap CONTAINS KEY ?");
BoundStatement boundStatement = statement.bind(yourKeyValue);
ResultSet results = _session.execute(boundStatement);
Finally, you should read through the DataStax doc on When To Use An Index. Secondary indexes are known to not perform well. I can't imagine that a secondary index on a collection would be any different.
i'm using cassandra 1.2.8. i have a column family like below:
CREATE TABLE word_probability (
word text,
category text,
probability double,
PRIMARY KEY (word,category)
);
when i use query like this:
String query = "SELECT * FROM word_probability WHERE word='%s' AND category='%s';";
it works well but for some words i get this message:
name provided was not in the list of valid column labels error
every thing is ok and i don't know why i get this error :(
You're not doing anything wrong except mixing up cql with sql. Cql doesn't support % wildcards.