How can I insert a key-value pair into a hive map?

问题:

Based on the following tutorial, Hive has a map type. However, there does not seem to be a documented way to insert a new key-value pair into a Hive map, via a SELECT with some UDF or built-in function. Is this possible?

As a clarification, suppose I have a table called foo with a single column, typed map, named column_containing_map.

Now I want to create a new table that also has one column, typed map, but I want each map (which is contained within a single column) to have an additional key-value pair.

A query might look like this:

CREATE TABLE IF NOT EXISTS bar AS
SELECT ADD_TO_MAP(column_containing_map, "NewKey", "NewValue") 
FROM foo;

Then the table bar would contain the same maps as table foo except each map in bar would have an additional key-value pair.

回答1:

Consider you have a student table which contains student marks in various subjects.

hive> desc student;
id                      string
name                    string
class                    string
marks                   map<string,string>

You can insert values directly to table as below.

INSERT INTO TABLE student
SELECT STACK(1,
'100','Sekar','Mathematics',map("Mathematics","78")
)
FROM empinfo 
LIMIT 1;

Here 'empinfo' table can be any table in your database. And Results are:

100     Sekar   Mathematics     {"Mathematics":"78"}

回答2:

I'm sorry, I didn't quite get this. What do you mean by with some UDF or built-in function?If you wish to insert into a table which has a Map field it's similar to any other datatype. For example :

I have a table called complex1, created like this :

CREATE TABLE complex1(c1 array<string>, c2 map<int,string> ) ROW FORMAT DELIMITED FIELDS TERMINATED BY ',' COLLECTION ITEMS TERMINATED BY '-' MAP KEYS TERMINATED BY ':' LINES TERMINATED BY '\n';

I also have a file, called com.txt, which contains this : Mohammad-Tariq,007:Bond

Now, i'll load this data into the above created table :

load data inpath '/inputs/com.txt' into table complex1;

So this table contains :

select * from complex1;

OK

["Mohammad","Tariq"] {7:"Bond"}

Time taken: 0.062 seconds

I have one more table, called complex2 :

CREATE TABLE complex2(c1 map<int,string>);

Now, to select data from complex1 and insert into complex2 i'll do this :

insert into table complex2 select c2 from complex1;

Scan the table to cross check :

select * from complex2;

OK

{7:"Bond"}

Time taken: 0.062 seconds

HTH

回答3:

I think the combine function from brickhouse will do what you need. Slightly modifying the query in your original question, it would look something like this

SELECT 
    combine(column_containing_map, str_to_map("NewKey:NewValue")) 
FROM 
    foo;

The limitation with this example is that str_to_map creates a MAP< STRING,STRING >. If your hive map contains other primitive types for the keys or values, this won't work.