How different is this to creating a primary key on

问题:

I read that we cannot create a primary key on a column in a Hive table. But I saw the below DDL in some other place and executed it. It worked without any problem.

create table prim(id int, name char(30))
TBLPROPERTIES("PRIMARY KEY"="id");

After this I executed "describe formatted prim" and got to see that a key is created on the column ID

Table Parameters:        
PRIMARY KEY             id        

I inserted two records with same ID number into the table.

insert into prim values(1,'ABCD');
insert into prim values(2,'EFGH');

Both the records were inserted into the table. What baffles me is that we cannot give the PRIMARY KEY in the create statement which I can understand, but when given in TBLPROPERTIES("PRIMARY KEY"="id") how different is it to the primary key in RDBMS.

回答1:

PRIMARY KEY in TBLPROPERTIES is for metadata reference to preserve column significance. It does not apply any constrain on that column. This can be used as a reference from design perspective.