Difference between Teradata Primary Index and Primary Key

If you have worked on other RDBMS then you must be aware of Primary KEY concept. In Teradata ,Primary Key does not play as important role as Primary INDEX. In this post, we will see difference between Primary Key and Primary Index.

One must not get confused between Primary Key and Primary Index in Teradata. Primary KEY is more of a logical thing however Primary INDEX is more of physical thing. In Teradata, Primary INDEX is used for finding best access path for data retrieval and data insertion and Primary KEY is used for finding each rows uniquely just like in other RDBMS.

5 differences between PRIMARY KEY and PRIMARY INDEX

#	PRIMARY KEY	PRIMARY INDEX
1	PRIMARY KEY cannot be NULL	PRIMARY INDEX can be NULL
2	PRIMARY KEY is not mandatory in Teradata	PRIMARY INDEX is mandatory in Teradata with exception of NOPI tables
3	PRIMARY KEY does not help in data distribution.	PRIMARY INDEX helps in data distribution
4	PRIMARY KEY should be unique.	PRIMARY INDEX can be UNIQUE (Unique Primary Index) or NON UNIQUE (Primary Index).
5	PRIMARY KEY is logical implementation.	PRIMARY INDEX is physical implementation.

Now we will see few scenarios to see how these two are handled in Teradata

I have not defined PRIMARY INDEX or PRIMARY KEY on table what will happen now

In this case, Teradata will check if any column is defined as UNIQUE, then it will make that column as UNIQUE PRIMARY INDEX else first column will be created as PRIMARY INDEX.

I have not defined PRIMARY INDEX however a column is defined as PRIMARY KEY

In this case, Teradata will make the PRIMARY KEY column as UNIQUE PRIMARY INDEX of the table.

I have defined both PRIMARY KEY and PRIMARY INDEX on different column

In this case, Teradata will make PRIMARY KEY column as UNIQUE SECONDARY INDEX i.e. UNIQUE INDEX on the table.

So one must understand the importance of PRIMARY INDEX in Teradata. Generally, PRIMARY KEY concept is taken care by UNIQUE PRIMARY INDEX in Teradata environment.

what is the difference between primary key and unique key

Similar to primary key , you can define column as UNIQUE which will enforce unique value for the column. The difference is you can have multiple columns in the table defined as UNIQUE however a table can have only one primary key.