How to add primary key to View?

Question

I have a view and want to make one attribute a primary key.

CREATE VIEW filedata_view AS SELECT num PRIMARY KEY, id, ST_TRANSFORM(the_geom,900913) AS the_geom FROM filedata 

But get a error

ERROR:  syntax error at or near "PRIMARY" LINE 2: AS SELECT num PRIMARY KEY, id, ST_TRANSFORM(the_geom,900913)... 

How to do this?

Answer 1

Views in Postgresql can't have primary keys.

you are basically on wrong way creating constraint on a View, constraints should be created on tables, but some DBMSes do support adding constraints on Views like oracle with this syntax:

ALTER VIEW VIEW_NAME ADD PRIMARY KEY PK_VIEW_NAME DISABLE NOVALIDATE; 

Oracle Doc For Constraints

You can specify only unique, primary key, and foreign key constraints on views, and they are supported only in DISABLE NOVALIDATE mode.

so they only support it for compatibility, if you want to have a primary key to stop insertion of duplicate data in column num in filedata table, you should do it by altering the filedata table and add a primary key on it or by creating your table with primary key on column num from the start.