Bug # 16519 [1] is another report of confusion regarding trying to use parameters in improper locations - specifically the SET ROLE command within pl/pgsql. I'm re-attaching the doc patch and am adding it to the commitfest.
I checked this patch, and I think so it is correct - my comments are just about enhancing by some examples
Maybe for following sentence the some examples can be practical
+ If the SQL command being executed is incapable of returning a result + it does not accept query parameters. </para>
+ it does not accept query parameters (usually DDL commands like CREATE TABLE, DROP TABLE, ALTER ... ).
+ Query parameters will only be substituted in places where syntactically allowed + (in particular, identifiers can never be replaced with a query parameter.) + As an extreme case, consider this example of poor programming style:
In this case, I miss the more precious specification of identifiers
+ (in particular, SQL identifiers (like schema, table, column names) can never be replaced with a query parameter.)
