pg_query() returns a query result resource if query could be executed. It returns FALSE on failure or if connection is not a valid connection. Details about the error can be retrieved using the pg_last_error() function if connection is valid. pg_last_error() sends an SQL statement to the PostgreSQL database specified by the connection resource. The connection must be a valid connection that was returned by pg_connect() or pg_pconnect(). The return value of this function is an query result resource to be used to access the results from other PostgreSQL functions such as pg_fetch_array().
Although connection can be omitted, it is not recommended, since it could be a cause of hard to find bug in script.
Note: This function used to be called pg_exec(). pg_exec() is still available for compatibility reasons but users are encouraged to use the newer name.