SPI_register_trigger_data — make ephemeral trigger data available in SPI queries
int SPI_register_trigger_data(TriggerData *tdata)   SPI_register_trigger_data makes any ephemeral
   relations captured by a trigger available to queries planned and executed
   through the current SPI connection.  Currently, this means the transition
   tables captured by an AFTER trigger defined with a
   REFERENCING OLD/NEW TABLE AS ... clause.  This function
   should be called by a PL trigger handler function after connecting.
  
TriggerData *tdata       the TriggerData object passed to a trigger
       handler function as fcinfo->context
     
If the execution of the command was successful then the following (nonnegative) value will be returned:
SPI_OK_TD_REGISTERif the captured trigger data (if any) has been successfully registered
On error, one of the following negative values is returned:
SPI_ERROR_ARGUMENT       if tdata is NULL
      
SPI_ERROR_UNCONNECTEDif called from an unconnected procedure
SPI_ERROR_REL_DUPLICATEif the name of any trigger data transient relation is already registered for this connection