PostgreSQL11: psql 新增变量记录SQL语句的执行情况和错误

**ERROR**
true if the last SQL query failed, false if it succeeded. See also SQLSTATE.

**SQLSTATE**
The error code (see Appendix A) associated with the last SQL query is failure, or 00000 if it succeeded.

**ROW_COUNT**
The number of rows returned or affected by the last SQL query, or 0 if the query failed or did not report a row count.

**LAST_ERROR_MESSAGE**
**LAST_ERROR_SQLSTATE**
The primary error message and associated SQLSTATE code for the most recent failed query in the current psql session, or an empty string and 00000 if no error has occurred in the current session.

[pg11@pghost2 ~]$ psql francs francs
psql (11beta3)
Type "help" for help.

francs=> SELECT * FROM generate_series(1,3);
 generate_series
-----------------
               1
               2
               3
(3 rows)

francs=> \echo :ERROR
false

francs=> \echo :SQLSTATE
00000

francs=> \echo :ROW_COUNT
3

francs=> SELECT *,afcd FROM generate_series(1,3);
ERROR:  column "afcd" does not exist
LINE 1: SELECT *,afcd FROM generate_series(1,3);
                 ^
francs=> \echo :ERROR
true

francs=> \echo :SQLSTATE
42703

francs=> \echo :ROW_COUNT
0

francs=> \echo :LAST_ERROR_MESSAGE
column "afcd" does not exist

francs=> \echo :LAST_ERROR_SQLSTATE
42703