REPLACE INTO 语句会判断行记录是否存在（根据主键索引或唯一索引判断）。如果不存在，则插入记录；如果存在，则删除已有记录，并插入新行记录。目标表建议有主键或者唯一索引，否则容易插入重复的记录。

    示例如下：

    1. obclient> CREATE TABLE t_replace(
    2.      id number NOT NULL PRIMARY KEY
    3.      , name varchar(10) NOT NULL
    4.      , value number
    5.      ,gmt_create timestamp NOT NULL DEFAULT current_timestamp
    6.  );
    7. Query OK, 0 rows affected (0.06 sec)
    9. obclient> REPLACE INTO t_replace values(1,'CN',2001, current_timestamp ());
    10. Query OK, 1 row affected (0.00 sec)
    12. obclient> REPLACE INTO t_replace
    13.      SELECT id,name,value,gmt_create  FROM t_insert;
    14. Query OK, 5 rows affected (0.00 sec)
    15. Records: 4  Duplicates: 1  Warnings: 0
    17. obclient> REPLACE INTO t_replace(id, name, value)  values(6,'DE',20006);
    18. Query OK, 1 row affected (0.01 sec)
    20. obclient> select * from t_replace;
    21. +----+------+-------+---------------------+
    22. | id | name | value | gmt_create          |
    23. +----+------+-------+---------------------+
    24. |  1 | CN   | 10001 | 2020-04-03 16:05:45 |
    25. |  2 | US   | 10002 | 2020-04-03 16:05:54 |
    26. |  3 | UK   | 10003 | 2020-04-03 16:05:54 |
    27. |  4 | JP   | 10004 | 2020-04-03 16:06:08 |
    28. |  6 | DE   | 20006 | 2020-04-03 16:09:19 |
    29. +----+------+-------+---------------------+
    30. 5 rows in set (0.01 sec)