Oracle Merge vs Select然后选择Insert或Update

Question

什么更快？

合并声明

    MERGE INTO table_name 
     USING dual
     ON (row_id = 'some_id')
    WHEN MATCHED THEN
     UPDATE SET col_name = 'some_val'
    WHEN NOT MATCHED THEN
     INSERT (row_id, col_name)
     VALUES ('some_id', 'some_val')

要么

查询select语句然后使用update或insert语句.

    SELECT * FROM table_name where row_id = 'some_id'

如果rowCount == 0

    INSERT INTO table_name (row_id,col_name) VALUES ('some_id','some_val')

其他

    UPDATE table_name SET col_name='some_val' WHERE row_id='some_id'

Answer 1

的经验法则是,如果你可以在一个SQL做到这一点,它通常会先进行比多个SQL语句做得更好.

如果能做到这一点,我会选择MERGE.

另外 - 另一个建议:你可以避免在你的陈述中重复数据,例如:

MERGE INTO table
 USING (SELECT 'some_id' AS newid,
               'some_val' AS newval
        FROM dual)
 ON (rowid = newid)
WHEN MATCHED THEN
 UPDATE SET colname = newval
WHEN NOT MATCHED THEN
 INSERT (rowid, colname)
 VALUES (newid, newval)