Merge into 的用法

原型：

MERGE INTO table_name alias1 
USING (table|view|sub_query) alias2
ON (join condition) 
WHEN MATCHED THEN 
    UPDATE table_name 
    SET col1 = col_val1, 
           col2 = col_val2 
WHEN NOT MATCHED THEN 
    INSERT (column_list) VALUES (column_values); 

实例：

MERGE INTO T T1
USING (SELECT '1001' AS a,2 AS b FROM dual) T2
ON ( T1.a=T2.a)
WHEN MATCHED THEN
    UPDATE SET T1.b = T2.b
WHEN NOT MATCHED THEN 
    INSERT (a,b) VALUES(T2.a,T2.b);