oracle中的replace into使用及说明

<update id="mergeStudents" parameterType="com.alibaba.dto.StudentDTO">
		merge into t_student a
		using
		(
			SELECT
			#{id} as id,
			#{name} as name,
			#{age} as age
			FROM dual
		) b
		on (
		a.id= b.id
		)
		when matched then
		UPDATE SET
		a.name= b.name,
		a.age=b.age
		when not matched then
		INSERT(
		a.id,
		a.name,
		a.age
		) VALUES(
		b.id,
		b.name,
		b.age
		)
	</update>

<update id="mergeStudents" parameterType="com.alibaba.dto.StudentDTO">
		merge into t_student a
		using
		(
		<foreach collection="stus" item="item" index="index" open=""
				 close="" separator="union all">
			SELECT
			#{item.id,jdbcType=VARCHAR} as id,
			#{item.name,jdbcType=VARCHAR} as name,
			#{item.age,jdbcType=VARCHAR} as age
			FROM dual
		</foreach>
		) b
		on (
		a.id= b.id
		)
		when matched then
		UPDATE SET
		a.name= b.name,
		a.age=b.age
		when not matched then
		INSERT(
		a.id,
		a.name,
		a.age
		) VALUES(
		b.id,
		b.name,
		b.age
		)
	</update>

MERGE INTO [your table-name] [rename your table here]  
USING ( [write your query here] )[rename your query-sql and using just like a table]  
ON ([conditional expression here] AND [...]...)  
WHEN MATHED THEN [here you can execute some update sql or something else ]  
WHEN NOT MATHED THEN [execute something else here ! ]  

merge into qq a  
using (select '2022' company_no, 'cname' company_name from qq where rownum<2) b  
on (a.company_no = b.company_no)  
WHEN MATCHED THEN  
  UPDATE SET a.company_name = a.company_name|| 'a'  
WHEN NOT MATCHED THEN  
  INSERT  
    (a.company_no, a.company_name)  
  VALUES  
    (b.company_no, b.company_name);