Mybatis XML 数据源为 Oracle 之批量插入或更新 Merge Into 的具体介绍与使用
文章目录
- 声明
- 一、前言
- 1、MergeInto简介
- 2、MergeInto批量插入更新
- 3、带有CLOB类型字段的MergeInto
声明
- 原文地址:https://blog.csdn.net/qq_42142477/article/details/115198285
一、前言
- 由于近期在所开发的项目中,对于数据入库,有 存在即更新,不存在则插入 的需求,因此发现了 Oracle中的 MergeInto 命令。本文将对MergeInto的用法进行介绍并将 MergeInto 和批量插入进行结合,同时还会对在 MergeInto 开发中遇到的问题进行总结。
1、MergeInto简介
-
MergeInto 命令是 Oracle9i 中新增的命令,有了 MergeInto 语句,我们对数据能够不仅仅只做单一的插入或单一的更新,而是可以将更新与插入一起操作。
-
MergeInto通过对两张表进行连接比较,如果匹配则 UPDATE,否则 INSERT
语法
MERGE INTO table_name a
USING ((table|view|sub_query)
) b
ON (condition)
WHEN MATCHED THENmerge_update
WHEN NOT MATCHED THENmerge_insert
举例
MERGE INTO USER a
USING (select * from USER
) b
ON (condition)
WHEN MATCHED THENmerge_update
WHEN NOT MATCHED THENmerge_insert
- 注意
- 此处的update语句与平时我们写的update语句不同,update和set之间不能有表名,否则会报缺少SET关键字。
- update语句中不能存在在ON中进行匹配后的字段,否则会报无法更新 ON 子句中引用的列A.USERID。
错误❌:
MERGE INTO USER a
USING (select #{user.userid} as id from dual
) b
ON (a.USER_ID = b.id)
WHEN MATCHED THENUPDATE SET USER USER_ID = b.idUSER_NAM = b.usernameWHERE USER_ID = b.userid
WHEN NOT MATCHED THENmerge_insert
正确✔:
MERGE INTO USER a
USING (select #{user.userid} as id from dual
) b
ON (a.USER_ID = b.userid)
WHEN MATCHED THENUPDATE SET USER USER_NAM = b.usernameWHERE USER_ID = b.userid
WHEN NOT MATCHED THENmerge_insert
- update语句中不能在update中使用ON连接条件中的命名,否则会报B.USERID标识符无效。
错误❌:
MERGE INTO USER a
USING (select #{user.userid} as id from dual
) b
ON (a.USER_ID = b.userid)
WHEN MATCHED THENUPDATE SET USER USER_ID = b.useridUSER_NAM = b.usernameWHERE USER_ID = b.userid
WHEN NOT MATCHED THENmerge_insert
正确✔:
MERGE INTO USER a
USING (select #{user.userid} as id from dual
) b
ON (a.USER_ID = b.userid)
WHEN MATCHED THENUPDATE SET USER USER_NAM = b.usernameWHERE USER_ID = b.userid
WHEN NOT MATCHED THENmerge_insert
- 关于MergeInto只能更新不能插入(Updates:0)
merge into a using on b,a、b表进行比较
情况 | 结果 |
---|---|
a存在,b不存在 | nothing |
a存在,b存在 | update |
a不存在,b存在 | insert b into a |
a不存在,b不存在 | nothing |
错误❌:如果是第一次入库,b必然为null
MERGE INTO USER a
USING (select #{user.userid} as id from USER
) b
ON (a.USER_ID = b.userid)
WHEN MATCHED THENUPDATE SET USER USER_ID = b.useridUSER_NAM = b.usernameWHERE USER_ID = b.userid
WHEN NOT MATCHED THENmerge_insert
正确✔:
MERGE INTO USER a
USING (select #{user.userid} as id from dual
) b
ON (a.USER_ID = b.userid)
WHEN MATCHED THENUPDATE SET USER USER_NAM = b.usernameWHERE USER_ID = b.userid
WHEN NOT MATCHED THENmerge_insert
2、MergeInto批量插入更新
- 我们已经知道批量入库是将一个list作为整体进行入库操作,那么MergeInto和批量入库结合起来应该怎么写呢?又会有什么问题?
传统的批量入库
insert into USER(
USER_ID,USER_NAM
)
<foreach collection="list" item="item" index="index" separator="union all">(SELECT#{item.userid},#{item.username}FROM DUAL)
</foreach>
MergeInto批量
MERGE INTO USER a
USING (<foreach collection="list" item="item" index="index" separator="union all">(SELECT#{item.userid,jdbcType=VARCHAR} as userid,#{item.username,jdbcType=VARCHAR} as usernameFROM DUAL)</foreach>
) b
ON (a.USER_ID = b.userid)
WHEN MATCHED THENUPDATE SET USER USER_NAM = b.usernameWHERE USER_ID = b.userid
WHEN NOT MATCHED THENINSERT(USER_ID,USER_NAM)VALUES(b.userid,b.username)
)
注意
- 采取批量入库的时候,同一批的数据无法进行存在更新,不存在插入。因为同一批的数据不在比较范围内。
- 解决方法:目前我还没有找到怎么在数据库语句中进行优化解决,但是我们可以在代码逻辑中,对list进行一个判断,如果已存在,则不执行list.add()。通过代码和数据库结合的方法,就可以避免上述情况了。
3、带有CLOB类型字段的MergeInto
-
如果说我们将带有CLOB类型字段的sql按照上述语句去写,代码执行过程中会报错:java.sql.SQLSyntaxErrorException:ORA-01790:表达式必须具有对应表达式相同的数据类型。
-
因此,针对带有CLOB类型字段的sql有两种写法:
-
写法1
begin<foreach collection="list" item="item" index="index">MERGE INTO USER aUSING (SELECT#{item.userid,jdbcType=VARCHAR} as userid,#{item.username,jdbcType=CLOB} as usernameFROM DUAL)bON (a.USER_ID = b.userid) WHEN MATCHED THENUPDATE SET USER USER_NAM = b.usernameWHERE USER_ID = b.useridWHEN NOT MATCHED THENINSERT(USER_ID,USER_NAM)VALUES(b.userid,b.username);</foreach>
end;
- 写法2
- 将empty_clob()代替要插入的clob数据,再用真正的数据去替换empty_clob()
- 注意: 要对clob字段进行非空判断,不然当clob为空时会报错
begin<foreach collection="list" item="item" index="index">MERGE INTO USER aUSING (SELECT#{item.userid,jdbcType=VARCHAR} as userid,empty_clob() as usernameFROM DUAL)bON (a.USER_ID = b.userid) WHEN MATCHED THENUPDATE SET USER USER_NAM = b.usernameWHERE USER_ID = b.useridWHEN NOT MATCHED THENINSERT(USER_ID,USER_NAM)VALUES(b.userid,b.username);<if test="item.vluResume != null">update USER set USER_NAM = #{item.username,jdbcType=CLOB} where USER_ID = #{item.userid,jdbcType=VARCHAR} ;</if></foreach>
end;