MySQL 语句级避免重复插入—— Insert Select Not Exist
Posted onMySQL 语句级避免重复插入—— Insert Select Not Exist
想要插入一条数据,要避免重复插入,又不想折腾两回数据库连接操作,可以参考如下办法。 Sql代码
- INSERT INTO table(column1,column2,column3 ...columnN)
- SELECT value1,value2,value3 ...valueN
- FROM dual
- WHERE NOT EXISTS(
- SELECT /*
- FROM table
- WHERE value = ?
- );
INSERT INTO table(column1,column2,column3 ...columnN)
SELECT value1,value2,value3 ...valueN FROM dual
WHERE NOT EXISTS( SELECT /*
FROM table
WHERE value = ?
); dual是为了构建查询语句而存在的表,Oracle中很常见,配合INSERT ... SELECT构建成我们需要的表,并指定了数据项. EXISTS通过这个判断是否存在的函数,就免去了我们做IF-ELSE的冗繁操作. 例: Sql代码
- INSERT INTO content (
- detail,
- status,
- beginTime,
- endTime)
- SELECT
- @detail,
- 1,
- NULL,
- NULL
- FROM DUAL
- WHERE NOT EXISTS(
- SELECT contentId
- FROM content
WHERE detail=@detail);
INSERT INTO content (
detail, status, beginTime, endTime)
SELECT
@detail, 1, NULL, NULL
FROM DUAL
WHERE NOT EXISTS(
SELECT contentId FROM content WHERE detail=@detail);
@detail是要存入的内容,这里对内容进行了检索,如果要这么做,最好对该字段做唯一约束,或加索引。 省掉了IF-ELSE,在iBatis配置一下就ok了,哈! 还有个更坚决的办法——replace into: Sql代码
replace into blacklist(userInfoId,uid)
- select userInfoId,uid from user_info u where uid in(
- 'u303565440','u303566922','u303515112','u303559738');
replace into blacklist(userInfoId,uid)
select userInfoId,uid from user_info u where uid in( 'u303565440','u303566922','u303515112','u303559738');