if ( exists ( select null from t2 where y = x.x ) then OUTPUT THE RECORD! end if end loop ——这个更容易理解,t1永远是个表扫描!因此t1绝对不能是个大表,而t2可以很大,因为y=x.x可以走t2.y的索引。 综合以上对IN/EXISTS的讨论,我们可以得出一个基本通用的结论:IN适合于外表大而内表小的情况;EXISTS适合于外表小而内表...
not in 逻辑上不完全等同于not exists,如果你误用了not in,小心你的程序存在致命的BUG,请看下面的例子: 代码语言:javascript 代码运行次数:0 运行 AI代码解释 create table#t1(c1 int,c2 int);create table#t2(c1 int,c2 int);insert into #t1values(1,2);insert into #t1values(1,3);insert into #t2...
for x in ( select * from t1 ) loop if ( exists ( select null from t2 where y = x.x ) then OUTPUT THE RECORD end if end loop 对于in 和 exists的性能区别: 如果子查询得出的结果集记录较少,主查询中的表较大且又有索引时应该用in,反之如果外层的主查询记录较少,子查询中的表大,又有索引...
2、not in 和not exists not in 逻辑上不完全等同于not exists,如果你误用了not in,小心你的程序存在致命的BUG,请看下面的例子: create table #t1(c1 int,c2 int); create table #t2(c1 int,c2 int); insert into #t1 values(1,2); insert into #t1 values(1,3); insert into #t2 values(1,2...
if ( exists ( select null from t2 where y = x.x ) then OUTPUT THE RECORD end if end loop 对于in 和 exists的性能区别: 如果子查询得出的结果集记录较少,主查询中的表较大且又有索引时应该用in,反之如果外层的主查询记录较少,子查询中的表大,又有索引时使用exists。
insertintoexam_record(uid,exam_id,start_time,submit_time,score) VALUE (1001,9001,'2021-09-01 22:11:12','2021-09-01 23:01:12',90); 1. 2. 3. 插入记录:SQL111 插入记录(二) 初始化数据 droptableif EXISTS exam_record; CREATETABLEIFNOTEXISTS exam_record( ...
问错误: SQL命令中不存在列“exist”ENSQL是IT行业很多岗位都要求具备的一项能力，对于数据岗位而言更是...
Also in some cases only an insert is required if record doesnt exist, the basic if not exists(select) insert , will work best but if most of the time update is expected the way you mentioned works better. Had been using these for past few months and one of my friend Just stumbled on...
to be updated if it already exists and inserted if it does not. If we refer to the Books Online documentation, it gives examples that are similar to: IF EXISTS (SELECT * FROM Table1 WHERE Column1='SomeValue') UPDATE Table1 SET (...) WHERE Column1='SomeValue' ELSE INSERT INTO Table...
解决方法:去掉RETURNING,仅使用INSERT ON CONFLICT语法,详情请参见INSERT ON CONFLICT(UPSERT)。 报错:ERROR: INSERT in ddl transaction is not supported now 问题原因:不支持在事务中使用INSERT。示例如下: BEGIN;INSERTxxxcommit; ERROR:INSERTinddl transactionisnotsupported now ...