使用NOT EXISTS方式SQL为: SELECTcount(1)FROMt_monitor mWHERENOTexists(SELECT1FROMt_alarm_realtimeASaWHEREa.resource_id=m.resource_idANDa.resource_type=m.resource_typeANDa.monitor_name=m.monitor_name) 而使用LEFT JOIN方式
NOT IN、JOIN、IS NULL、NOT EXISTS效率对比 语句一:select count(*) from A where A.a not in (select a from B) 语句二:select count(*) from A left join B on A.a = B.a where B.a is null 语句三:select count(*) from A where not exists (select a from B where A.a = B.a) ...
NOT EXISTS以更直观地方式实现业务需求，在SQL复杂度上要远低于LEFT JOIN，且在生产执行计划时，NOT EXI...
由于客户数据量越来越大,在实践中让我发现mysql的exists与inner join 和 not exists与 left join 性能差别惊人。 我们一般在做数据插入时,想插入不重复的数据,或者盘点数据在一个表,另一个表否有存在相同的数据会用not exists和exists,例如: insert into t1(a1) select b1 from t2 where not exists(select 1 ...
NOT IN、JOIN、IS NULL、NOT EXISTS效率对比 语句一:select count(*) from A where A.a not in (select a from B) 语句二:select count(*) from A left join B on A.a = B.a where B.a is null 语句三:select count(*) from A where not exists (select a from B where A.a = B.a) ...
WHERE NOT EXISTS (SELECT 1 FROM tableB B WHERE A.id = B.id); 1. 2. 3. 4. 通过NOT EXISTS 子查询,进一步过滤出最终符合条件的结果。 3. 表关系图 通过以上步骤和代码示例,你应该可以实现“mysql not in left join IS NULL NOT EXISTS 效率问题记录”的功能了。如果有任何疑问,欢迎随时向我提问。
mysqlnotin、leftjoin、ISNULL、NOTEXISTS效率问题记 录 语句⼀：select count(*) from A where A.a not in (select a from B)语句⼆：select count(*) from A left join B on A.a = B.a where B.a is null 语句三：select count(*) from A where not exists (select a from B where A....
NOT IN、JOIN、IS NULL、NOT EXISTS效率对比 语句一:select count(*) from A where A.a not in (select a from B) 语句二:select count(*) from A left join B on A.a = B.a where B.a is null 语句三:select count(*) from A where not exists (select a from B where A.a = B.a) ...
NOT EXISTSperforms in most straightforward way: just checks equality and returnsTRUEorFALSEon the first hit / miss. LEFT JOIN / IS NULLeither makes an additional table lookup or does not return on the first match and performs more poorly in both cases. ...
3. 使用 not in 语句时,也不能走索引。举个例子 : select*fromtb_staffwhereid_nonotin('xxxx','yyyy'); 4. 使用 not exists 语句时,也不能走索引。举个例子 :再建一张专门保存 staff_id 的表 db_staff_id SELECT*FROMdb_staff fWHERENOTEXISTS(SELECTstaff_idFROMdb_staff_id aWHEREa.staff_id ...