在PostgreSQL中,可以通过Explain输出来确定是否仅进行索引扫描。Explain是一个用于分析查询计划的工具,它可以显示查询语句的执行计划和相关的统计信息。 要确定是否仅进行索引扫描,可...
AI代码解释 mysql>explain format=treeSELECT*FROMt1WHEREt1.aIN(SELECTt2.bFROMt2WHEREid<10);***1.row***->Nested loop innerjoin(cost=4.95rows=9)->Filter:(`<subquery2>`.b is notnull)(cost=2.83..1.80rows=9)->Table scan on<subquery2>(cost=0.29..2.61rows=9)->Materializewithdeduplication...
查询时不需要回表查询,直接通过索引就可以获取查询的数据。 using join buffer(block nestedloop),using join buffer(batched key accss): 5.6.x之后的版本优化关联查询的BNL,BKA特性。主要是减少内表的循环数量以及比较顺序地扫描查询。 using sort_union,using_union,usingintersect,using sort_intersection: using ...
-> Nested loop inner join (cost=49828 rows=76470) (actual time=1.95..5182 rows=227103 loops=1) -> Filter: ((orders.quantity > 1000) and (orders.item_id is not null)) (cost=23063 rows=76470) (actual time=1.82..1271 rows=227103 loops=1) -> Table scan on orders (cost=23063 rows...
Block Nested Loop,需要进行嵌套循环计算。两个关联表join,关联字段均未建立索引,就会出现这种情况。比如内层和外层的type均为ALL,rows均为4,需要循环进行4*4次计算。常见的优化方案是,在关联字段上添加索引,避免每次嵌套循环计算。 本文参考了一些优秀的博客,感兴趣的可以了解下: ...
id": 1, # 整个查询语句只有1个SELECT关键字,该关键字对应的id号为1 "cost_info": { "query_cost": "3197.16" # 整个查询的执行成本预计为3197.16 }, "nested_loop": [ # 几个表之间采用嵌套循环连接算法执行 # 以下是参与嵌套循环连接算法的各个表的信息 { "table": { "table_name": "s1", # ...
| -> Nested loop inner join (cost=4505.00 rows=10000) -> Table scan on b (cost=1005.00 rows=10000) -> Single-row covering index lookup on a using PRIMARY (id=) (cost=0.25 rows=1) | +---+ 1 row in set (0.00 sec) 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 执行计划显示NL j...
F:using join buffer(block nested loop),using join buffer(batched key accss):5.6.x之后的版本优化关联查询的BNL,BKA特性。主要是减少内表的循环数量以及比较顺序地扫描查询。 G:using sort_union,using_union,using intersect,using sort_intersection: ...
ng-form and ng-submit in a ng-repeat I have been trying to get a nested form to validate properly and then call a function on my controller when the submit button is clicked. I have tried remove all buttons except the submit button and i... ...
where 'i' is the loop variable The 'do-while' loop can be implemented (in C) as: inti=5; do { printf("%d",i); i--; }while(i>=0); where 'i' is the loop variable. Answer and Explanation:1 Both for loop and while loop can run multiple statements in successive repetition effic...