E:using index: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。 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 so...
Using join buffer : 使用了连接缓存,Block Nested Loop,连接算法是块嵌套循环连接;Batched Key Access,连接算法是批量索引连接。 Using where : 表示 MySQL 服务器从存储引擎收到查询数据,再进行 “后过滤”(Post-filter)。所谓 “后过滤”,就是先读取整行数据,再检查此行是否符合 where 句的条件,符合就留下...
他俩之间只是一个order by不同,MySQL 表关联的算法是 Nest Loop Join,是通过驱动表的结果集作为循环基础数据,然后一条一条地通过该结果集中的数据作为过滤条件到下一个表中查询数据,然后合并结果。EXPLAIN 结果中,第一行出现的表就是驱动表(Important!)以上两个查询语句,驱动表都是 city,如上面的执行计划所示!
If the EXPLAIN ANALYZE output shows high execution time or slow node types (e.g., Seq Scan on large tables), it suggests potential areas for optimization, such as adding indexes. EXPLAIN ANALYZE also highlights inefficiencies in query structure, join types, or filtering methods, which can be ...
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Key Concepts in Query Plans: Sequential Scan:A full table scan, generally slower for large tables. Index Scan:Faster for selective queries, leveraging an index. Nested Loop, Hash Join, Merge Join:Join types that PostgreSQL chooses based on data and index availability. ...
In fact, it's not a bug that occurs only in debug builds. In release-builds, `explain format=tree for conn` at sync point BEFORE_RESET_QUERY_PLAN gives incorrect query plan. Take the same query in the test case as an example, the correct plan (from explain <query>) is: ``` ->...
The main reason I'm asking this question is because I set-up a video stream using ESP-IDF HTTP Server and I also wanted to obtain the camera frames myself in the Arduino loop function to process video frames independently of the server. So I have two separate calls toesp_camera_fb_get...
The comic does not work in many Linux versions.Tree trunks will sometimes grow endlessly without leaves depending on the lights hitting them.If you are dragging a light, the arrow, or the color slider when a refresh happens, the refresh will enter an infinite loop. This seems to corrupt ...
For example, sine(x) returns 1 when x is 90°. Furthermore, the function may call itself (usually with slightly different parameters), thus effectively starting a loop. This is called recursion. In order to iterate, imperative programs usually use loops. Functional programs usually use ...