How does let in for loop work? I understand how "var" works and I'm quite used to it - the scope is functional. However the let statement is far from clear. I understand is has block scope, but why does THAT matter in the......
I have a node template in go.js with a "topArray" that might contain a several ports like in this example. For each top port I want to add a "controller" item - a small clickable r... what does the second www-data mean?
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 efficiently. ...
MYSQL explain 可没有那么简单,explain的猫腻与函数 explain 到底会不会执行命令着一点很多人应该是不置可否的任务,他不能执行命令,而仅仅是对语句进行评估然后反馈执行的计划。 我们创建一个函数 DELIMITER CREATEFUNCTIONinsertinto()RETURNSchar(50)CHARSETutf8DETERMINISTICBEGINinsertintotest(id)values(1),(2);RETUR...
mysql root@localhost:(none)>selectversion();+---+|version()|+---+|5.7.24-log|+---+1rowinsetTime:0.066s 回到顶部 主要用法 { EXPLAIN | DESCRIBE } [EXTENDED | PARTITIONS | FORMAT=[TRADITIONAL | JSON]]SQL_STATEMENT; EXPLAIN和DESCRIBE(可以简写成DESC)都可以用来...
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...
32 Using index for skip scan 表示使用了Skip Scan。详见Skip Scan Range Access Method 33 Using join buffer (Block Nested Loop), Using join buffer (Batched Key Access) 使用Block Nested Loop或Batched Key Access算法提高join的性能。详见https://www.cnblogs.com/chenpingzhao/p/6720531.html ...
UNCACHEABLE SUBQUERY A subquery for which the result cannot be cached and must be re-evaluated for each row of the outer query UNCACHEABLE UNION The second or later select in a UNION that belongs to an uncacheable subquery (see UNCACHEABLE SUBQUERY) SIMPLE 查询语句中不包含UNION或者子查询的...
FOR i IN (SELECT other_xml FROM gv$sql_plan WHERE sql_id = TRIM('&&sql_id.') AND plan_hash_value = TO_NUMBER(TRIM('&&plan_hash_value.')) AND other_xml IS NOT NULL ORDER BY child_number, id) LOOP :other_xml := i.other_xml; ...
1.11.6 Using join buffer (Block Nested Loop) 在连接查询执行过程中,当被驱动表不能有效的利用索引加快访问速度,MySQL一般会为其分配一块名叫join buffer的内存块来加快查询速度,也就是我们所讲的基于块的嵌套循环算法,比如下边这个查询语句: mysql> EXPLAIN SELECT * FROM s1 INNER JOIN s2 ON s1.common_fi...