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
2、执行查询explain select * from a join b on a_id=b_id where b_id in (select c_id from c); mysql> explain select * from a join b on a_id=b_id where b_id in (select c_id from c); EXPLAINSELECT*FROMaJOINbONa_id=b_idWHEREb_idIN(SELECTc_idFROMc); id select_typetablepa...
类似于两表连接中被驱动表的eq_ref访问方法,unique_subquery是针对在一些包含IN子查询的查询语句中,如果查询优化器决定将IN子查询转换为EXISTS子查询,而且子查询可以使用到主键进行等值匹配的话,那么该子查询执行计划的type列的值就是unique_subquery,比如下面的这个查询语句: mysql> EXPLAIN SELECT * FROM s1 WHERE ...
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...
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: ...
EXPLAINSELECT*FROMsc_tableWHEREkey_1IN(SELECTkey_1FROMsc_table_1); 如上,查询语句中有一个子查询,但执行计划中两个表的id都是1,说明查询优化器将子查询转换成连接查询。 二、 带UNION子句的查询,每个SELECT关键字同样会对应一个id,但是还有一点不通的特征,如下: ...
How to explain the code below in the loop so I... Learn more about for loop, csv, faq, process a sequence of files
I did't know that "i" was already defined since my professor usually uses it in examples not pertaining to imaginary numbers. I also took your advice on the file name. Oh, I'm making a loop for forwards euler, since our professor doesn't want us to use ode...
Range checked for each Record(index map: N) 没有找到理想的索引,因此对于从前面表中来的每一个行组合,MYSQL检查使用哪个索引,并用它来从表中返回行。这是使用索引的最慢的连接之一 FirstMatch(tbl_name) 5.6.x开始引入的优化子查询的新特性之一,常见于where字句含有in()类型的子查询。如果内表的数据量比较...
* even though we didn't ask for it here. Be careful not to print any * instrumentation results the user didn't ask for. But we do the * InstrEndLoop call anyway, if possible, to reduce the number of cases * auto_explain has to contend with. */ if (planstate->instrument) InstrEn...