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. ...
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...
In python, the range() function essentially is used with the for loop, it returns a sequence of numbers that begin and end as per the limits specified within the function. For eg: The code snippet below, runs a for loop ranging from lower limit = 0 to upper limit = 10 (exclusive)....
If you want to make your queries as fast as possible, look out for Extra column values of Using filesort and Using temporary, or, in JSON-formatted EXPLAINoutput, for using_filesort and using_temporary_table properties equal to true. 大概的意思就是说,如果你想要优化你的查询,那就要注意extra...
1 row in set, 1 warning (0.01 sec) 然后这输出的一大坨东西就是所谓的执行计划,我的任务就是带领大家看懂这一大坨东西里边的每个列都是干什么用的,以及在这个执行计划的辅助下,我们应该怎样改进自己的查询语句以使查询执行起来更高效。 其实除了以SELECT开头的查询语句,其余的DELETE、INSERT、REPLACE以及UPDATE语句...
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: ...
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...
How to explain the code below in the loop so I... Learn more about for loop, csv, faq, process a sequence of files
* 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...
int a,b,c; In this statement,comma is a separator and tells to the compiler that these (a, b, and c) are three different variables. 2) Comma (,) as an operator Sometimes we assign multiple values to a variable using comma, in that case comma is known as operator. ...