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. ...
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 ...
| 1 | SIMPLE | s2 | NULL | ALL | NULL | NULL | NULL | NULL | 9954 | 100.00 | Using join buffer (Block Nested Loop) | +---+---+---+---+---+---+---+---+---+---+---+---+ 2 rows in set, 1 warning (0.01 sec) 可以看到这个连接查询的执行计划中有两条记录,这...
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...
1 row in set, 1 warning (0.00 sec) 二、结果列详细说明: 2.1、id 列 用下面的例子来说明,在多张表的查询中,突出的更显著。 1、建表: create table a(a_id int); create table b(b_id int); create table c(c_id int); 2、执行查询explain select * from a join b on a_id=b_id where...
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)....
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...
* 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...
execution info 信息除了基本的 time 和loop 信息外,还包含算子特有的执行信息,主要包含了该算子发送 RPC 请求的耗时信息以及其他步骤的耗时。 Point_Get Point_Get 算子可能包含以下执行信息: Get:{num_rpc:1, total_time:697.051µs}:向 TiKV 发送 Get 类型的 RPC 请求的数量 (num_rpc) 和所有 RPC 请...
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...