What is a difference between traditional loop and for-each loop? I wonder if there is a difference between these: 1-) 2-) If there is not any difference which one is more common or efficient? Traditional loop allows to modify the list, e.g.: you can add extra eleme... ...
What is a difference between traditional loop and for-each loop? I wonder if there is a difference between these: 1-) 2-) If there is not any difference which one is more common or efficient? Traditional loop allows to modify the list, e.g.: you can add extra eleme... ...
MySQL explains how it would process the statement, including information about how tables are joined and in which order. For information about using EXPLAIN to obtain execution plan information, see Section 8.8.2, “EXPLAIN Output Format”. 当...
) ENGINE=InnoDBDEFAULTCHARSET=utf81rowinsetTime:0.012s 回到顶部 输出说明 mysql root@localhost:employees>explainselectcount(*)fromemployees;+---+---+---+---+---+---+---+---+---+---+---+---+|id|select_type|table|partitions|type|possible_keys|key|key_len|ref|rows|filtered|Extra...
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 ...
(Block Nested Loop)||1|SIMPLE|sg|NULL|ALL|NULL|NULL|NULL|NULL|1|100.00|Using where;Using joinbuffer(Block Nested Loop)|+---+---+---+---+---+---+---+---+---+---+---+---+ 这个查询,用explain执行一下,id序号都是1,那么MySQL的执行顺序就是从上到下执行的。 如果id不同,如果...
8 unique_subquery:该类型和eq_ref类似,但是使用了IN查询,且子查询是主键或者唯一索引。例如: value IN (SELECT primary_key FROM single_table WHERE some_expr) 9 index_subquery:和unique_subquery类似,只是子查询使用的是非唯一索引 value IN (SELECT key_column FROM single_table WHERE some_expr) ...
where 'i' is the loop variable 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 effic...
Using index for skip scan 表示使用了Skip Scan。详见Skip Scan Range Access Method 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 ...
DEPENDENT UNION Second or later SELECT statement in a UNION, dependent on outer query DERIVED Derived table MATERIALIZED Materialized subquery 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...