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...
valueIN(SELECTkey_columnFROMsingle_tableWHEREsome_expr) 10 range:范围扫描,表示检索了指定范围的行,主要用于有限制的索引扫描。比较常见的范围扫描是带有BETWEEN子句或WHERE子句里有>、>=、<、<=、IS NULL、<=>、BETWEEN、LIKE、IN()等操作符。 SELECT*FROMtbl_nameWHEREkey_columnBETWEEN10and20;SELECT*FROMtbl...
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,如果是子查询,id的序号会递增,id值越大优先级越高,越先被执行 代码语言:javascript 代码运行次数:0 mysql>explain select*from emp e where e.deptnoin(select d.deptno from dept d where d.dname='SALEDept'...
-- name字段有索引explainSELECTnameFROMt1groupbyname 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...
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 cnblogs.com/chenpingzha Using MRR使用了Multi-Range Read优化策略。详见 ...
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...
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 Using MRR 使...
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...
What would happen to the time complexity (Big-O) of the methods in an array implementation of a stack if the top of the stack were at position 0? Explain. Explain array in java. Explain the difference between while loop and for loop? Give an example for the while loop and the for lo...
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javascript:void(0) ...