The SELECT identifier. This is the sequential number of the SELECT within the query. The value can be NULL if the row refers to the union result of other rows. In this case, the table column shows a value like <
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...
问答精选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......
PHP foreach loop array I have a script where it's displaying user info on a leader board. It's grabbing each user's display info through the 'registrations' table as shown in the top sql, however their back-end info (userna... ...
| 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...
---1SIMPLE a (NULL)ALL(NULL) (NULL) (NULL) (NULL)1100.00(NULL)1SIMPLE b (NULL)ALL(NULL) (NULL) (NULL) (NULL)1100.00Usingwhere; Usingjoinbuffer (Block Nested Loop)1SIMPLE c (NULL)ALL(NULL) (NULL) (NULL) (NULL)1100.00Usingwhere; FirstMatch(b); Usingjoinbuffer (Block Nested Loop)...
---1SIMPLE a (NULL)ALL(NULL) (NULL) (NULL) (NULL)1100.00(NULL)1SIMPLE b (NULL)ALL(NULL) (NULL) (NULL) (NULL)1100.00Usingwhere; Usingjoinbuffer (Block Nested Loop)1SIMPLE c (NULL)ALL(NULL) (NULL) (NULL) (NULL)1100.00Usingwhere; FirstMatch(b); Usingjoinbuffer (Block Nested Loop)...
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. ...
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: ...
EXPLAIN 语句提供有关MySQL执行语句的信息,每个表返回一行信息。处理语句时,读取它们的顺序列出输出中的表 执行EXPLAIN 语句会打印出下列内容 id, select_type, table, partitions, type, possible_keys, key , key_len, ref, rows, filtered, Extra