InnoDB引擎 count( * )时 rows = 2(全表只有2行数据),需要扫描全表,Extra里面的内容是 "Using index",说明该 count( *)操作使用了索引。 MyISAM引擎 count( * )时 rows = NULL,Extra里面的内容是 "Select tables optimized away",它包含的意思是:MyISAM 表以单独的行数存储总数,执行 count查询时,MySQL...
mysql> explain format=tree select count(*) from lineitem\G *** 1. row *** EXPLAIN -> Count rows in lineitem 2.1.2 COUNT并行在InnoDB 存储引擎的实现 (1) SQL引擎调用handler API 接口“::ha_records”,传递优化器选择的索引给InnoDB存储引擎,获取COUNT结果。 (2) InnoDB存储引擎只支持主键...
a row count was typically performed by traversing a smaller secondary index and invoking a handler call for each record. A single handler call to the storage engine to count rows in the clustered index
mysql TABLE_ROWS 和 count 不相等 解决办法 mysql_num_rows作用,索引的作用就是快速找出在一个列上用一特定值的行。如果没有索引,MySQL不得不首先以第一条记录开始并然后读完整个表直到它找出相关的行。索引的类型:先写一个建表语句:CREATETABLE`t_order`( `id`in
mysql> SELECT FOUND_ROWS() 表示的是: 在上一查询之后,你只需要用FOUND_ROWS()就能获得查询总数,这个数目是抛掉了LIMIT之后的结果数 其中第一个sql里面的SQL_CALC_FOUND_ROWS不可省略,它表示需要取得结果数,也是后面使用FOUND_ROWS()函数的铺垫。 第二个SELECT将返回第一条SELECT如果没有LIMIT时返回的行数, ...
1. found_rows() found_rows()用于查询同一连接下,上一条执行select查询返回的行数,包括show 语句返回的行数。中间可以插入执行dml语句,返回依然是上一条select语句返回的行数。 mysql>select*fromt6;+---+---+---+ | id | k1 | k2 | +---+--...
ndb_select_countprints the number of rows in one or moreNDBtables. With a single table, the result is equivalent to that obtained by using the MySQL statementSELECT COUNT(*) FROMtbl_name. Usage ndb_select_count[-cconnection_string]-ddb_nametbl_name[,tbl_name2[,...]] ...
ndb_select_count prints the number of rows in one or more NDB tables. With a single table, the result is equivalent to that obtained by using the MySQL statement SELECT COUNT(*) FROM tbl_name. Usagendb_select_count [-c connection_string] -ddb_name tbl_name[, tbl_name2[, ...]] ...
count rows in a partitionPosted by: Darren White Date: May 14, 2013 10:46PM I have innodb and version 5.6 I have some tables partitioned by month like this: ALTER TABLE pgs.log_01 PARTITION BY LIST ( month( time ) ) ( PARTITION p0 VALUES IN ( 0 ), PARTITION p1 VALUES...
mysql> create index idx_rowguid on api_runtime_log(rowguid);Query OK, 0 rows affected (0.01 sec)Records: 0 Duplicates: 0 Warnings: 0mysql> select count(*) from api_runtime_log;+---+| count(*) |+---+| 5718952 |+---+1 row in set (0.89 sec)mysql> explain select count...