使用了连接缓存:Block Nested Loop,连接算法是块嵌套循环连接;Batched Key Access,连接算法是批量索引连接 Impossible where 该WHERE子句始终为false,不能选择任何行。 Select tables optimized away 在没有GROUP BY子句的情况下,基于索引优化MIN/MAX操作,或者对于MyISAM存储引擎优化COUNT(*)操作,不必等到执行阶段再进行...
EXPLAIN returnsa row of information for each table used in the SELECT statement. It lists thetables in the output in the order that MySQL would read them while processingthe statement. MySQL resolves all joins using a nested-loop join method. Thismeans that MySQL reads a row from the first ...
Accessing row source 2 is known a probing the inner table For nested loops to be efficient it is important that the first row source returns as few rows as possible as this directly controls the number of probes of the second row source. Also it helps if the access method for row source...
EXPLAIN returnsa row of information for each table used in the SELECT statement. It lists thetables in the output in the order that MySQL would read them while processingthe statement. MySQL resolves all joins using a nested-loop join method. Thismeans that MySQL reads a row from the first...
If this returns a lot of rows then this can have a negative affect on all subsequent operations Probed Table - This is the object we look-up data in after we have retrieved relevant key data from the driving table. How does Oracle access data?
We discovered that the Hes1 protein exhibits a large oscillatory pattern averaging a circadian-like periodicity (≈25 h), while an oscillatory pattern with a shorter periodicity (≈4 h) was found when this larger oscillatory trend was removed. These nested ultradian (shorter than one day but ...