This optimization improves the efficiency of direct comparisons between a nonindexed column and a constant. In such cases, the condition is “pushed down” to the storage engine for evaluation. This optimization can be used only by the NDB storage engine.
这种优化提高了非索引列和常量之间直接比较的效率。 在这种情况下，条件将“推入”存储引擎进行评估。 此优化只能由NDB存储引擎使用。
For NDB Cluster, this optimization can eliminate the need to send nonmatching rows over the network between the cluster's data nodes and the MySQL server that issued the query, and can speed up queries where it is used by a factor of 5 to 10 times over cases where condition pushdown could be but is not used.
对于NDB群集，此优化可以消除在群集的数据节点与发出查询的MySQL服务器之间通过网络发送不匹配的行的需求，并且可以将查询的使用速度提高5到10倍（在某些情况下） 可以但不使用条件下推的地方。
Suppose that an NDB Cluster table is defined as follows:
https://dev.mysql.com/doc/refman/5.7/en/engine-condition-pushdown-optimization.html
