relational join meaning in English

关系合并

Too many complex relational joins between too many tables can hinder performance
太多表间的关系联接太多、太复杂可能会影响性能。
When user defined functions ( udfs ) are involved in the join predicate , the algorithms for the computation of relational joins can not be used directly . in the paper , the restricting transformation function r , is defined , which can restrict some variable ' s values . without scanning the entire relation , performance of join algorithm can be improved greatly
当连接条件中包含用户自定义的复杂函数时，原有的连接算法不能直接应用于该连接运算，为此，本文提出了限定变换函数t _ r概念，来限定连接谓词中某些变元的取值范围，从而避免对整个关系的扫描，达到提高连接算法性能的目的。