摘要：有些计算器，只能进行单步计算，就是说只能输入数字和加减乘除四则运算符号，而不能有括号的出现。可编程计算器就是指能输入括号、数字和四则运算符号，并对所输入的四则运算表达式进行分析，得最终计算出结果的计... 阅读全文

摘要：l The relationalalgebra is procedural(过程化) query language Aset of operations, take one or two limited rela... 阅读全文

摘要：事务：A transaction is asequence of queries and update statements on DB, executed as a single, and arestarted... 阅读全文