Integrity constraints ensure that changes made to the database by authorized users do not result in a loss of data consistency. Thus, integrity constraints guard against accidental damage to the database. Examples of integrity constraints are:
In this series, we continue our study of SQL. We consider more complex forms of SQL queries, view definition, transactions, integrity constrains, more details regarding SQL data definition, and authorization. 继续阅读“Relational Databases ~ Intermediate SQL I”
Of the data types that support insert and delete for collections of objects, the most important is called the pushdown stack. 继续阅读“Abstract Data Types～Stack ADT”
DEVELOPING ABSTRACT MODELS for our data and for the ways in which our programs process those data is an essential ingredient in the process of solving problems with a computer. In this series, we consider abstract data types (ADTs), which allow us to build programs that use high-level abstractions. With abstract data types, we can separate the conceptual transformations that our programs perform on our data from any particular data-structure representation and algorithm implementation. 继续阅读“Abstract Data Types～Abstract Objects and Collections of Objects”
Arrays, linked lists, and strings all provide simple ways to structure data sequentially. They provide a first level of abstraction that we can use to group objects in ways amenable to processing the objects efficiently. Having settled on these abstractions, we can use them in a hierarchical fashion to build up more complex structures. We can contemplate arrays of arrays, arrays of lists, arrays of strings, and so forth. 继续阅读“Elementary Data Structures ~ Compound Data Structures”
We use the term string to refer to a variable-length array of characters, defined by a starting point and by a string-termination character marking the end. Strings are valuable as low-level data structures, for two basic reasons. 继续阅读“Elementary Data Structures ~ Strings”
串扰是发生在一个信号与返回路径和另外一个信号与返回路径之间的效应，是不同传输线之间的能量耦合。当不同结构的电磁场相互作用时，就会产生串扰。不只是在信号路径上，返回路径也会产生串扰。 继续阅读“信号完整性小记 ~ 串扰”
SQL provides a mechanism for nesting subqueries. A subquery is a select-from-where expression that is nested within another query. 继续阅读“Relational Databases ~ Introduction to SQL IV”
The SQL operations union, intersect, and except operate on relations and correspond to the mathematical set-theory operations ∪, ∩, —. We shall now construct queries involving the union, intersect, and except operations over two sets. 继续阅读“Relational Databases ~ Introduction to SQL III”
