chapter05 实践习题1
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C H A P T E R
5
Advanced SQL
Practice Exercises
5.1 Describe the circumstances in which you would choose to use embed-
ded SQL rather than SQL alone or only a general-purpose programming
language.
Answer: Writing queries in SQL is typically much easier than coding
the same queries in a general-purpose programming language. However
not all kinds of queries can be written in SQL. Also nondeclarative actions
such as printing a report, interacting with a user, or sending the results
of a query to a graphical user interface cannot be done from within SQL.
Under circumstances in which we want the best of both worlds, we can
choose embedded SQL or dynamic SQL, rather than using SQL alone or
using only a general-purpose programming language.
Embedded SQL has the advantage of programs being less complicated
since it avoids the clutter of the ODBC or JDBC function calls, but requires
a specialized preprocessor.
5.2 Write a Java function using JDBC metadata features that takes a Result-
Set as an input parameter, and prints out the result in tabular form, with
appropriate names as column headings.
Answer:
public class ResultSetTable implements TabelModel {
ResultSet result;
ResultSetMetaData metadata;
int num
cols;
ResultSetTable(ResultSet result) throws SQLException {
this.result = result;
metadata = result.getMetaData();
num
cols = metadata.getColumnCount();
for(int i = 1; i <= num cols; i++) {
System.out.print(metadata.getColumnName(i) + ‘‘ ‘‘);
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