查询单个表的数据

在 Java 中，为了存储作者的基本信息，你可以声明一个 Author 类。应根据数据库中的 Data types 和 Value range 选择合适的 Java 数据类型。例如：

• 使用 Int 类型变量存储 int 类型数据。
• 使用 Long 类型变量存储 bigint 类型数据。
• 使用 Short 类型变量存储 tinyint 类型数据。
• 使用 String 类型变量存储 varchar 类型数据。

public class Author {
    private Long id;
    private String name;
    private Short gender;
    private Short birthYear;
    private Short deathYear;

    public Author() {}

     // 省略 getter 和 setter 方法。
}

public class AuthorDAO {

    // 省略实例变量的初始化。

    public List<Author> getAuthors() throws SQLException {
        List<Author> authors = new ArrayList<>();

        try (Connection conn = ds.getConnection()) {
            Statement stmt = conn.createStatement();
            ResultSet rs = stmt.executeQuery("SELECT id, name FROM authors");
            while (rs.next()) {
                Author author = new Author();
                author.setId(rs.getLong("id"));
                author.setName(rs.getString("name"));
                authors.add(author);
            }
        }
        return authors;
    }
}

• 在 使用 JDBC 驱动连接到 TiDB 后，可以通过 conn.createStatement() 创建 Statement 对象。

• 然后调用 stmt.executeQuery("query_sql") 来发起对 TiDB 的数据库查询请求。
• 查询结果存储在 ResultSet 对象中。通过遍历 ResultSet，可以将返回的结果映射到 Author 对象中。

在 Java 中，你可以用相同的 SQL 来处理带有动态参数的数据查询请求。

这可以通过将参数拼接到 SQL 语句中实现，但这种方式存在潜在的 SQL 注入 风险，影响应用的安全性。

为避免此类风险，应使用 Prepared statement 代替普通的 Statement。

public List<Author> getAuthorsByBirthYear(Short birthYear) throws SQLException {
    List<Author> authors = new ArrayList<>();
    try (Connection conn = ds.getConnection()) {
        PreparedStatement stmt = conn.prepareStatement("""
        SELECT * FROM authors WHERE birth_year = ?;
        """);
        stmt.setShort(1, birthYear);
        ResultSet rs = stmt.executeQuery();
        while (rs.next()) {
            Author author = new Author();
            author.setId(rs.getLong("id"));
            author.setName(rs.getString("name"));
            authors.add(author);
        }
    }
    return authors;
}

public List<Author> getAuthorsSortByBirthYear() throws SQLException {
    List<Author> authors = new ArrayList<>();
    try (Connection conn = ds.getConnection()) {
        Statement stmt = conn.createStatement();
        ResultSet rs = stmt.executeQuery("""
            SELECT id, name, birth_year
            FROM authors
            ORDER BY birth_year DESC;
            """);

        while (rs.next()) {
            Author author = new Author();
            author.setId(rs.getLong("id"));
            author.setName(rs.getString("name"));
            author.setBirthYear(rs.getShort("birth_year"));
            authors.add(author);
        }
    }
    return authors;
}

public List<Author> getAuthorsWithLimit(Integer limit) throws SQLException {
    List<Author> authors = new ArrayList<>();
    try (Connection conn = ds.getConnection()) {
        PreparedStatement stmt = conn.prepareStatement("""
            SELECT id, name, birth_year
            FROM authors
            ORDER BY birth_year DESC
            LIMIT ?;
            """);
        stmt.setInt(1, limit);
        ResultSet rs = stmt.executeQuery();
        while (rs.next()) {
            Author author = new Author();
            author.setId(rs.getLong("id"));
            author.setName(rs.getString("name"));
            author.setBirthYear(rs.getShort("birth_year"));
            authors.add(author);
        }
    }
    return authors;
}

public class AuthorCount {
    private Short birthYear;
    private Integer authorCount;

    public AuthorCount() {}

     // 省略 getter 和 setter 方法。
}

public List<AuthorCount> getAuthorCountsByBirthYear() throws SQLException {
    List<AuthorCount> authorCounts = new ArrayList<>();
    try (Connection conn = ds.getConnection()) {
        Statement stmt = conn.createStatement();
        ResultSet rs = stmt.executeQuery("""
            SELECT birth_year, COUNT(DISTINCT id) AS author_count
            FROM authors
            GROUP BY birth_year
            ORDER BY author_count DESC;
            """);

        while (rs.next()) {
            AuthorCount authorCount = new AuthorCount();
            authorCount.setBirthYear(rs.getShort("birth_year"));
            authorCount.setAuthorCount(rs.getInt("author_count"));
            authorCounts.add(authorCount);
        }
    }
    return authorCounts;
}