Query Data from a Single Table

In Java, to store the basic information of authors, you can declare a class Author. You should choose appropriate Java data types according to the Data types and Value range in the database. For example:

• Use a variable of type Int to store data of type int.
• Use a variable of type Long to store data of type bigint.
• Use a variable of type Short to store data of type tinyint.
• Use a variable of type String to store data of type varchar.

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

    public Author() {}

     // Skip the getters and setters.
}

public class AuthorDAO {

    // Omit initialization of instance variables.

    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;
    }
}

• After connecting to TiDB using the JDBC driver, you can create a Statement object with conn.createStatus().

• Then call stmt.executeQuery("query_sql") to initiate a database query request to TiDB.
• The query results are stored in a ResultSet object. By traversing ResultSet, the returned results can be mapped to the Author object.

In Java, you can use the same SQL to handle data query requests with dynamic parameters.

This can be done by concatenating parameters into a SQL statement. However, this method poses a potential SQL Injection risk to the security of the application.

To deal with such queries, use a Prepared statement instead of a normal 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() {}

     // Skip the getters and setters.
}

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 authorCount;
}