MyBatis-Flex is an elegant Mybatis Enhancement Framework.

@Table("tb_account")
public class Account {

    @Id(keyType = KeyType.Auto)
    private Long id;
    private String userName;
    private Date birthday;
    private int sex;

    //getter setter
}

public interface AccountMapper extends BaseMapper<Account> {
    //only Mapper interface define.
}

class HelloWorld {
    public static void main(String... args) {

        HikariDataSource dataSource = new HikariDataSource();
        dataSource.setJdbcUrl("jdbc:mysql://127.0.0.1:3306/mybatis-flex");
        dataSource.setUsername("username");
        dataSource.setPassword("password");

        MybatisFlexBootstrap.getInstance()
                .setDataSource(dataSource)
                .addMapper(AccountMapper.class)
                .start();

        AccountMapper mapper = MybatisFlexBootstrap.getInstance()
                .getMapper(AccountMapper.class);


        //id=100
        Account account = mapper.selectOneById(100);
    }
}

//use QueryWrapper to build query conditions
QueryWrapper query = QueryWrapper.create()
        .select()
        .from(ACCOUNT)
        .where(ACCOUNT.ID.ge(100))
        .and(ACCOUNT.USER_NAME.like("zhang").or(ACCOUNT.USER_NAME.like("li")));

// execute SQL：
// SELECT * FROM tb_account
// WHERE tb_account.id >=  100
// AND (tb_account.user_name LIKE '%zhang%' OR tb_account.user_name LIKE '%li%' )
List<Account> accounts = mapper.selectListByQuery(query);

//use QueryWrapper to build query conditions
QueryWrapper query = QueryWrapper.create()
        .select()
        .from(ACCOUNT)
        .where(ACCOUNT.ID.ge(100))
        .and(ACCOUNT.USER_NAME.like("zhang").or(ACCOUNT.USER_NAME.like("li")))
        .orderBy(ACCOUNT.ID.desc());

// execute SQL：
// SELECT * FROM tb_account
// WHERE tb_account.id >=  100
// AND (tb_account.user_name LIKE '%zhang%' OR tb_account.user_name LIKE '%li%' )
// ORDER BY tb_account.id DESC
// LIMIT 40,10
Page<Account> accountPage = mapper.paginate(5, 10, query);

QueryWrapper query=new QueryWrapper();
query.select().from(ACCOUNT)

// SQL:
// SELECT * FROM tb_account

QueryWrapper query=new QueryWrapper();
query.select(ACCOUNT.ID,ACCOUNT.USER_NAME).from(ACCOUNT)

// SQL:
// SELECT tb_account.id, tb_account.user_name
// FROM tb_account

QueryWrapper query = new QueryWrapper()
    .select(ACCOUNT.ID
        , ACCOUNT.USER_NAME
        , ARTICLE.ID.as("articleId")
        , ARTICLE.TITLE)
    .from(ACCOUNT.as("a"), ARTICLE.as("b"))
    .where(ACCOUNT.ID.eq(ARTICLE.ACCOUNT_ID));

// SQL:
// SELECT a.id, a.user_name, b.id AS articleId, b.title
// FROM tb_account AS a, tb_article AS b
// WHERE a.id = b.account_id

 QueryWrapper query=new QueryWrapper()
        .select(
            ACCOUNT.ID,
            ACCOUNT.USER_NAME,
            max(ACCOUNT.BIRTHDAY),
            avg(ACCOUNT.SEX).as("sex_avg")
        ).from(ACCOUNT);

// SQL:
// SELECT tb_account.id, tb_account.user_name,
// MAX(tb_account.birthday),
// AVG(tb_account.sex) AS sex_avg
// FROM tb_account

QueryWrapper queryWrapper=QueryWrapper.create()
    .select()
    .from(ACCOUNT)
    .where(ACCOUNT.ID.ge(100))
    .and(ACCOUNT.USER_NAME.like("michael"));

// SQL:
// SELECT * FROM tb_account
// WHERE tb_account.id >=  ?
// AND tb_account.user_name LIKE  ?

QueryWrapper queryWrapper=QueryWrapper.create()
    .select()
    .from(ACCOUNT)
    .where(ACCOUNT.ID.ge(100))
    .and(
        exists(
            selectOne().from(ARTICLE).where(ARTICLE.ID.ge(100))
        )
    );

// SQL:
// SELECT * FROM tb_account
// WHERE tb_account.id >=  ?
// AND EXIST (
//  SELECT 1 FROM tb_article WHERE tb_article.id >=  ?
// )

QueryWrapper queryWrapper=QueryWrapper.create()
    .select()
    .from(ACCOUNT)
    .where(ACCOUNT.ID.ge(100))
    .and(ACCOUNT.SEX.eq(1).or(ACCOUNT.SEX.eq(2)))
    .or(ACCOUNT.AGE.in(18,19,20).or(ACCOUNT.USER_NAME.like("michael")));

// SQL:
// SELECT * FROM tb_account
// WHERE tb_account.id >=  ?
// AND (tb_account.sex =  ?  OR tb_account.sex =  ? )
// OR (tb_account.age IN (?,?,?) OR tb_account.user_name LIKE  ? )

QueryWrapper queryWrapper=QueryWrapper.create()
    .select()
    .from(ACCOUNT)
    .groupBy(ACCOUNT.USER_NAME);

// SQL:
// SELECT * FROM tb_account
// GROUP BY tb_account.user_name

QueryWrapper queryWrapper=QueryWrapper.create()
    .select()
    .from(ACCOUNT)
    .groupBy(ACCOUNT.USER_NAME)
    .having(ACCOUNT.AGE.between(18,25));

// SQL:
// SELECT * FROM tb_account
// GROUP BY tb_account.user_name
// HAVING tb_account.age BETWEEN  ? AND ?

QueryWrapper queryWrapper=QueryWrapper.create()
        .select()
        .from(ACCOUNT)
        .orderBy(ACCOUNT.AGE.asc(), ACCOUNT.USER_NAME.desc().nullsLast());

// SQL:
// SELECT * FROM tb_account
// ORDER BY age ASC, user_name DESC NULLS LAST

QueryWrapper queryWrapper = QueryWrapper.create()
    .select()
    .from(ACCOUNT)
    .leftJoin(ARTICLE).on(ACCOUNT.ID.eq(ARTICLE.ACCOUNT_ID))
    .where(ACCOUNT.AGE.ge(10));

// SQL:
// SELECT * FROM tb_account
// LEFT JOIN tb_article
// ON tb_account.id = tb_article.account_id
// WHERE tb_account.age >=  ?

QueryWrapper queryWrapper = QueryWrapper.create()
    .select()
    .from(ACCOUNT)
    .orderBy(ACCOUNT.ID.desc())
    .limit(10)
    .offset(20);

// MySql:
// SELECT * FROM `tb_account` ORDER BY `id` DESC LIMIT 20, 10

// PostgreSQL:
// SELECT * FROM "tb_account" ORDER BY "id" DESC LIMIT 20 OFFSET 10

// Informix:
// SELECT SKIP 20 FIRST 10 * FROM "tb_account" ORDER BY "id" DESC

// Oracle:
// SELECT * FROM (SELECT TEMP_DATAS.*,
//  ROWNUM RN FROM (
//          SELECT * FROM "tb_account" ORDER BY "id" DESC)
//      TEMP_DATAS WHERE  ROWNUM <=30)
//  WHERE RN >20

// Db2:
// SELECT * FROM "tb_account" ORDER BY "id" DESC
// OFFSET 20 ROWS FETCH NEXT 10 ROWS ONLY

// Sybase:
// SELECT TOP 10 START AT 21 * FROM "tb_account" ORDER BY "id" DESC

// Firebird:
// SELECT * FROM "tb_account" ORDER BY "id" DESC ROWS 20 TO 30