databaseChangeLog:  
  - changeSet:  
      id: 1  
      author: dev  
      changes:  
        - createTable:  
            tableName: users  
            columns:  
              - column:  
                  name: id  
                  type: BIGINT  
                  autoIncrement: true  
                  constraints:  
                    primaryKey: true  
                    nullable: false  
              - column:  
                  name: username  
                  type: VARCHAR(50)  
                  constraints:  
                    unique: true  

- changeSet:  
    id: 2  
    author: dev  
    changes:  
      - addColumn:  
          tableName: users  
          columns:  
            - column:  
                name: email  
                type: VARCHAR(100)  
                constraints:  
                  nullable: false  

- changeSet:  
    id: 3  
    author: dev  
    changes:  
      - alterTable:  
          tableName: users  
          columns:  
            - column:  
                name: username  
                type: VARCHAR(100)  # Увеличение длины  
      - renameColumn:  
          tableName: users  
          oldColumnName: email  
          newColumnName: email_address  

- changeSet:  
    id: 4  
    author: dev  
    runAlways: true  
    changes:  
      - sql:  
          sql: "INSERT INTO logs (message) VALUES ('Migration executed')"  
runOnChange="true" – выполняется только если содержимое changeSet’а изменилось.

- changeSet:  
    id: 5  
    author: dev  
    preConditions:  
      - tableExists:  
          tableName: users  
    changes:  
      - addColumn:  
          tableName: users  
          columns:  
            - column:  
                name: status  
                type: VARCHAR(20)  

databaseChangeLog:  
  - include:  
      file: db/changelog/v1.0/001-create-tables.yaml  
  - include:  
      file: db/changelog/v1.0/002-add-constraints.yaml  

- changeSet:  
    id: 6  
    author: dev  
    context: "!prod"  # Не выполнять в production  
    changes:  
      - insert:  
          tableName: test_data  
          columns:  
            - column:  
                name: value  
                value: "Test"  

--liquibase formatted sql  

--changeset dev:7  
CREATE INDEX idx_user_email ON users(email);  

--changeset dev:8 context:prod  
ALTER TABLE users ADD COLUMN last_login TIMESTAMP;  

public class Task020625 {
    public static void main(String[] args) {
        String s1 = new String("Java");
        String s2 = "Java";
        String s3 = s1.intern();
        
        System.out.println((s1 == s2) + " " + (s2 == s3));
    }
}

int x = true; // Ошибка компиляции
if (1) { ... } // Тоже ошибка

Boolean obj = true;     // упаковка
boolean val = obj;      // распаковка
Также есть кэширование значений: Boolean.TRUE и Boolean.FALSE — это единственные экземпляры класса Boolean, которые обычно и используются.

public class Task030625 {
    public static void main(String[] args) {
        boolean a = false;
        boolean b = true;
        boolean c = a != b == !b;
        System.out.println(c);
    }
}

- changeSet:
    id: 1
    author: dev
    changes:
      - createTable:
          tableName: users
          columns:
            - column:
                name: id
                type: INT
                constraints:
                  primaryKey: true
      - rollback:
          dropTable:
            tableName: users

- changeSet:
    id: 2
    author: dev
    changes:
      - sql:
          sql: "ALTER TABLE users ADD COLUMN last_login TIMESTAMP"
      - rollback:
          sql:
            sql: "ALTER TABLE users DROP COLUMN last_login"

liquibase tag v1.0
или через changelog:

yaml
- changeSet:
    id: 3
    author: dev
    changes:
      - tagDatabase:
          tag: v1.0

liquibase rollback v1.0

- changeSet:
    id: 4
    author: dev
    changes:
      - tagDatabase:
          tag: v1.1

liquibase rollbackCount 1

liquibase rollback v1.0

liquibase rollbackToDate 2024-03-15

liquibase rollbackCount 3  # Откатит 3 последних изменения

databaseChangeLog:
  - changeSet:
      id: 1
      author: dev
      changes:
        - createTable:
            tableName: users
            columns:
              - column:
                  name: id
                  type: INT
                  constraints:
                    primaryKey: true
        - rollback:
            dropTable:
              tableName: users

  - changeSet:
      id: 2
      author: dev
      changes:
        - addColumn:
            tableName: users
            column:
              name: username
              type: VARCHAR(50)
        - rollback:
            dropColumn:
              tableName: users
              columnName: username

  - changeSet:
      id: 3
      author: dev
      changes:
        - tagDatabase:
            tag: v1.0

liquibase update

liquibase rollback v1.0

public class Task040525 {
    public static void main(String[] args) {
        System.out.println('A' + 1.5F + "Java");
    }
}