User: what should i remember in sql 12g ch1-5 and 8
Assistant: In Oracle SQL 12c, Chapters 1-5 and 8 likely cover the foundational aspects of SQL and database management. Here's a general overview of what you might need to remember from these chapters:

### Chapter 1: Introduction to Oracle SQL
- **Basic SQL Concepts**: Understand the purpose and history of SQL, its standards, and how it interacts with relational databases.
- **SQL Environment**: Get familiar with SQL Developer and SQL*Plus, the primary tools for interacting with Oracle databases.
- **Data Definition Language (DDL)**: Learn how to create and manage database schemas using commands like `CREATE`, `ALTER`, and `DROP`.

### Chapter 2: Retrieving Data Using the SQL SELECT Statement
- **Basic SELECT Statements**: Understand how to query data using the `SELECT` statement.
- **Filtering and Sorting Data**: Use `WHERE` clauses for filtering rows and `ORDER BY` for sorting.
- **Built-in Functions**: Familiarize with scalar and aggregate functions like `SUM`, `AVG`, `MAX`, `MIN`, and `COUNT`.

### Chapter 3: Using Single-Row Functions to Customize Output
- **String Functions**: Functions like `CONCAT`, `SUBSTR`, and `INSTR`.
- **Number Functions**: Functions like `ROUND`, `TRUNC`, and arithmetic operations.
- **Date Functions**: `SYSDATE`, `ADD_MONTHS`, and `LAST_DAY`.
- **Conversion Functions**: `TO_CHAR`, `TO_DATE`, `TO_NUMBER`.

### Chapter 4: Reporting Aggregated Data Using the Group Functions
- **Group By Clause**: Using `GROUP BY` to aggregate data.
- **HAVING Clause**: Filtering groups with the `HAVING` clause.
- **Grouping Functions**: Understanding the nuances of using functions like `GROUPING` with complex queries.

### Chapter 5: Displaying Data from Multiple Tables
- **Joins**: Inner, outer, and cross joins; understanding `LEFT JOIN`, `RIGHT JOIN`, and `FULL OUTER JOIN`.
- **Self-Joins and Set Operations**: Concepts like self-joins, `UNION`, `INTERSECT`, and `MINUS`.

### Chapter 8: Using Subqueries to Solve Queries
- **Subquery Basics**: Understand simple, correlated, and nested subqueries.
- **Single-row vs. Multi-row Subqueries**: How to handle scenarios where subqueries return one versus multiple rows or columns.
- **WHERE and FROM Clauses**: How subqueries can be used within these clauses to extend query capabilities.

Each chapter builds on the concepts of constructing and managing database queries, allowing you to efficiently extract, manipulate, and organize data. To excel in these areas, practice writing queries using different constructs and understand how they work together in various scenarios
User: 1.	Create a table named WORKER to include the columns listed in the following sample table. WORKER_ID is the Primary Key. Default value for CITY is Toronto. 
Assistant: To create a table named `WORKER` with specific requirements such as a primary key and a default value for a column in Oracle SQL 12c, you can use the following SQL statement:

```sql
CREATE TABLE WORKER (
    WORKER_ID INT PRIMARY KEY, -- Primary key constraint
    FIRST_NAME VARCHAR2(50),   -- Assuming a max length of 50 for first name
    LAST_NAME VARCHAR2(50),    -- Assuming a max length of 50 for last name
    CITY VARCHAR2(50) DEFAULT 'Toronto', -- Default value for CITY
    JOIN_DATE DATE             -- Assuming a date column for join date
);
```

### Key Points:
- `WORKER_ID` is defined as the primary key, which ensures that each worker has a unique identifier.
- `FIRST_NAME` and `LAST_NAME` are defined as `VARCHAR2` with a specified maximum length. Adjust the length as necessary based on your requirements.
- `CITY` is also a `VARCHAR2`, and it has a default value set to 'Toronto'. This means that if a value is not provided for `CITY` during insert, 'Toronto' will be used automatically.
- `JOIN_DATE` is defined as a `DATE` type, suitable for storing dates.

You can adjust the data types and constraints according to your specific data requirements or any additional constraints that you might need.
User: 3.	Add a constraint to make sure the WORKER_ID value entered in the WAGE table is a valid value contained in the Worker table. The constraint is created in a way that associated rows of the WAGE table are deleted automatically if a row in the WORKER table is deleted. Make table modifications as needed so that you can add the required constraint.	
Assistant: To ensure that the `WORKER_ID` in the `WAGE` table is a valid reference to an existing ID in the `WORKER` table, you need to create a foreign key constraint. Furthermore, you will set this constraint so that any time a row in the `WORKER` table is deleted, the corresponding rows in the `WAGE` table are automatically deleted (cascading delete).

First, we'll assume you have a basic `WAGE` table structure, and then I'll show you how to modify it to include the foreign key constraint with cascading behavior.

### Step 1: Create or Modify the `WAGE` Table

If you haven't already created the `WAGE` table, you can do so, including `WORKER_ID` as a column. If the table exists, you can alter it to add a new column if necessary.

```sql
CREATE TABLE WAGE (
    WAGE_ID INT PRIMARY KEY,         -- Primary key for the WAGE table
    WORKER_ID INT,                   -- Foreign key to reference WORKER
    SALARY NUMBER(10, 2),            -- Example salary field
    PAY_PERIOD VARCHAR2(20)          -- Example pay period field
);
```

### Step 2: Add the Foreign Key Constraint with Cascade Delete

Now, apply the foreign key constraint to the `WORKER_ID` field in the `WAGE` table to reference the `WORKER_ID` in the `WORKER` table. Set it up to cascade on delete.

```sql
ALTER TABLE WAGE
ADD CONSTRAINT fk_worker_id
FOREIGN KEY (WORKER_ID)
REFERENCES WORKER(WORKER_ID)
ON DELETE CASCADE;
```

### Explanation

- **Foreign Key `fk_worker_id`:** This constraint ensures that any `WORKER_ID` entered into the `WAGE` table must exist in the `WORKER` table.
- **`ON DELETE CASCADE`:** This clause ensures that when a row in the `WORKER` table is deleted, all corresponding rows in the `WAGE` table with the same `WORKER_ID` will also be automatically deleted.

This setup helps maintain referential integrity between the two tables while managing
User: give name to the constraint
Assistant: Certainly! When adding a constraint, you can explicitly name it to easily reference it later for modifications or for clarity in understanding the schema design. Here's the SQL code including a specific name for the foreign key constraint:

### Step 1: Create or Modify the `WAGE` Table
If the `WAGE` table does not exist, you can create it with the necessary columns as shown below. If it does exist, you can proceed to step 2 to add the constraint.

```sql
CREATE TABLE WAGE (
    WAGE_ID INT PRIMARY KEY,         -- Primary key for the WAGE table
    WORKER_ID INT,                   -- Foreign key to reference WORKER
    SALARY NUMBER(10, 2),            -- Example salary field
    PAY_PERIOD VARCHAR2(20)          -- Example pay period field
);
```

### Step 2: Add the Foreign Key Constraint with Cascade Delete

Add a constraint to the `WAGE` table using a specific name for the foreign key constraint.

```sql
ALTER TABLE WAGE
ADD CONSTRAINT fk_worker_id_wage
FOREIGN KEY (WORKER_ID)
REFERENCES WORKER(WORKER_ID)
ON DELETE CASCADE;
```

### Explanation:

- **Constraint Name `fk_worker_id_wage`:** This is the given name for the foreign key constraint. It can be helpful to follow a naming convention that reflects the relationship between the tables for better clarity, such as using the pattern `fk_<referenced_table>_<referencing_table>` or another consistent approach.
- **`ON DELETE CASCADE`:** Ensures that when a row from the `WORKER` table is deleted, any related rows in the `WAGE` table are also deleted, maintaining referential integrity.

By naming the constraint, you make it easier to manage database schemas, especially if you need to alter or drop the constraint in the future.
User: add constraint with name
Assistant: