Design a sponsor sql schema for an educational app with the following requirements and use best practices:
- Assume the subject table already exists
- Each sponsor has a unique id and a name (can be non-unique)
- Each sponsor can place the same or different ads on different subjects
- Each ad has a banner and/or an interstitial
- Each sponsor has timeslots at which their ad is shown (for each day)
- Each sponsor could buy the each day timeslots for any multiple of months such as 1 month, 3 months, 12 months etc
To design a SQL schema for the educational app based on the provided requirements, we need to create several tables that will effectively capture the relationships between sponsors, ads, subjects, and timeslots. Below is a proposed schema along with explanations for each table and its columns.

### SQL Schema

```sql
-- Table to store Sponsors
CREATE TABLE Sponsors (
    sponsor_id SERIAL PRIMARY KEY,          -- Unique ID for each sponsor
    name VARCHAR(255) NOT NULL              -- Name of the sponsor (can be non-unique)
);

-- Table to store Ads
CREATE TABLE Ads (
    ad_id SERIAL PRIMARY KEY,                -- Unique ID for each ad
    sponsor_id INT NOT NULL,                 -- Foreign key referencing Sponsors
    banner_url VARCHAR(255),                 -- URL for the ad banner (nullable)
    interstitial_url VARCHAR(255),           -- URL for the interstitial ad (nullable)
    created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP, -- Timestamp when ad was created
    FOREIGN KEY (sponsor_id) REFERENCES Sponsors(sponsor_id) ON DELETE CASCADE
);

-- Table to store Subjects (Assumed to already exist)
-- CREATE TABLE Subjects (
--     subject_id SERIAL PRIMARY KEY,
--     subject_name VARCHAR(255) NOT NULL
-- );

-- Table to store Ads shown on Subjects
CREATE TABLE SubjectAds (
    subject_ad_id SERIAL PRIMARY KEY,        -- Unique ID for each subject-ad relationship
    subject_id INT NOT NULL,                 -- Foreign key referencing
 Here is a possible SQL schema for the educational app with the given requirements:

```
Subject
------
subject_id (primary key)
name
...

Sponsor
-------
sponsor_id (primary key)
name

Ad
--
ad_id (primary key)
sponsor_id (foreign key to Sponsor)
subject_id (foreign key to Subject)
banner (boolean)
interstitial (boolean)