In the context of databases, a **schema** represents the organizational blueprint of a database. It defines how data is structured and how the relationships between those data entities are established. Here are the key components typically involved in a database schema: 1. **Tables**: These are the fundamental structures that hold data. A table is similar to a spreadsheet where the data is organized in rows and columns. Each column in a table holds a certain type of data (like numbers, dates, or text), and each row holds the data record. 2. **Columns**: Within a table, columns represent the attributes of the data. For example, a table of customer information may include columns for customer ID, name, address, and phone number. 3. **Data Types**: These specify the kind of data that can be stored in a column, such as integers, decimal numbers, strings of text, dates, or boolean values. 4. **Constraints**: These are rules enforced on data in the database. Constraints can ensure the integrity of the data. Common constraints include: - **Primary keys** that uniquely identify a row in a table. - **Foreign keys** that link the rows of one table to those of another. - **Unique constraints** that ensure data in a column (or a group of columns) is unique across the database. - **Not-null constraints** that prevent a column from having a null value. 5. **Relationships**: These define how tables relate to each other. The most common relationships are: - **One-to-one**: Each row in one table is linked to 1 row in another table. - **One-to-many**: Each row in one table can be linked to many rows in another. - **Many-to-many**: Rows in one table can be linked to many rows in another table, and vice versa, usually managed through a third table known as a junction or join table. 6. **Indexes**: These are special lookup tables that the database search engine can use to speed up data retrieval. Simply put, an index in a database is somewhat akin to an index in a book. 7. **Views**: These are virtual tables based on the result-set of an SQL statement. They do not contain data themselves but show data stored in other tables. A schema is crucial because it not only defines a database’s structure but also helps in understanding the logical relationships between different data elements, which is essential for efficient data management and retrieval. [[Idempotent]] [[Cascade Deletions]] [[Reinitializing Alembic and the Database]] [[Monitor PostgreSQL Logs]]