In SQL, the "not null" constraint is used to ensure that a column in a table cannot have a null value. This means that when a new row is inserted into the table, the specified column must have a value and cannot be left empty. It is a way to enforce data integrity and ensure that important information is always provided for a particular column. If a column is defined as "not null" and an attempt is made to insert a row without providing a value for that column, the database will return an error. **

To prevent displaying null values in SQL, you can use the COALESCE function. COALESCE returns the first non-null expression among its arguments. You can also use the IS NOT NULL condition in the WHERE clause to filter out rows with null values. Another option is to use the CASE statement to replace null values with a specific value or an empty string. **

In database terminology, "not null" means that a column in a table must have a value, and it cannot be empty or null. On the other hand, "null" means that a column can have a missing or unknown value, and it is not required to have a value. In other words, "not null" enforces the presence of a value, while "null" allows for the absence of a value. **

To prevent null values from being displayed in SQL, you can use the IS NOT NULL condition in your query. This condition filters out any rows where the specified column is null. Another approach is to use the COALESCE function to replace null values with a specified default value. Additionally, you can use the WHERE clause to filter out rows with null values before displaying the results. **

To prevent Null values from being displayed in SQL, you can use the IS NOT NULL condition in your WHERE clause when querying the database. This condition filters out any rows where the specified column is Null. Another approach is to use the COALESCE function to replace Null values with a specified default value. Additionally, you can use the CASE statement to handle Null values and display a different value instead. **

The SQL query for the Terra database will depend on the specific task or information you are trying to retrieve. However, a basic SQL query to retrieve all data from a table in the Terra database would look like this: ```sql SELECT * FROM table_name; ``` Replace "table_name" with the actual name of the table you want to retrieve data from. If you want to retrieve specific columns or apply filters, you can modify the query accordingly using the SELECT and WHERE clauses. **

The SQL query for a SQLite database is similar to other SQL databases. Here is an example of a simple SQL query for a SQLite database: ``` SELECT * FROM table_name; ``` This query selects all columns from the specified table in the database. Other common SQL queries for SQLite include INSERT, UPDATE, DELETE, and CREATE TABLE. **

Database normalization is the process of organizing data in a database in a way that reduces redundancy and dependency. It involves breaking down a database into smaller, more manageable tables and defining relationships between them. The goal of normalization is to minimize data redundancy, improve data integrity, and make the database more efficient. There are different levels of normalization, known as normal forms, with each level addressing specific issues related to data organization. **