The CHECK keyword is a constraint that limits the value that can be placed in a column.

The CONSTRAINT keyword is used to create or delete a constraint from an existing table.

The DEFAULT keyword provides a default value for a column that will be added to all new records if no other value is specified.

The DROP keyword is used to delete existing columns, constraints, databases, indexes, tables, and views.

The FOREIGN KEY keywords are a key (a field or fields in one table that refers to the PRIMARY KEY in another table) used to link two tables together.

Indexes are used to speed up the retrieval of data (searches/queries) from the database.

The LIMIT keyword is used to specify the number of records to return (MySQL).

The PRIMARY KEY keywords uniquely identifies each record in a table, which can have only one primary key consisting of a single field or multiple fields.

The TOP keyword is used to specify the number of records to return (SQL Server).

The UNIQUE keyword ensures that all values in a column are unique.