What does column mean in sql?

In a SQL database, a column is a field that stores data vertically, with a unique name and a specified data type. Columns include: column name, data type, constraints, and default values. Columns are used to organize data and ensure data integrity through constraints. Columns can be created with the CREATE TABLE statement and manipulated with the ALTER TABLE statement, including adding, deleting, modifying, and querying data.

Column in SQL

In SQL database, a column is a vertical field in a table that stores a specific A collection of type data. Each column has a unique name and specifies the type of data that can be stored in the column.

Parts of a column

• Column name: A unique name used to identify the column.
• Data type: Specify the type of data that can be stored in the column, such as text, number, date, or Boolean value.
• Constraints: Apply restrictions on the data that can be stored in the column, such as uniqueness, non-nullability, and range.
• Default value: When a new row is inserted into the table, the default value assigned to the column if no value is specified.

Importance of Columns

Columns are crucial for organizing data in a table. They allow users to sort, group, and filter data by specific fields. Additionally, column constraints ensure data integrity and prevent invalid or inconsistent data from entering the table.

How to create columns

When creating a new table, you can create columns explicitly by using the CREATE TABLE statement. For example:

<code class="sql">CREATE TABLE employees (
  id INT NOT NULL PRIMARY KEY,
  name VARCHAR(255) NOT NULL,
  email VARCHAR(255) UNIQUE
);</code>

In this example, table employees has three columns:

• id is a unique identifier column that stores integers data.
• name is a text column that can store up to 255 characters.
• email is a unique text column that can store up to 255 characters.

How to operate columns

You can perform various operations on columns, such as:

• Add a column:Use the ALTER TABLE statement to add new columns to an existing table.
• Delete a column: Use the ALTER TABLE statement to delete a column from an existing table.
• Modify columns: Use the ALTER TABLE statement to change the name, data type, or constraints of a column.
• Query data: Use the SELECT statement to retrieve data from a column.
• Update data: Use the UPDATE statement to update the data in the column.

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