Create column-reference for PostgreSQL.

content/postgresql/concepts/column-references/column-references.md

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+---
+Title: 'Column References'
+Description: 'Allow developers to retrieve column names and relevant data from a table.'
+Subjects:
+  - 'Computer Science'
+  - 'Data Science'
+Tags:
+  - 'PostgreSQL'
+  - 'Database'
+  - 'Data'
+CatalogContent:
+  - 'getting-started-off-platform-for-data-science'
+  - 'paths/design-databases-with-postgresql'
+---
+
+In PostgreSQL, **column references** is an important concept that allows developers to retrieve column names and relevant data from a table. Understanding this concept can be useful for data scientists, analysts and administrators as it helps them to query and analyze data efficiently.
+
+## Syntax
+
+The process for referencing columns in PostgreSQL matches a lot with that of SQL (Structured Query Language) as they share some attributes and patterns. Specifically, there are some statements that can be used to reference columns in PostgreSQL.
+
+### SELECT
+
+The `SELECT` statement is used to get data from specific columns in a table:
+
+```pseudo
+SELECT column3, column2, ...
+FROM table_name;
+```
+
+### INSERT
+
+The `INSERT` statement is used to specify the columns to which data is to be inserted:
+
+```pseudo
+INSERT INTO table_name (column3, column7, ...)
+VALUES (value3, value7, ...);
+```
+
+### UPDATE
+
+The `UPDATE` statement is used to specify the columns to be updated with new data:
+
+```pseudo
+UPDATE table_name
+SET column4 = value4, column9 = value9, ...
+WHERE condition;
+```
+
+### DELETE
+
+The `DELETE` statement is used to specify the columns to be deleted:
+
+```pseudo
+DELETE FROM table_name
+WHERE condition;
+```
+
+### ALTER TABLE
+
+The `ALTER TABLE` statement is used to add, modify or remove columns from a table.
+
+Here is the syntax for adding a column to a table:
+
+```pseudo
+ALTER TABLE table_name
+ADD column_name data_type;
+```
+
+The following syntax shows how to modify a column in a table:
+
+```pseudo
+ALTER TABLE table_name
+ALTER COLUMN column_name TYPE new_data_type;
+```
+
+The syntax for removing a column from a table is following:
+
+```pseudo
+ALTER TABLE table_name
+DROP COLUMN column_name;
+```
+
+### CREATE TABLE
+
+The `CREATE TABLE` statement is used to define columns while creating a table:
+
+```pseudo
+CREATE TABLE table_name (
+column1 data_type,
+column2 data_type,
+);
+```
+
+## Example
+
+The following example demonstrates the usage of column references in PostgreSQL:
+
+```sql
+-- Creating a table
+
+CREATE TABLE bus (
+  first_name VARCHAR(80),
+  last_name VARCHAR(80),
+  occupation VARCHAR(80),
+  starting_point VARCHAR(80),
+  destination_point VARCHAR(80),
+  ticket_price INTEGER,
+  duration_in_minutes BIGINT,
+  type_of_payment VARCHAR(90),
+  age INTEGER,
+  next_of_kin VARCHAR(100),
+  date_of_payment DATE
+);
+
+-- Inserting data
+
+INSERT INTO bus (first_name, last_name, occupation, starting_point, destination_point, ticket_price, duration_in_minutes, type_of_payment, age, next_of_kin, date_of_payment)
+
+VALUES
+  ('Ikechukwu', 'Ogumba', 'Student', 'Dei-Dei', 'Kubwa', 200, 15, 'Card Payment', 22, 'William Ogumba', '2024-04-20'),
+  ('John', 'Snow', 'Plumber', 'Dei-Dei', 'Wuse Junction', 500, 40, 'Card Payment', 30, 'Micheal Bolton', '2024-04-20'),
+  ('Barry', 'Hickler', 'Banker', 'Dei-Dei', 'Berger', 700, 60, 'Cash Payment', 39, 'James Rashford', '2024-04-20'),
+  ('Jenny', 'Simpson', 'Therapist', 'Dei-Dei', 'Maitama', 800, 80, 'Card Payment', 30, 'Julie Simpson', '2024-04-20'),
+  ('Junior', 'Kelechukwu', 'Student', 'Dei-Dei', 'Kubwa', 200, 15, 'Card Payment', 40, 'Matthew Kelechukwu', '2024-04-20'),
+  ('Folakemi', 'Abimbola', 'Pastor', 'Dei-Dei', 'Wuse Junction', 500, 40, 'Cash', 30, 'Kehinde Abimbola', '2024-04-20'),
+  ('Tochukwu', 'Okafor', 'Athlete', 'Dei-Dei', 'Berger', 700, 60, 'Card Payment', 39, 'Duru Okafor', '2024-04-20'),
+  ('Taiwo', 'Kehinde', 'Trader', 'Dei-Dei', 'Kubwa', 200, 15, 'Card Payment', 50, 'Adebayo Kehinde', '2024-04-20');
+
+SELECT
+  first_name,
+  last_name,
+  age
+
+FROM
+  bus;
+```
+
+The above code lists the first name, last name and age of all the passengers in the bus.