PostgreSQL Syntax Explained: A Comprehensive Guide
PostgreSQL syntax is a robust, free relational database management system (RDBMS) which is known for its reliability, feature richness, and extensibility. Being one of the most advanced open-source databases, PostgreSQL syntax is unique in the way that it not only follows standard SQL conventions but also presents different facets being made possible through feature-unique SQL commands, concepts, and syntax.
PostgreSQL allows you to properly store, distribute and work with the data and it is needed, while you will be doing a heavy-duty work using PostgreSQL features. The increasing PostgreSQL usage is traced to its stability and crash-proof features and the fact of being both open-source and free, as stated by the users as the best reasons for using it.
This guide will show you some of the main components of PostgreSQL syntax by giving explicit comments and examples for each. Whether you are new to PostgreSQL syntax or have advanced your skills, this guide will teach you some of the most important and useful commands in PostgreSQL and their uses. The PostgreSQL syntax is broad and entails various topics, including: from the creation of databases and tables to advanced query operations and data manipulation.
We are going to cover in this guide what is the difference between PostgreSQL syntax and other SQL databases, specifically when considering its extra characteristics for performance tuning and fundamental coding. In today’s times when it comes to small or big tasks, doing PostgresSQL syntax right is thus inevitable to be able to work with it effectively and resourcefully.
PostgreSQL syntax is the main point of this article. It helps you to optimize your queries, as well as to maintain your database and to improve your speed of the application. With the help of the whole PostgreSQL syntax, you will be able to tame this powerful relational database management system (RDBMS).
- Database Operations
- Table Operations
- Data Manipulation
- Constraints and Indexes
- Query Operations
- Functions and Procedures
- Joins
- Transactions and Locks
1. Database Operations
- PostgreSQL has its commands to maintain databases at the top of the hierarchy of the database which are the topmost category of a database.
a. Creating a Database
- To create a database within the PostgreSQL database, use the CREATE DATABASE statement. These are the basic syntax:
CREATE DATABASE database_name;
- Example:
CREATE DATABASE mydb;
- This a database named mydb is created.
b. Deleting a Database
- If you wish to remove a database from the server, you can utilize the DROP DATABASE command:
DROP DATABASE database_name;
- Example:
DROP DATABASE mydb;
- The query DELETE also removes the mydb database.
c. Listing Databases
- You can show a collection of all databases available by implementing the following SQL command:
\l
- In another way, if you are using SQL:
SELECT datname FROM pg_database;
2. Table Operations
- Tables are the primary structure in PostgreSQL that are used to classify data.
a. Creating a Table
- In PostgreSQL, you initiate the table by using the CREATE TABLE statement and then giving the table name and column definitions.
CREATE TABLE table_name (
column1 datatype constraints,
column2 datatype constraints,
…
);
- Example:
CREATE TABLE employees (
id SERIAL PRIMARY KEY,
name VARCHAR(100),
age INT,
department VARCHAR(50)
);
- This creates a table employees that have four columns: id, name, age, and department.
b. Altering a Table
- For the ability to change a table that you have, first look at the ALTER TABLE examination.
- The function in the ALTER TABLE instruction may be used for either adding, dropping, or changing the table’s columns when the necessity arises for this.
Add a column:
ALTER TABLE employees ADD COLUMN salary DECIMAL(10, 2);
Modify a column:
ALTER TABLE employees ALTER COLUMN age SET NOT NULL;
Drop a column:
ALTER TABLE employees DROP COLUMN department;
c. Table Deletion
- If you are seeking to wipe out the whole table, the DROP TABLE command is applied:
DROP TABLE employees;
3. Data Manipulation
- The ones are where you can perform operations on the data after creation of tables.
- PostgreSQL employs standard SQL statements like inserting, updating, deleting, and retrieving data transactions.
a. Data Insert
- Put data into a table with the INSERT INTO statement.
INSERT INTO table_name (column1, column2, …)
VALUES (value1, value2, …);
- Example:
INSERT INTO employees (name, age, department)
VALUES (‘John Doe’, 30, ‘Engineering’);
b. Data Update
- You can update the existing data by using the UPDATE statement that includes a SET clause and a WHERE condition to identify which rows to modify.
UPDATE table_name
SET column1 = value1, column2 = value2
WHERE condition;
- Example:
UPDATE employees
SET age = 31
WHERE name = ‘John Doe’;
c. Deleting Data
- To remove data from a table, use the DELETE FROM statement.
DELETE FROM table_name WHERE condition;
- Example:
DELETE FROM employees WHERE id =1;
d. Selecting Data
- The SELECT command is the most widely used SQL command, which retrieves data from one or two tables.
SELECT column1, column2, …
FROM table_name
WHERE condition;
- Example:
SELECT * FROM employees;
- This retrieves all columns and the employees table from the table.
- To limit the number of rows returned, you can use the LIMIT clause:
SELECT * FROM employees LIMIT 5;
4. Constraints and Indexes
- Where PostgreSQL permits you to put restraints and indexes to the tables, therefore, you can guarantee the data integrity and rise the throughput of the query.
a. Primary Key Constraint
- One of the primary keys acts as an enforcer of a unique constraint and prohibits null values from being added into the table.
CREATE TABLE employees (
id SERIAL PRIMARY KEY,
name VARCHAR(100)
);
b. Foreign Key Constraint
- The foreign key is the cause of the connection between two tables.
CREATE TABLE orders (
order_id SERIAL PRIMARY KEY,
employee_id INT,
FOREIGN KEY (employee_id) REFERENCES employees(id)
);
c. Unique Constraint
- It’s a unique constraint that allows the values in a column to differ however it’s that all of them are distinct from each other.
CREATE TABLE products (
product_id SERIAL PRIMARY KEY,
product_name VARCHAR(100) UNIQUE
);
d. Index
- Once you have the index, you can look for more data in the recordset faster because indexes speed up the process in SQL.
CREATE INDEX idx_employee_name ON employees(name);
5. Query Operations
- PostgreSQL contains mainly the sophisticated query functionalities which handle the sorting, grouping, and filtering of data.
a. Sorting Data
- You can achieve result set sorting by incorporating the ORDER BY clause:
SELECT * FROM employees
ORDER BY name ASC;
- This rearranges the employees alphabetically by first in the ascending order of their names. You are also allowed to specify DESC which is for descending order.
b. Grouping Data
- GROUP BY clause specifies which rows should be summarised into one; so, the same-values rows are grouped to short rows, meanwhile, aggregates are computed for the grouped rows.
SELECT department, COUNT(*)
FROM employees
GROUP BY department;
c. Filtering Data
- WHERE clause is used to pick only a part of the returned data by the SELECT statement.
SELECT * FROM employees WHERE age > 30;
- You can also combine the single statement with logical operators such as AND, OR, and NOT.
6. Functions and Procedures
- PostgreSQL is a versatile choice that lets you make a function and a stored procedure so that you can wrap the logic around it.
a. Creating Functions
- You can make certain functions of your own in PostgreSQL by creating the new functions via the script “CREATE FUNCTION.”
CREATE FUNCTION get_employee_count() RETURNS INT AS $$
BEGIN
RETURN (SELECT COUNT(*) FROM employees);
END;
$$ LANGUAGE plpgsql;
b. Calling Functions
- Using the function look like this:
SELECT get_employee_count();
c. Creating Procedures
- Procedures are similar to functions but they are not returning the value.
CREATE PROCEDURE update_salary(emp_id INT, new_salary DECIMAL)
LANGUAGE plpgsql AS $$
BEGIN
UPDATE employees SET salary = new_salary WHERE id = emp_id;
END;
$$;
7. Joins
- Joins are a feature in PostgreSQL that provides the user with an opportunity to combine the rows of a table with those of another table that has a common column based on it.
a. Inner Join
- The INNER JOIN clause is used to select records that have equal values in both tables.
SELECT employees.name, orders.order_id
FROM employees
INNER JOIN orders ON employees.id = orders.employee_id;
b. Left Join
- The LEFT JOIN instruction includes all the rows in the left table while the no corresponding ones on the right table become NULL.
SELECT employees.name, orders.order_id
FROM employees
LEFT JOIN orders ON employees.id = orders.employee_id;
c. Right Join
- The RIGHT JOIN operation is used to include all orders from the right table even if there is no match in the left table.
SELECT employees.name, orders.order_id
FROM employees
RIGHT JOIN orders ON employees.id = orders.employee_id;
d. Full Join
- The FULL JOIN query shows the columns from the tables when they have a common field.
SELECT employees.name, orders.order_id
FROM employees
FULL JOIN orders ON employees.id = orders.employee_id;
8. Transactions and Locks
- PostgreSQL assures transactional integrity and also lets you use transactions for guaranteeing that your database modifications are securely performed.
a. Starting a Transaction
- Get the transaction STARTED: ON committed, run the command that STARTS a transaction in the window.
BEGIN;
b. Committing a Transaction
- Upon the completion of the transaction and the verification of the modifications, you can commit them: (within the notification that the transaction is the last one you get after posting the project).
COMMIT;
c. Rolling Back a Transaction
- In case of an error, you can turn the transaction back to the previous state:
ROLLBACK;
d. Locks
- You are allowed to employ locks to prohibit other transactions from accessing the data you are processing:
BEGIN;
LOCK TABLE employees IN EXCLUSIVE MODE;
— Perform operations
COMMIT;