Learn CQL with Real Code Examples

CREATE TABLE users (
    id UUID PRIMARY KEY,
    name TEXT,
    age INT
);

INSERT INTO users (id, name, age)
VALUES (uuid(), 'Alice', 30);

SELECT name, age FROM users
WHERE age > 25;

Examples of creating a table, inserting data, and querying in Cassandra using CQL.

-- Select all rows
SELECT * FROM employees;

-- Select with condition
SELECT name, salary FROM employees WHERE salary > 50000;

-- Sort results
SELECT * FROM employees ORDER BY hire_date DESC;

Basic MySQL queries for selecting rows with filters and sorting.

CREATE TABLE products (
    id SERIAL PRIMARY KEY,
    name TEXT NOT NULL,
    price NUMERIC
);

INSERT INTO products (name, price)
VALUES ('Laptop', 1200.50),
       ('Phone', 699.99);

SELECT * FROM products;

Creating a table and inserting rows in PostgreSQL.

// Find all users
 db.users.find({})

// Find by condition
 db.users.find({ age: { $gte: 21 } })

// Aggregation: group by role
 db.users.aggregate([
    { $group: { _id: "$role", total: { $sum: 1 } } }
])

Examples of find, projection, and aggregation in MongoDB.

CREATE TABLE books (
    id INTEGER PRIMARY KEY AUTOINCREMENT,
    title TEXT,
    author TEXT
);

INSERT INTO books (title, author)
VALUES ('1984', 'George Orwell');

SELECT * FROM books;

Creating a table, inserting values, and running queries in SQLite.

# Set and Get
SET session:1 "active"
GET session:1

# Hash example
HSET user:1 name "Alice" age "30"
HGETALL user:1

# List example
LPUSH queue task1 task2
LRANGE queue 0 -1

Common Redis commands for strings, hashes, and lists.

// Create nodes
CREATE (a:Person {name: "Alice"}), (b:Person {name: "Bob"});

// Create relationship
MATCH (a:Person {name: "Alice"}), (b:Person {name: "Bob"})
CREATE (a)-[:FRIEND]->(b);

// Query
MATCH (p:Person)-[:FRIEND]->(f)
RETURN p.name, f.name;

Creating nodes, relationships, and querying with Cypher in Neo4j.

{
    "query": {
        "match": {
        title: "database"
        }
    }
}

{
    "query": {
        "range": {
        "year": { "gte": 2020 }
        }
    }
}

Performing search queries using Elasticsearch Query DSL.

-- Insert temperature reading
INSERT temperature,location=room1 value=24.5

-- Query last hour
SELECT value FROM temperature WHERE time > now() - 1h;

-- Group by 5 minutes
SELECT MEAN(value) FROM temperature
WHERE time > now() - 1d GROUP BY time(5m);

Using InfluxQL for inserting and querying time-series data.

DECLARE
    v_name VARCHAR2(50) := 'Alice';
    v_age NUMBER := 30;
BEGIN
    DBMS_OUTPUT.PUT_LINE('Name: ' || v_name || ', Age: ' || v_age);
END;

Example of a PL/SQL block with variable declaration and output.