DML SQL

What are the fundamental commands for manipulating data in a SQL database?

DML (Data Manipulation Language) commands are used to perform actions on data within a database. These include inserting, updating, deleting, and selecting data. Understanding DML is crucial for any SQL developer.

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Description

DML statements are the core of interacting with data in a relational database management system (RDBMS). They allow you to modify existing data, add new records, and retrieve information. The most common DML commands are INSERT, UPDATE, DELETE, and SELECT. INSERT is used to add new rows to a table, UPDATE modifies existing rows, and DELETE removes rows. SELECT, while technically a DML command, is often considered separately as it retrieves data without changing the database structure. These commands are essential for tasks like managing customer information, tracking inventory, or analyzing sales data.

Why DML SQL is important

DML is fundamental to any database application. It allows developers to interact with the data, update it, and retrieve information for various reporting and analysis tasks. Without DML, databases would be static and unusable.

DML SQL Example Usage


-- Create a table with a date column
CREATE TABLE Orders (
    OrderID INT PRIMARY KEY,
    OrderDate DATE,
    Amount DECIMAL(10, 2)
);

-- Insert some data
INSERT INTO Orders (OrderID, OrderDate, Amount)
VALUES
(1, '2023-10-26', 100.50),
(2, '2023-11-15', 250.00),
(3, '2023-10-10', 50.00);

-- Query orders placed in October 2023
SELECT OrderID, OrderDate, Amount
FROM Orders
WHERE OrderDate BETWEEN '2023-10-01' AND '2023-10-31';

-- Calculate the difference in days between the first and last orders
SELECT DATEDIFF(DAY, MIN(OrderDate), MAX(OrderDate)) AS OrderDuration
FROM Orders;

-- Extract the year from the OrderDate
SELECT OrderID, YEAR(OrderDate) AS OrderYear
FROM Orders;

-- Format the OrderDate in a specific way
SELECT OrderID, DATE_FORMAT(OrderDate, '%m/%d/%Y') AS formatted_date
FROM Orders;

DML SQL Syntax

Common Mistakes

Forgetting to specify the table and columns when using INSERT or UPDATE.
Using incorrect data types in INSERT statements.
Using incorrect syntax for WHERE clauses in UPDATE and DELETE statements, leading to unintended data modification.
Not understanding the difference between SELECT, INSERT, UPDATE, and DELETE.