DQL, DML, DDL, DCL and TCL

Q. What are DDL, DQL, DML, DCL and TCL Commands?

In SQL (Structured Query Language), commands are categorized into 5 main types based on their functionality.

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1. Data Query Language (DQL)

DQL is used for querying the database and retrieving data.

SELECT: Retrieves data from one or more tables.
```
SELECT FirstName, LastName
FROM Employees;
```

2. Data Manipulation Language (DML)

DML commands are used to manipulate data within existing database objects.

INSERT: Adds new records to a table.

INSERT INTO Employees (EmployeeID, FirstName, LastName, Age)
VALUES (1, 'John', 'Doe', 30);

UPDATE: Modifies existing records in a table.

UPDATE Employees
SET Age = 31
WHERE EmployeeID = 1;

DELETE: Removes records from a table.

DELETE FROM Employees
WHERE EmployeeID = 1;

3. Data Definition Language (DDL)

DDL commands are used to define and modify database structures such as schemas, tables, indexes, and views.

CREATE: Creates a new table, view, index, or database.

CREATE TABLE Employees (
    EmployeeID int,
    FirstName varchar(255),
    LastName varchar(255),
    Age int
);