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SQL Syntax

SQL (Structured Query Language) is used to manage and manipulate relational databases. Below are some of the key SQL syntax components:

1. Data Definition Language (DDL)

CREATE TABLE: Creates a new table in the database.

CREATE TABLE table_name (
  column1 datatype constraint,
  column2 datatype constraint,
  ...
);

ALTER TABLE: Modifies an existing table.

ALTER TABLE table_name
ADD column_name datatype constraint;

ALTER TABLE table_name
DROP COLUMN column_name;

ALTER TABLE table_name
MODIFY column_name new_datatype;

DROP TABLE: Deletes a table and all of its data.
```
DROP TABLE table_name;
```

2. Data Manipulation Language (DML)

INSERT INTO: Inserts new data into a table.

INSERT INTO table_name (column1, column2, ...)
VALUES (value1, value2, ...);

UPDATE: Updates existing data within a table.

UPDATE table_name
SET column1 = value1, column2 = value2, ...
WHERE condition;

DELETE: Deletes data from a table.

DELETE FROM table_name
WHERE condition;

3. Data Query Language (DQL)

SELECT: Retrieves data from the database.

SELECT column1, column2, ...
FROM table_name
WHERE condition
GROUP BY column
HAVING condition
ORDER BY column
LIMIT number;

Examples:

Basic Select:
```
SELECT * FROM employees;
```

Select with conditions:

SELECT name, salary FROM employees WHERE department = 'Sales';

4. Data Control Language (DCL)

GRANT: Gives user access privileges to the database.
```
GRANT privilege_name ON object TO user;
```
REVOKE: Withdraws user access privileges given by the GRANT command.
```
REVOKE privilege_name ON object FROM user;
```

5. Transaction Control Language (TCL)

COMMIT: Saves the transaction permanently in the database.
```
COMMIT;
```
ROLLBACK: Undoes transactions that have not been saved to the database.
```
ROLLBACK;
```
SAVEPOINT: Sets a point within a transaction to which a rollback can be performed.
```
SAVEPOINT savepoint_name;
```
SET TRANSACTION: Sets the characteristics of the current transaction.
```
SET TRANSACTION [read write | read only];
```

6. Joins

INNER JOIN: Selects records that have matching values in both tables.

SELECT columns
FROM table1
INNER JOIN table2
ON table1.column = table2.column;

LEFT JOIN (or LEFT OUTER JOIN): Selects all records from the left table and the matched records from the right table.
```
SELECT columns
FROM table1
LEFT JOIN table2
ON table1.column = table2.column;
```
RIGHT JOIN (or RIGHT OUTER JOIN): Selects all records from the right table and the matched records from the left table.
```
SELECT columns
FROM table1
RIGHT JOIN table2
ON table1.column = table2.column;
```
FULL JOIN (or FULL OUTER JOIN): Selects all records when there is a match in either left or right table.
```
SELECT columns
FROM table1
FULL JOIN table2
ON table1.column = table2.column;
```

Example Database Table Creation

Let's say we want to create a database table for storing information about employees:

CREATE TABLE employees (
    employee_id INT PRIMARY KEY,
    first_name VARCHAR(50) NOT NULL,
    last_name VARCHAR(50) NOT NULL,
    email VARCHAR(100) UNIQUE,
    hire_date DATE NOT NULL,
    job_id VARCHAR(10) NOT NULL,
    salary DECIMAL(10, 2),
    department_id INT
);

With these basic SQL commands and syntax, you can effectively manage and manipulate data within a relational database. If you need further details or specific examples, feel free to ask!

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