Fundamental SQL concepts

Hi guys, this is the first day I learn IT (officially). I decide to take notes about whatever I think important and related. Hopefully I can form a network of knowledge one day.
It would be so ideal if someone read my posts and help me improve. All suggestions are welcomed. Learning is detemined to be a road of loneliness, but one will go further with other lonely geeks. That's what I thought the meaning of communities.

1. SELECT Statement:

• The SELECT statement is used to retrieve data from one or more tables.

   SELECT column1, column2
   FROM table_name;

2. FROM Clause:

• The FROM clause specifies the table or tables from which to retrieve data.

   SELECT column1, column2
   FROM employees;

3. WHERE Clause:

• The WHERE clause is used to filter rows based on specific conditions.

   SELECT column1, column2
   FROM table_name
   WHERE condition;

4. AND, OR, NOT Operators:

• Combine conditions using AND, OR, and NOT operators in the WHERE clause.

   SELECT column1, column2
   FROM table_name
   WHERE condition1 AND condition2;

5. ORDER BY Clause:

• The ORDER BY clause is used to sort the result set based on one or more columns.

   SELECT column1, column2
   FROM table_name
   ORDER BY column1 ASC;

6. INSERT INTO Statement:

• The INSERT INTO statement is used to insert new records into a table.

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

7. UPDATE Statement:

• The UPDATE statement is used to modify existing records in a table.

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

8. DELETE Statement:

• The DELETE statement is used to remove records from a table.

   DELETE FROM table_name
   WHERE condition;

9. JOIN Clause:

• The JOIN clause is used to combine rows from two or more tables based on a related column.

   SELECT column1, column2
   FROM table1
   INNER JOIN table2 ON table1.column = table2.column;

10. GROUP BY Clause:

- The `GROUP BY` clause is used to group rows based on one or more columns, often used with aggregate functions.

```sql
SELECT column1, COUNT(*)
FROM table_name
GROUP BY column1;
```

11. HAVING Clause:

- The `HAVING` clause is used with the `GROUP BY` clause to filter the results based on aggregate values.

```sql
SELECT column1, COUNT(*)
FROM table_name
GROUP BY column1
HAVING COUNT(*) > 10;
```

12. Aliases:

- Use aliases to provide temporary names for columns or tables in your queries.

```sql
SELECT column1 AS alias1, column2 AS alias2
FROM table_name;
```

13. Comments:

- Use `--` for single-line comments or `/* */` for multi-line comments.

```sql
-- This is a single-line comment

/*
This is a
multi-line comment
*/
```