How do you comment SQL code in different database systems?

SQL code comments are essential for adding explanations, notes, or descriptions within your SQL code to make it more understandable for developers and maintainers. The method for adding comments in SQL code may vary slightly among different database systems.

Here's how you can comment SQL code in some popular database systems:

1. SQL Server (Transact-SQL):

• Single-Line Comment: Use -- followed by your comment.

  -- This is a single-line comment
  SELECT * FROM TableName;
  

• Multi-Line Comment: Enclose your comment within /* and */

  /* 
     This is a multi-line comment.
     It can span multiple lines.
  */
  SELECT * FROM TableName;
  

2. MySQL:

• Single-Line Comment: Use -- followed by your comment.

  -- This is a single-line comment
  SELECT * FROM TableName;
  

• Multi-Line Comment: Enclose your comment within /* and */.

  /* 
     This is a multi-line comment.
     It can span multiple lines.
  */
  SELECT * FROM TableName;
  

3. PostgreSQL:

• Single-Line Comment: Use -- followed by your comment.

  -- This is a single-line comment
  SELECT * FROM TableName;
  

• Multi-Line Comment: Enclose your comment within /* and */.

  /* 
     This is a multi-line comment.
     It can span multiple lines.
  */
  SELECT * FROM TableName;
  

4. Oracle Database:

• Single-Line Comment: Use -- followed by your comment.

  -- This is a single-line comment
  SELECT * FROM TableName;
  

• Multi-Line Comment: Enclose your comment within /* and */.

  /* 
     This is a multi-line comment.
     It can span multiple lines.
  */
  SELECT * FROM TableName;
  

5. SQLite:

• SQLite supports both single-line and multi-line comments using the same syntax as mentioned above for other database systems.

6. IBM Db2:

• Single-Line Comment: Use -- followed by your comment.

  -- This is a single-line comment
  SELECT * FROM TableName;
  

• Multi-Line Comment: Enclose your comment within /* and */.

  /* 
     This is a multi-line comment.
     It can span multiple lines.
  */
  SELECT * FROM TableName;
  

7. Microsoft Access:

• Microsoft Access supports both single-line and multi-line comments using the same syntax as mentioned above for SQL Server.

8. Snowflake:

• Snowflake supports both single-line and multi-line comments using the same syntax as mentioned above for other database systems.

In summary, the most common way to comment SQL code in various database systems is to use -- for single-line comments and /* ... */ for multi-line comments. However, some systems may have slight variations or additional comment styles, so it's essential to consult the documentation of the specific database system you are working with for any unique comment conventions.