# Comments

This document describes the comment syntax supported by MatrixOne.

MatrixOne supports the following annotation formats:

- Use `#` comments:

   ```text
   mysql> select 100-99; # Comment content
   +-------------+
   | 100 - 99 |
   +-------------+
   | 1 |
   +-------------+
   1 row in set (0.01 sec)
   ```

- Use `--` to comment a line. `--` (double dash) comment style requires that the second dash be followed by at least one space or control character (such as spaces, tabs, line breaks, etc.).

   ```text
   mysql> select 100-99; -- Comment content
   +-------------+
   | 100 - 99 |
   +-------------+
   | 1 |
   +-------------+
   1 row in set (0.01 sec)
   ```

- The comment content starts with `/*` and ends with `*/`, the same way it is used in C. This syntax allows comments to be extended to multiple lines.

   ```text
   mysql> select 100 /* Comment content */ -99;
   +-------------+
   | 100 - 99 |
   +-------------+
   | 1 |
   +-------------+
   1 row in set (0.01 sec)
   ```

   or:

   ```text
   mysql> select 100
   /*
   Comment content
   */
   -99;
   +-------------+
   | 100 - 99 |
   +-------------+
   | 1 |
   +-------------+
   1 row in set (0.01 sec)
   ```

## MatrixOne Executable Annotation Syntax

- MatrixOne supports C language annotation format:

```text
mysql> select 100-99; // This comment continues to the end of line
+-------------+
| 100 - 99 |
+-------------+
| 1 |
+-------------+
1 row in set (0.03 sec)
```

or:

```text
mysql> // This comment continues to the line
    -> select 100-99;
+-------------+
| 100 - 99 |
+-------------+
| 1 |
+-------------+
```

- C language annotation formats that MatrixOne does not support:

```text
mysql> select 100 /*! Specific code */ -99;
ERROR 1064 (HY000): SQL parser error: You have an error in your SQL syntax; check the manual that corresponds to your MatrixOne server version for the right syntax to use. syntax error at line 1 column 28 near " code */ -99";
```

or:

```text
mysql> select 100 /*!50110 Specific code */ -99;
ERROR 1064 (HY000): SQL parser error: You have an error in your SQL syntax; check the manual that corresponds to your MatrixOne server version for the right syntax to use. syntax error at line 1 column 33 near " code */ -99";
```

## limit

- MatrixOne does not support nested annotations yet.