SQL comments - MaxCompute - Alibaba Cloud Documentation Center

To improve code readability, you can write comments in your MaxCompute SQL scripts. This topic describes how to use single-line and multi-line comments in MaxCompute SQL scripts.

Limits

The multi-line comment feature is not available on the DataWorks data development interface.
To use SQL comments in the local client (odpscmd) of the MaxCompute, the odpscmd version must be 0.49.0 or later.
When using single-line comments in the MaxCompute client (odpscmd) or Cloud Shell (odpscmd), a semicolon (;) is required to terminate the comment. Semicolons are not supported in multi-line comments.

Syntax format

Single-line comments

Start single-line comments with --. The syntax is as follows:

-- Comment content

Any text from -- to the end of the line is treated as a comment. You can place the comments on a separate line above the code or at the end of a line of code.

Note

In the SQL analysis interface of the MaxCompute console or the DataWorks data development interface, you can use the Ctrl+/ shortcut to comment out a line of code.

Multi-line comments

For multi-line comments, use /* to begin and */ to end, allowing you to comment out blocks of content at once. The syntax is as follows:

/* 
Comment
content
*/

Important

MaxCompute also supports /*+...*/ as Hint syntax, such as MAPJOIN hints and SKEWJOIN HINT. Hints take precedence over multi-line comments, so ensure the start symbol of the multi-line comment is not mistaken for a Hint start symbol. We recommend that you can use /** as the start symbol for multi-line comments to avoid confusion.

Usage examples

Consider my_table as an existing table. The following codes show the examples of comments:

Example 1: A correct single-line comment.

-- Single-line comment
DESC my_table; -- Single-line comment

Example 2: A correct multi-line comment.

SELECT /* Valid
multi-line
comment
*/ * FROM my_table;

Example 3: An incorrect multi-line comment where /*+ is misinterpreted as the beginning of a Hint.
```
SELECT /*+ Invalid
multi-line
comment
*/ * FROM my_table;
```