SQL comments - MaxCompute - Alibaba Cloud Documentation Center

SQL comments in MaxCompute improve code readability by annotating logic inline. This topic describes how to write single-line and multi-line comments in MaxCompute SQL scripts.

Limitations

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

Syntax

Single-line comments

Start a single-line comment with --. Everything from -- to the end of the line is treated as a comment.

-- Comment content

Place the comment on its own line above the code, or at the end of a line of code.

Note

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

Multi-line comments

Use /* to open and */ to close a multi-line comment, allowing you to comment out a block of content at once.

/*
Comment
content
*/

Important

MaxCompute also supports /*+...*/ as Hint syntax — for example, MAPJOIN hints and SKEWJOIN HINT. Hints take precedence over multi-line comments. To avoid ambiguity, use /** instead of /* as the opening symbol for multi-line comments.

Examples

The following examples use my_table as an existing table.

Single-line comment

The following example shows a single-line comment placed above a statement and at the end of a line:

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

Multi-line comment

The following example shows a multi-line comment embedded in a SELECT statement:

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

Common mistake: `/*+` misinterpreted as a Hint

Opening a multi-line comment with /*+ causes MaxCompute to interpret it as the start of a Hint rather than a comment:

SELECT /*+ Invalid
multi-line
comment
*/ * FROM my_table;

To avoid this, use /** as the opening symbol for multi-line comments.