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This article mainly explains the "MySQL single-line comments and multi-line comments methods", the article explains the content is simple and clear, easy to learn and understand, the following please follow the editor's ideas slowly in-depth, together to study and learn "MySQL single-line comments and multi-line comments method"!

In mysql, "-" is a comment character, which means a single-line comment. After the comment character, you need to add a space comment to take effect. The syntax is "--comment content"; both the comment character and the "#" comment character are used for one-line comments, except that there is no need to add spaces after the "#" comment character.

The operating environment of this tutorial: windows10 system, mysql8.0.22 version, Dell G3 computer.

What does it mean in mysql?

MySQL single-line comment

1) A single-line comment can be made with a # comment character, followed by a # comment character. The format is as follows:

# comment content

An example of single-line comments using the comment character # is as follows:

# Delete duplicate lines SELECT DISTINCT product_id and purchase_price FROM Product from the result

2) single-line comments can use-- comment characters,-- you need to add a space after the comment character before the comment can take effect. The format is as follows:

-- comment content

Examples of single-line comments using comment characters-- are as follows:

-- delete duplicate lines SELECT DISTINCT product_id, purchase_price FROM Product from the result

The difference between # and-- is that the content is annotated directly after #, while the second dash of-needs to be annotated with a space character.

MySQL multiline comment

Multiline comments use the / * / comment character. / * for the beginning of the comment content and * / for the end of the comment content. The multiline comment format is as follows:

/ * comment on the first line, comment on the second line * /

Comments are written between / * and * / and can span multiple lines.

Examples of use of multiline comments are as follows

/ * this SELECT statement removes duplicate lines from the result * / SELECT DISTINCT product_id, purchase_price FROM Product

Any comment (single-line comment and multi-line comment) can be inserted in the SQL statement, and the comment can be placed anywhere in the SQL statement.

Insert a single-line comment in the SQL statement, as follows:

SELECT DISTINCT product_id, purchase_price-- removes duplicate rows from the result. FROM Product;SELECT DISTINCT product_id, purchase_price# removes duplicate rows from the result. FROM Product

Insert multiline comments in the SQL statement, as follows:

The SELECT statement SELECT DISTINCT product_id, purchase_price/*, removes duplicate rows from the result. * / FROM Product

Comments can be written in any SQL statement, and there is no limit to the number of comments in the SQL statement.

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