Fixup of lingo (PR clean) in "-- as the start of a comment" text.

@cindex comments, starting

@cindex starting, comments

Some other SQL databases use @samp{--} to start comments. MySQL

has @samp{#} as the start comment character, even if the @code{mysql}

command-line tool removes all lines that start with @samp{--}.

You can also use the C comment style @code{/* this is a comment */} with

MySQL.

Some other SQL databases use @samp{--} to start comments.

MySQL has @samp{#} as the start comment character. You can also use

the C comment style @code{/* this is a comment */} with MySQL.

@xref{Comments}.

MySQL Version 3.23.3 and above supports the @samp{--} comment style

only if the comment is followed by a space.  This is because this

degenerate comment style has caused many problems with automatically

generated SQL queries that have used something like the following code,

where we automatically insert the value of the payment for

MySQL Version 3.23.3 and above supports the @samp{--} comment style,

provided the comment is followed by a space.  This is because this

comment style has caused many problems with automatically generated

SQL queries that have used something like the following code, where

we automatically insert the value of the payment for

@code{!payment!}:

@example

UPDATE tbl_name SET credit=credit-!payment!

@end example

What do you think will happen when the value of @code{payment} is negative?

Think about what happens if the value of @code{payment} is negative?

Because @code{1--1} is legal in SQL, the consequences of allowing

comments to start with @samp{--} are terrible.

Using our implementation of this method of commenting in MySQL

Version 3.23.3 and up, @code{1-- This is a comment} is actually safe.

Because @code{1--1} is legal in SQL, we think it is terrible that

@samp{--} means start comment.

Another safe feature is that the @code{mysql} command-line client

removes all lines that start with @samp{--}.

In MySQL Version 3.23 you can, however, use:

@code{1-- This is a comment}

The following discussion only concerns you if you are running a MySQL

version earlier than Version 3.23:

The following information is only relevant if you are running a

MySQL version earlier than Version 3.23.3:

If you have a SQL program in a text file that contains @samp{--} comments

you should use:

If you have a SQL program in a text file that contains @samp{--}

comments you should use:

@example

shell> replace " --" " #" < text-file-with-funny-comments.sql \