Why should we sometimes use --+ instead of — in SQL injection to comment the rest of the query?

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I have encountered some websites that when I used -- to comment the rest of the query it didn't work, but when I tried --+ it worked.



In the MySQL official documentation there is no such thing as --+ and we only have -- and two other ways:



https://dev.mysql.com/doc/refman/8.0/en/comments.html



Why does this happen (in detail)? I want to know exactly why this works sometimes and -- doesn't, and why there is no --+ for comments in the MySQL man page?






http sql-injection mysql







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  • 1




    I suppose your question is more related to HTTP than to SQL...
    – Your Common Sense
    11 hours ago






  • 2




    @YourCommonSense i had no idea its related to HTTP and not SQL, so why this happens?
    – Richard Jones
    11 hours ago










  • You can also use # which doesn't need a space after
    – paj28
    10 hours ago














up vote
9
down vote

favorite












I have encountered some websites that when I used -- to comment the rest of the query it didn't work, but when I tried --+ it worked.



In the MySQL official documentation there is no such thing as --+ and we only have -- and two other ways:



https://dev.mysql.com/doc/refman/8.0/en/comments.html



Why does this happen (in detail)? I want to know exactly why this works sometimes and -- doesn't, and why there is no --+ for comments in the MySQL man page?






http sql-injection mysql







share|improve this question



















  • 1




    I suppose your question is more related to HTTP than to SQL...
    – Your Common Sense
    11 hours ago






  • 2




    @YourCommonSense i had no idea its related to HTTP and not SQL, so why this happens?
    – Richard Jones
    11 hours ago










  • You can also use # which doesn't need a space after
    – paj28
    10 hours ago












up vote
9
down vote

favorite









up vote
9
down vote

favorite











I have encountered some websites that when I used -- to comment the rest of the query it didn't work, but when I tried --+ it worked.



In the MySQL official documentation there is no such thing as --+ and we only have -- and two other ways:



https://dev.mysql.com/doc/refman/8.0/en/comments.html



Why does this happen (in detail)? I want to know exactly why this works sometimes and -- doesn't, and why there is no --+ for comments in the MySQL man page?






http sql-injection mysql







share|improve this question















I have encountered some websites that when I used -- to comment the rest of the query it didn't work, but when I tried --+ it worked.



In the MySQL official documentation there is no such thing as --+ and we only have -- and two other ways:



https://dev.mysql.com/doc/refman/8.0/en/comments.html



Why does this happen (in detail)? I want to know exactly why this works sometimes and -- doesn't, and why there is no --+ for comments in the MySQL man page?






http sql-injection mysql




http sql-injection mysql






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share|improve this question













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edited 18 mins ago









Boann

1795




1795










asked 11 hours ago









Richard Jones

543




543







  • 1




    I suppose your question is more related to HTTP than to SQL...
    – Your Common Sense
    11 hours ago






  • 2




    @YourCommonSense i had no idea its related to HTTP and not SQL, so why this happens?
    – Richard Jones
    11 hours ago










  • You can also use # which doesn't need a space after
    – paj28
    10 hours ago












  • 1




    I suppose your question is more related to HTTP than to SQL...
    – Your Common Sense
    11 hours ago






  • 2




    @YourCommonSense i had no idea its related to HTTP and not SQL, so why this happens?
    – Richard Jones
    11 hours ago










  • You can also use # which doesn't need a space after
    – paj28
    10 hours ago







1




1




I suppose your question is more related to HTTP than to SQL...
– Your Common Sense
11 hours ago




I suppose your question is more related to HTTP than to SQL...
– Your Common Sense
11 hours ago




2




2




@YourCommonSense i had no idea its related to HTTP and not SQL, so why this happens?
– Richard Jones
11 hours ago




@YourCommonSense i had no idea its related to HTTP and not SQL, so why this happens?
– Richard Jones
11 hours ago












You can also use # which doesn't need a space after
– paj28
10 hours ago




You can also use # which doesn't need a space after
– paj28
10 hours ago










1 Answer
1






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From the documentation:




From a -- sequence to the end of the line. In MySQL, the -- (double-dash) comment style requires the second dash to be followed by at least one whitespace or control character (such as a space, tab, newline, and so on). This syntax differs slightly from standard SQL comment syntax, as discussed in Section 1.8.2.4, “'--' as the Start of a Comment”.




(emphasis mine)



Many URL decoders treat + as a space.






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    up vote
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    down vote













    From the documentation:




    From a -- sequence to the end of the line. In MySQL, the -- (double-dash) comment style requires the second dash to be followed by at least one whitespace or control character (such as a space, tab, newline, and so on). This syntax differs slightly from standard SQL comment syntax, as discussed in Section 1.8.2.4, “'--' as the Start of a Comment”.




    (emphasis mine)



    Many URL decoders treat + as a space.






    share|improve this answer
























      up vote
      23
      down vote













      From the documentation:




      From a -- sequence to the end of the line. In MySQL, the -- (double-dash) comment style requires the second dash to be followed by at least one whitespace or control character (such as a space, tab, newline, and so on). This syntax differs slightly from standard SQL comment syntax, as discussed in Section 1.8.2.4, “'--' as the Start of a Comment”.




      (emphasis mine)



      Many URL decoders treat + as a space.






      share|improve this answer






















        up vote
        23
        down vote










        up vote
        23
        down vote









        From the documentation:




        From a -- sequence to the end of the line. In MySQL, the -- (double-dash) comment style requires the second dash to be followed by at least one whitespace or control character (such as a space, tab, newline, and so on). This syntax differs slightly from standard SQL comment syntax, as discussed in Section 1.8.2.4, “'--' as the Start of a Comment”.




        (emphasis mine)



        Many URL decoders treat + as a space.






        share|improve this answer












        From the documentation:




        From a -- sequence to the end of the line. In MySQL, the -- (double-dash) comment style requires the second dash to be followed by at least one whitespace or control character (such as a space, tab, newline, and so on). This syntax differs slightly from standard SQL comment syntax, as discussed in Section 1.8.2.4, “'--' as the Start of a Comment”.




        (emphasis mine)



        Many URL decoders treat + as a space.







        share|improve this answer












        share|improve this answer



        share|improve this answer










        answered 10 hours ago









        AndrolGenhald

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