Search code examples
sqlcomments

Are there multiline comment delimiters in SQL that are vendor-agnostic?


While editing, building up, or cherry picking from SQL statements I can find myself interacting with one of four popular database tools.

I have been resorting to single line commenting for DB2 and Informix. I have created macros in Vim to make this slightly more efficient, but I was wondering if I am working too hard.


Solution

  • C style comments are standard in SQL 2003 and SQL 2008 (but not in SQL 1999 or before). The following DBMS all support C style comments:

    • Informix
    • PostgreSQL
    • MySQL
    • Oracle
    • DB2
    • Sybase
    • Ingres
    • Microsoft SQL Server
    • SQLite (3.7.2 and later)
    • Teradata and Aster

    That is not every possible DBMS, but it is more or less every major SQL DBMS. (I'll willingly add notes about any other DBMS that does - or does not - support C style comments.)

    The SQL 2003 standard documents comment notations thus:

    <comment> ::= <simple comment> | <bracketed comment>
    
    <simple comment> ::=
        <simple comment introducer> [ <comment character> ... ] <newline>
    
    <simple comment introducer> ::=
        <minus sign> <minus sign> [ <minus sign> ... ]
    
    <bracketed comment> ::=
        <bracketed comment introducer> <bracketed comment contents>
        <bracketed comment terminator>
    
    <bracketed comment introducer> ::= <slash> <asterisk>
    
    <bracketed comment terminator> ::= <asterisk> <slash>
    
    <bracketed comment contents> ::= [ { <comment character> | <separator> }... ]
    
    <comment character> ::= <nonquote character> | <quote>
    

    IBM Informix Dynamic Server (IDS or Informix) supports C style comments. It also supports '{ ... }' as potentially multi-line comments, except in contexts where it means something else - that something else being a LIST or SET or MULTISET literal. (You might find that DB-Access gets confused by C style comments; that is a separate issue.)