Re: [SQL] How match percent sign in SELECT using LIKE? - Mailing list pgsql-sql

At 17:45 +0200 on 15/3/99, Bruce Momjian wrote:


> I have overhauled the LIKE code.  %% is not a literal %, but is the same
> as wildcard %.  Literal % is \%.

This is not SQL 92 compliant, is it? The standard states that if you don't
have an ESCAPE part to the like (i.e. abc LIKE 'bla\%%' ESCAPE '\'), then
there is no escape. I think the correct thing to do is to support the
ESCAPE clause:

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 Format

 <like predicate> ::=
      <match value> [ NOT ] LIKE <pattern>
        [ ESCAPE <escape character> ]

 <match value> ::= <character value expression>

 <pattern> ::= <character value expression>

 <escape character> ::= <character value expression>

[snip]

    a) If an <escape character> is specified, then:

      i) If the length in characters of E is not equal to 1, then
         an exception condition is raised: data exception-invalid
         escape character.

     ii) If there is not a partitioning of the string P into sub-
         strings such that each substring has length 1 or 2, no
         substring of length 1 is the escape character E, and each
         substring of length 2 is the escape character E followed by
         either the escape character E, an <underscore> character,
         or the <percent> character, then an exception condition is
         raised: data exception-invalid escape sequence.

         If there is such a partitioning of P, then in that parti-
         tioning, each substring with length 2 represents a single
         occurrence of the second character of that substring. Each
         substring with length 1 that is the <underscore> character
         represents an arbitrary character specifier. Each substring
         with length 1 that is the <percent> character represents
         an arbitrary string specifier. Each substring with length
         1 that is neither the <underscore> character nor the <per-
         cent> character represents the character that it contains.

    b) If an <escape character> is not specified, then each <under-
      score> character in P represents an arbitrary character spec-
      ifier, each <percent> character in P represents an arbitrary
      string specifier, and each character in P that is neither the
      <underscore> character nor the <percent> character represents
      itself.

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Herouth

--
Herouth Maoz, Internet developer.
Open University of Israel - Telem project
http://telem.openu.ac.il/~herutma