Re: [SQL] How match percent sign in SELECT using LIKE?

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