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Fix issues around strictness of SIMILAR TO.

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As a result of some long-ago quick hacks, the SIMILAR TO operator
and the corresponding flavor of substring() interpreted "ESCAPE NULL"
as selecting the default escape character '\'.  This is both
surprising and not per spec: the standard is clear that these
functions should return NULL for NULL input.

Additionally, because of inconsistency of the strictness markings
of 3-argument substring() and similar_escape(), the planner could not
inline the SQL definition of substring(), resulting in a substantial
performance penalty compared to the underlying POSIX substring()
function.

The simplest fix for this would be to change the strictness marking
of similar_escape(), but if we do that we risk breaking existing views
that depend on that function.  Hence, leave similar_escape() as-is
as a compatibility function, and instead invent a new function
similar_to_escape() that comes in two strict variants.

There are a couple of other behaviors in this area that are also
not per spec, but they are documented and seem generally at least
as sane as the spec's definition, so leave them alone.  But improve
the documentation to describe them fully.

Patch by me; thanks to Álvaro Herrera and Andrew Gierth for review
and discussion.

Discussion: https://postgr.es/m/14047.1557708214@sss.pgh.pa.us
This commit is contained in:
Tom Lane
2019-09-07 14:21:59 -04:00
parent c5bc7050af
commit ca70bdaefe
7 changed files with 193 additions and 41 deletions
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16
src/backend/parser/gram.y
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@ -13073,15 +13073,15 @@ a_expr: c_expr { $$ = $1; }
| a_expr SIMILAR TO a_expr %prec SIMILAR
{
FuncCall *n = makeFuncCall(SystemFuncName("similar_escape"),
list_make2($4, makeNullAConst(-1)),
FuncCall *n = makeFuncCall(SystemFuncName("similar_to_escape"),
list_make1($4),
@2);
$$ = (Node *) makeSimpleA_Expr(AEXPR_SIMILAR, "~",
$1, (Node *) n, @2);
}
| a_expr SIMILAR TO a_expr ESCAPE a_expr %prec SIMILAR
{
FuncCall *n = makeFuncCall(SystemFuncName("similar_escape"),
FuncCall *n = makeFuncCall(SystemFuncName("similar_to_escape"),
list_make2($4, $6),
@2);
$$ = (Node *) makeSimpleA_Expr(AEXPR_SIMILAR, "~",
@ -13089,15 +13089,15 @@ a_expr: c_expr { $$ = $1; }
}
| a_expr NOT_LA SIMILAR TO a_expr %prec NOT_LA
{
FuncCall *n = makeFuncCall(SystemFuncName("similar_escape"),
list_make2($5, makeNullAConst(-1)),
FuncCall *n = makeFuncCall(SystemFuncName("similar_to_escape"),
list_make1($5),
@2);
$$ = (Node *) makeSimpleA_Expr(AEXPR_SIMILAR, "!~",
$1, (Node *) n, @2);
}
| a_expr NOT_LA SIMILAR TO a_expr ESCAPE a_expr %prec NOT_LA
{
FuncCall *n = makeFuncCall(SystemFuncName("similar_escape"),
FuncCall *n = makeFuncCall(SystemFuncName("similar_to_escape"),
list_make2($5, $7),
@2);
$$ = (Node *) makeSimpleA_Expr(AEXPR_SIMILAR, "!~",
@ -14323,9 +14323,9 @@ subquery_Op:
| NOT_LA ILIKE
{ $$ = list_make1(makeString("!~~*")); }
/* cannot put SIMILAR TO here, because SIMILAR TO is a hack.
* the regular expression is preprocessed by a function (similar_escape),
* the regular expression is preprocessed by a function (similar_to_escape),
* and the ~ operator for posix regular expressions is used.
* x SIMILAR TO y -> x ~ similar_escape(y)
* x SIMILAR TO y -> x ~ similar_to_escape(y)
* this transformation is made on the fly by the parser upwards.
* however the SubLink structure which handles any/some/all stuff
* is not ready for such a thing.