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Commit28a61fc

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Remove precedence hacks no longer needed without postfix operators.
It's no longer necessary to assign explicit precedences to GENERATED,NULL_P, PRESERVE, or STRIP_P.Actually, we don't need to assign precedence to IDENT either; that wasreally just there to govern the behavior of target_el's "a_expr IDENT"production, which no longer ends with that terminal. However, it seemslike a good idea to continue to do so, because it provides a referencepoint for a precedence level that we can assign to other unreservedkeywords that lack a natural precedence level.Research by Peter Eisentraut and John Naylor; comment rewrite by me.Discussion:https://postgr.es/m/38ca86db-42ab-9b48-2902-337a0d6b8311@2ndquadrant.com
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‎src/backend/parser/gram.y

Lines changed: 15 additions & 19 deletions
Original file line numberDiff line numberDiff line change
@@ -744,22 +744,15 @@ static Node *makeRecursiveViewSelect(char *relname, List *aliases, Node *query);
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%nonassocBETWEENIN_PLIKEILIKESIMILARNOT_LA
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%nonassocESCAPE/* ESCAPE must be just above LIKE/ILIKE/SIMILAR*/
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/*
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* To support target_el without AS, we must give IDENT an explicit priority
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* between ESCAPE and Op. We can safely assign the same priority to
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* various unreserved keywords as needed to resolve ambiguities (this can't
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* have any bad effects since obviously the keywords will still behave the
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* same as if they weren't keywords). We need to do this:
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* for PARTITION, RANGE, ROWS, GROUPS to support opt_existing_window_name;
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* for RANGE, ROWS, GROUPS so that they can follow a_expr without creating
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* postfix-operator problems;
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* for GENERATED so that it can follow b_expr;
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* and for NULL so that it can follow b_expr in ColQualList without creating
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* postfix-operator problems.
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* To support target_el without AS, it used to be necessary to assign IDENT an
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* explicit precedence just less than Op. While that's not really necessary
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* since we removed postfix operators, it's still helpful to do so because
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* there are some other unreserved keywords that need precedence assignments.
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* If those keywords have the same precedence as IDENT then they clearly act
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* the same as non-keywords, reducing the risk of unwanted precedence effects.
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*
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* To support CUBE and ROLLUP in GROUP BY without reserving them, we give them
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* an explicit priority lower than '(', so that a rule with CUBE '(' will shift
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* rather than reducing a conflicting rule that takes CUBE as a function name.
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* Using the same precedence as IDENT seems right for the reasons given above.
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* We need to do this for PARTITION, RANGE, ROWS, and GROUPS to support
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* opt_existing_window_name (see comment there).
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*
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* The frame_bound productions UNBOUNDED PRECEDING and UNBOUNDED FOLLOWING
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* are even messier: since UNBOUNDED is an unreserved keyword (per spec!),
@@ -769,9 +762,14 @@ static Node *makeRecursiveViewSelect(char *relname, List *aliases, Node *query);
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* appear to cause UNBOUNDED to be treated differently from other unreserved
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* keywords anywhere else in the grammar, but it's definitely risky. We can
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* blame any funny behavior of UNBOUNDED on the SQL standard, though.
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*
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* To support CUBE and ROLLUP in GROUP BY without reserving them, we give them
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* an explicit priority lower than '(', so that a rule with CUBE '(' will shift
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* rather than reducing a conflicting rule that takes CUBE as a function name.
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* Using the same precedence as IDENT seems right for the reasons given above.
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*/
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%nonassocUNBOUNDED/* ideallyshould have same precedence as IDENT*/
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%nonassocIDENTGENERATEDNULL_PPARTITIONRANGEROWSGROUPSPRECEDINGFOLLOWINGCUBEROLLUP
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%nonassocUNBOUNDED/* ideallywould have same precedence as IDENT*/
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%nonassocIDENTPARTITIONRANGEROWSGROUPSPRECEDINGFOLLOWINGCUBEROLLUP
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%leftOpOPERATOR/* multi-character ops and user-defined operators*/
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%left'+''-'
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%left'*''/''%'
@@ -792,8 +790,6 @@ static Node *makeRecursiveViewSelect(char *relname, List *aliases, Node *query);
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* left-associativity among the JOIN rules themselves.
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*/
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%leftJOINCROSSLEFTFULLRIGHTINNER_PNATURAL
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/* kluge to keep xml_whitespace_option from causing shift/reduce conflicts*/
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%rightPRESERVESTRIP_P
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%%
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