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Commit32664b4

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Improve commentary about ArrayRef and ResTarget nodes.
1 parent3406901 commit32664b4

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2 files changed

+51
-18
lines changed

2 files changed

+51
-18
lines changed

‎src/include/nodes/parsenodes.h

Lines changed: 14 additions & 5 deletions
Original file line numberDiff line numberDiff line change
@@ -6,7 +6,7 @@
66
*
77
* Copyright (c) 1994, Regents of the University of California
88
*
9-
* $Id: parsenodes.h,v 1.76 1999/07/15 23:03:54 momjian Exp $
9+
* $Id: parsenodes.h,v 1.77 1999/07/1803:45:01 tgl Exp $
1010
*
1111
*-------------------------------------------------------------------------
1212
*/
@@ -810,14 +810,23 @@ typedef struct A_Indices
810810
/*
811811
* ResTarget -
812812
* result target (used in target list of pre-transformed Parse trees)
813+
*
814+
* In a SELECT or INSERT target list, 'name' is either NULL or
815+
* the column name assigned to the value. (If there is an 'AS ColumnLabel'
816+
* clause, the grammar sets 'name' from it; otherwise 'name' is initially NULL
817+
* and is filled in during the parse analysis phase.)
818+
* The 'indirection' field is not used at all.
819+
*
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* In an UPDATE target list, 'name' is the name of the destination column,
821+
* and 'indirection' stores any subscripts attached to the destination.
822+
* That is, our representation is UPDATE table SET name [indirection] = val.
813823
*/
814824
typedefstructResTarget
815825
{
816826
NodeTagtype;
817-
char*name;/* name of the result column */
818-
List*indirection;/* array references */
819-
Node*val;/* the value of the result (A_Expr or
820-
* Attr) (or A_Const) */
827+
char*name;/* column name or NULL */
828+
List*indirection;/* subscripts for destination column, or NIL */
829+
Node*val;/* the value expression to compute or assign */
821830
}ResTarget;
822831

823832
/*

‎src/include/nodes/primnodes.h

Lines changed: 37 additions & 13 deletions
Original file line numberDiff line numberDiff line change
@@ -6,7 +6,7 @@
66
*
77
* Copyright (c) 1994, Regents of the University of California
88
*
9-
* $Id: primnodes.h,v 1.31 1999/07/16 17:07:33 momjian Exp $
9+
* $Id: primnodes.h,v 1.32 1999/07/18 03:45:01 tgl Exp $
1010
*
1111
*-------------------------------------------------------------------------
1212
*/
@@ -302,13 +302,13 @@ typedef struct SubLink
302302

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/* ----------------
304304
* Array
305-
*arrayelemtype-basetype of the array's elements (homogenous!)
305+
*arrayelemtype- type of the array's elements (homogenous!)
306306
*arrayelemlength - length of that type
307-
*arrayelembyval-can you pass thiselementbyvalue?
307+
*arrayelembyval-is theelementtype pass-by-value?
308308
*arrayndim- number of dimensions of the array
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*arraylow- base for array indexing
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*arrayhigh- limit for array indexing
311-
*arraylen-
311+
*arraylen- total length of array object
312312
* ----------------
313313
*
314314
*memo from mao:the array support we inherited from 3.1 is just
@@ -328,15 +328,39 @@ typedef struct Array
328328
}Array;
329329

330330
/* ----------------
331-
*ArrayRef:
332-
*refelemtype- type of the element referenced here
333-
*refelemlength- length of that type
334-
*refelembyval- can you pass this element type by value?
335-
*refupperindexpr - expressions that evaluate to upper array index
336-
*reflowerexpr- the expressions that evaluate to a lower array index
337-
*refexpr- the expression that evaluates to an array
338-
*refassignexpr- the expression that evaluates to the new value
339-
*to be assigned to the array in case of replace.
331+
*ArrayRef: describes an array subscripting operation
332+
*
333+
* An ArrayRef can describe fetching a single element from an array,
334+
* fetching a subarray (array slice), storing a single element into
335+
* an array, or storing a slice. The "store" cases work with an
336+
* initial array value and a source value that is inserted into the
337+
* appropriate part of the array.
338+
*
339+
*refattrlength- total length of array object
340+
*refelemtype- type of the result of the subscript operation
341+
*refelemlength- length of the array element type
342+
*refelembyval- is the element type pass-by-value?
343+
*refupperindexpr - expressions that evaluate to upper array indexes
344+
*reflowerindexpr- expressions that evaluate to lower array indexes
345+
*refexpr- the expression that evaluates to an array value
346+
*refassgnexpr- expression for the source value, or NULL if fetch
347+
*
348+
* If reflowerindexpr = NIL, then we are fetching or storing a single array
349+
* element at the subscripts given by refupperindexpr. Otherwise we are
350+
* fetching or storing an array slice, that is a rectangular subarray
351+
* with lower and upper bounds given by the index expressions.
352+
* reflowerindexpr must be the same length as refupperindexpr when it
353+
* is not NIL.
354+
*
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* Note: array types can be fixed-length (refattrlength > 0), but only
356+
* when the element type is itself fixed-length. Otherwise they are
357+
* varlena structures and have refattrlength = -1. In any case,
358+
* an array type is never pass-by-value.
359+
*
360+
* Note: currently, refelemtype is NOT the element type, but the array type,
361+
* when doing subarray fetch or either type of store. It would be cleaner
362+
* to add more fields so we can distinguish the array element type from the
363+
* result type of the subscript operator...
340364
* ----------------
341365
*/
342366
typedefstructArrayRef

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