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Add further comments to window.c.

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FossilOrigin-Name: 900464567b2a5ce0c278a3297e4be1968f609258608aa0fbe2fc67709aa22a4b
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dan
2019-08-30 17:28:55 +00:00
parent ac6627327c
commit 1cac1766df
3 changed files with 85 additions and 26 deletions
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manifest
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@@ -1,5 +1,5 @@
C New\stest\scases\sfor\swindow\sfunctions\swith\sRANGE\sBETWEEN\sand\sDESC\sNULLS\sFIRST.
D 2019-08-30T16:46:12.848
C Add\sfurther\scomments\sto\swindow.c.
D 2019-08-30T17:28:55.760
F .fossil-settings/empty-dirs dbb81e8fc0401ac46a1491ab34a7f2c7c0452f2f06b54ebb845d024ca8283ef1
F .fossil-settings/ignore-glob 35175cdfcf539b2318cb04a9901442804be81cd677d8b889fcc9149c21f239ea
F LICENSE.md df5091916dbb40e6e9686186587125e1b2ff51f022cc334e886c19a0e9982724
@@ -613,7 +613,7 @@ F src/where.c fb546afbdbedc77a6193a236db92f6f85bc8e17412ec596230dd8aee03a93716
F src/whereInt.h 4a296fd4fa79fdcbc2b5e8c1b898901617655811223e1082b899c23ecb092217
F src/wherecode.c 535c8e228478fd971b9a5b6cb6773995b0fbf7020d5989508a5094ce5b8cd95b
F src/whereexpr.c 2757afbd5cfdbb420f9d0392e1bd5f5c0e33dee50a8c692befc7e502308e449f
F src/window.c 701bea99097fd9f2c49e0af54446c986853e639fa297248ea62fac5e3f3b8dba
F src/window.c ff37ca403ad3c47bb1e60b0e88c546aa5194524dc20d7f75e866187a093ae5d7
F test/8_3_names.test ebbb5cd36741350040fd28b432ceadf495be25b2
F test/affinity2.test b03930d288e38b07f55023a58538ad174605695e98934bdab1facf6bd9ecc436
F test/affinity3.test 6a101af2fc945ce2912f6fe54dd646018551710d
@@ -1838,7 +1838,7 @@ F vsixtest/vsixtest.tcl 6a9a6ab600c25a91a7acc6293828957a386a8a93
F vsixtest/vsixtest.vcxproj.data 2ed517e100c66dc455b492e1a33350c1b20fbcdc
F vsixtest/vsixtest.vcxproj.filters 37e51ffedcdb064aad6ff33b6148725226cd608e
F vsixtest/vsixtest_TemporaryKey.pfx e5b1b036facdb453873e7084e1cae9102ccc67a0
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U drh
Z 7f59914616f53a7b55c42685c9ae4ee5
P f7002f86c780e279c9f8a6268f317586519c059c9de2115ff6f1cad272570c29
R 717428315655334cbf16abae9c8648f7
U dan
Z e01e05b9266977bc594b107aacdc1011

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@@ -1 +1 @@
f7002f86c780e279c9f8a6268f317586519c059c9de2115ff6f1cad272570c29
900464567b2a5ce0c278a3297e4be1968f609258608aa0fbe2fc67709aa22a4b

87
src/window.c
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@@ -1499,19 +1499,78 @@ static void windowAggStep(
typedef struct WindowCodeArg WindowCodeArg;
typedef struct WindowCsrAndReg WindowCsrAndReg;
/*
** See comments above struct WindowCodeArg.
*/
struct WindowCsrAndReg {
int csr;
int reg;
int csr; /* Cursor number */
int reg; /* First in array of peer values */
};
/*
** A single instance of this structure is allocated on the stack by
** sqlite3WindowCodeStep() and a pointer to it passed to the various helper
** routines. This is to reduce the number of arguments required by each
** helper function.
**
** regArg:
** Each window function requires an accumulator register (just as an
** ordinary aggregate function does). This variable is set to the first
** in an array of accumulator registers - one for each window function
** in the WindowCodeArg.pMWin list.
**
** eDelete:
** The window functions implementation sometimes caches the input rows
** that it processes in a temporary table. If it is not zero, this
** variable indicates when rows may be removed from the temp table (in
** order to reduce memory requirements - it would always be safe just
** to leave them there). Possible values for eDelete are:
**
** WINDOW_RETURN_ROW:
** An input row can be discarded after it is returned to the caller.
**
** WINDOW_AGGINVERSE:
** An input row can be discarded after the window functions xInverse()
** callbacks have been invoked in it.
**
** WINDOW_AGGSTEP:
** An input row can be discarded after the window functions xStep()
** callbacks have been invoked in it.
**
** start,current,end
** Consider a window-frame similar to the following:
**
** (ORDER BY a, b GROUPS BETWEEN 2 PRECEDING AND 2 FOLLOWING)
**
** The windows functions implmentation caches the input rows in a temp
** table, sorted by "a, b" (it actually populates the cache lazily, and
** aggressively removes rows once they are no longer required, but that's
** a mere detail). It keeps three cursors open on the temp table. One
** (current) that points to the next row to return to the query engine
** once its window function values have been calculated. Another (end)
** points to the next row to call the xStep() method of each window function
** on (so that it is 2 groups ahead of current). And a third (start) that
** points to the next row to call the xInverse() method of each window
** function on.
**
** Each cursor (start, current and end) consists of a VDBE cursor
** (WindowCsrAndReg.csr) and an array of registers (starting at
** WindowCodeArg.reg) that always contains a copy of the peer values
** read from the corresponding cursor.
**
** Depending on the window-frame in question, all three cursors may not
** be required. In this case both WindowCodeArg.csr and reg are set to
** 0.
*/
struct WindowCodeArg {
Parse *pParse;
Window *pMWin;
Vdbe *pVdbe;
int regGosub;
int addrGosub;
int regArg;
int eDelete;
Parse *pParse; /* Parse context */
Window *pMWin; /* First in list of functions being processed */
Vdbe *pVdbe; /* VDBE object */
int addrGosub; /* OP_Gosub to this address to return one row */
int regGosub; /* Register used with OP_Gosub(addrGosub) */
int regArg; /* First in array of accumulator registers */
int eDelete; /* See above */
WindowCsrAndReg start;
WindowCsrAndReg current;
@@ -1880,14 +1939,14 @@ static void windowCodeRangeTest(
int csr1, /* Cursor number for cursor 1 */
int regVal, /* Register containing non-negative number */
int csr2, /* Cursor number for cursor 2 */
int lbl /* Jump destination if the condition is true */
int lbl /* Jump destination if condition is true */
){
Parse *pParse = p->pParse;
Vdbe *v = sqlite3GetVdbe(pParse);
ExprList *pOrderBy = p->pMWin->pOrderBy; /* ORDER BY clause for this window */
int reg1 = sqlite3GetTempReg(pParse); /* Register for csr1.peerVal+regVal */
int reg2 = sqlite3GetTempReg(pParse); /* Regiser for csr2.peerVal */
int regString = ++pParse->nMem; /* Register for constant value '' */
ExprList *pOrderBy = p->pMWin->pOrderBy; /* ORDER BY clause for window */
int reg1 = sqlite3GetTempReg(pParse); /* Reg. for csr1.peerVal+regVal */
int reg2 = sqlite3GetTempReg(pParse); /* Reg. for csr2.peerVal */
int regString = ++pParse->nMem; /* Reg. for constant value '' */
int arith = OP_Add; /* OP_Add or OP_Subtract */
int addrGe; /* Jump destination */