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Improve comments and code legibility in new file window.c.

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FossilOrigin-Name: bb915854d435bdd78f141d70e23527e97922ec176acd3ed8060c78dffc96bab8
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dan
2018-06-14 14:27:05 +00:00
parent 13078caac4
commit 54a9ab3f13
3 changed files with 127 additions and 33 deletions
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146
src/window.c
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@@ -1236,6 +1236,12 @@ static void windowReturnRows(
sqlite3VdbeJumpHere(v, addr+1); /* The OP_Goto */
}
/*
** Generate code to set the accumulator register for each window function
** in the linked list passed as the second argument to NULL. And perform
** any equivalent initialization required by any built-in window functions
** in the list.
*/
static int windowInitAccum(Parse *pParse, Window *pMWin){
Vdbe *v = sqlite3GetVdbe(pParse);
int regArg;
@@ -1258,15 +1264,11 @@ static int windowInitAccum(Parse *pParse, Window *pMWin){
/*
** This function does the work of sqlite3WindowCodeStep() for all "ROWS"
** window frame types except for "BETWEEN UNBOUNDED PRECEDING AND CURRENT
** ROW". Pseudo-code for each follows.
**
** ROWS BETWEEN <expr1> PRECEDING AND <expr2> FOLLOWING
** ----------------------------------------------------
**
** Pseudo-code for the implementation of this window frame type is as
** follows. sqlite3WhereBegin() has already been called to generate the
** top of the main loop when this function is called.
**
** Each time the sub-routine at addrGosub is invoked, a single output
** row is generated based on the current row indicated by Window.iEphCsr.
**
** ...
** if( new partition ){
@@ -1551,6 +1553,16 @@ static void windowCodeRowExprStep(
}
/*
** This function does the work of sqlite3WindowCodeStep() for cases that
** would normally be handled by windowCodeDefaultStep() when there are
** one or more built-in window-functions that require the entire partition
** to be cached in a temp table before any rows can be returned. Additionally.
** "RANGE BETWEEN CURRENT ROW AND UNBOUNDED FOLLOWING" is always handled by
** this function.
**
** Pseudo-code corresponding to the VM code generated by this function
** for each type of window follows.
**
** RANGE BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW
**
** flush_partition:
@@ -1581,8 +1593,64 @@ static void windowCodeRowExprStep(
** Return
**
** ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW
** RANGE BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING
**
** As above, except that the "if( new peer )" branch is always taken.
**
** RANGE BETWEEN CURRENT ROW AND CURRENT ROW
**
** As above, except that each of the for() loops becomes:
**
** for(i=0; i<ctr; i++){
** Gosub addrGosub
** AggStep (xInverse, iEphCsr)
** Next iEphCsr
** }
**
** RANGE BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING
**
** flush_partition:
** Once {
** OpenDup (iEphCsr -> csrLead)
** }
** foreach row (csrLead) {
** AggStep (csrLead)
** }
** foreach row (iEphCsr) {
** Gosub addrGosub
** }
**
** RANGE BETWEEN CURRENT ROW AND UNBOUNDED FOLLOWING
**
** flush_partition:
** Once {
** OpenDup (iEphCsr -> csrLead)
** }
** foreach row (csrLead){
** AggStep (csrLead)
** }
** Rewind (csrLead)
** Integer ctr 0
** foreach row (csrLead){
** if( new peer ){
** AggFinal (xValue)
** for(i=0; i<ctr; i++){
** Gosub addrGosub
** AggStep (xInverse, iEphCsr)
** Next iEphCsr
** }
** Integer ctr 0
** }
** Incr ctr
** }
**
** AggFinal (xFinalize)
** for(i=0; i<ctr; i++){
** Gosub addrGosub
** Next iEphCsr
** }
**
** ResetSorter (csr)
** Return
*/
static void windowCodeCacheStep(
Parse *pParse,
@@ -1598,7 +1666,7 @@ static void windowCodeCacheStep(
int addr;
ExprList *pPart = pMWin->pPartition;
ExprList *pOrderBy = pMWin->pOrderBy;
int nPeer = pOrderBy->nExpr;
int nPeer = pOrderBy ? pOrderBy->nExpr : 0;
int regNewPeer;
int addrGoto; /* Address of Goto used to jump flush_par.. */
@@ -1610,8 +1678,9 @@ static void windowCodeCacheStep(
int regArg; /* Register array to martial function args */
int regSize;
int nArg;
int bReverse;
int lblEmpty;
int bReverse = pMWin->pOrderBy && pMWin->eStart==TK_CURRENT
&& pMWin->eEnd==TK_UNBOUNDED;
assert( (pMWin->eStart==TK_UNBOUNDED && pMWin->eEnd==TK_CURRENT)
|| (pMWin->eStart==TK_UNBOUNDED && pMWin->eEnd==TK_UNBOUNDED)
@@ -1620,7 +1689,6 @@ static void windowCodeCacheStep(
);
lblEmpty = sqlite3VdbeMakeLabel(v);
bReverse = (pMWin->eStart==TK_CURRENT && pMWin->eEnd==TK_UNBOUNDED);
regNewPeer = pParse->nMem+1;
pParse->nMem += nPeer;
@@ -1878,34 +1946,60 @@ void sqlite3WindowCodeStep(
int addrGosub /* OP_Gosub here to return each row */
){
Window *pMWin = p->pWin;
ExprList *pOrderBy = pMWin->pOrderBy;
/* Call windowCodeRowExprStep() for all "ROWS" window modes except:
/* There are three different functions that may be used to do the work
** of this one, depending on the window frame and the specific built-in
** window functions used (if any).
**
** windowCodeRowExprStep() handles all "ROWS" window frames, except for:
**
** ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW
**
** The exception is because windowCodeRowExprStep() implements all window
** frame types by caching the entire partition in a temp table, and
** "ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW" is easy enough to
** implement without such a cache.
**
** windowCodeCacheStep() is used for:
**
** RANGE BETWEEN CURRENT ROW AND UNBOUNDED FOLLOWING
**
** It is also used for anything not handled by windowCodeRowExprStep()
** that invokes a built-in window function that requires the entire
** partition to be cached in a temp table before any rows are returned
** (e.g. nth_value() or percent_rank()).
**
** Finally, assuming there is no built-in window function that requires
** the partition to be cached, windowCodeDefaultStep() is used for:
**
** RANGE BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW
** RANGE BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING
** RANGE BETWEEN CURRENT ROW AND CURRENT ROW
** ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW
**
** windowCodeDefaultStep() is the only one of the three functions that
** does not cache each partition in a temp table before beginning to
** return rows.
*/
if( (pMWin->eType==TK_ROWS
&& (pMWin->eStart!=TK_UNBOUNDED || pMWin->eEnd!=TK_CURRENT || !pOrderBy))
if( pMWin->eType==TK_ROWS
&& (pMWin->eStart!=TK_UNBOUNDED||pMWin->eEnd!=TK_CURRENT||!pMWin->pOrderBy)
){
windowCodeRowExprStep(pParse, p, pWInfo, regGosub, addrGosub);
}else{
Window *pWin;
int bCache = 0;
int bCache = 0; /* True to use CacheStep() */
if( pMWin->eStart==TK_CURRENT && pMWin->eEnd==TK_UNBOUNDED && pOrderBy ){
if( pMWin->eStart==TK_CURRENT && pMWin->eEnd==TK_UNBOUNDED ){
bCache = 1;
}else{
/* Call windowCodeCacheStep() if there is a window function that requires
** that the entire partition be cached in a temp table before any rows
** are returned. */
for(pWin=pMWin; pWin; pWin=pWin->pNextWin){
FuncDef *pFunc = pWin->pFunc;
if( (pFunc->funcFlags & SQLITE_FUNC_WINDOW_SIZE)
|| (pFunc->xSFunc==nth_valueStepFunc)
|| (pFunc->xSFunc==first_valueStepFunc)
|| (pFunc->xSFunc==leadStepFunc)
|| (pFunc->xSFunc==lagStepFunc)
){
|| (pFunc->xSFunc==nth_valueStepFunc)
|| (pFunc->xSFunc==first_valueStepFunc)
|| (pFunc->xSFunc==leadStepFunc)
|| (pFunc->xSFunc==lagStepFunc)
){
bCache = 1;
break;
}