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Avoid redundant ORDER BY operations when rewriting SELECT statements that

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contain window functions.

FossilOrigin-Name: 336de43a47e206fe7629072e5b8c80d4ede17ead8ef4dcf5d8da6833ff22d2f9
This commit is contained in:
dan
2018-06-27 19:48:50 +00:00
parent c994b0225b
commit f02cdd379a
4 changed files with 27 additions and 19 deletions
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26
src/window.c
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@@ -721,6 +721,18 @@ int sqlite3WindowRewrite(Parse *pParse, Select *p){
p->pGroupBy = 0;
p->pHaving = 0;
/* Create the ORDER BY clause for the sub-select. This is the concatenation
** of the window PARTITION and ORDER BY clauses. Then, if this makes it
** redundant, remove the ORDER BY from the parent SELECT. */
pSort = sqlite3ExprListDup(db, pMWin->pPartition, 0);
pSort = exprListAppendList(pParse, pSort, pMWin->pOrderBy);
if( pSort && p->pOrderBy ){
if( sqlite3ExprListCompare(pSort, p->pOrderBy, -1)==0 ){
sqlite3ExprListDelete(db, p->pOrderBy);
p->pOrderBy = 0;
}
}
/* Assign a cursor number for the ephemeral table used to buffer rows.
** The OpenEphemeral instruction is coded later, after it is known how
** many columns the table will have. */
@@ -730,15 +742,11 @@ int sqlite3WindowRewrite(Parse *pParse, Select *p){
selectWindowRewriteEList(pParse, pMWin, p->pOrderBy, &pSublist);
pMWin->nBufferCol = (pSublist ? pSublist->nExpr : 0);
/* Create the ORDER BY clause for the sub-select. This is the concatenation
** of the window PARTITION and ORDER BY clauses. Append the same
** expressions to the sub-select expression list. They are required to
** figure out where boundaries for partitions and sets of peer rows. */
pSort = sqlite3ExprListDup(db, pMWin->pPartition, 0);
if( pMWin->pOrderBy ){
pSort = exprListAppendList(pParse, pSort, pMWin->pOrderBy);
}
pSublist = exprListAppendList(pParse, pSublist, pSort);
/* Append the PARTITION BY and ORDER BY expressions to the to the
** sub-select expression list. They are required to figure out where
** boundaries for partitions and sets of peer rows lie. */
pSublist = exprListAppendList(pParse, pSublist, pMWin->pPartition);
pSublist = exprListAppendList(pParse, pSublist, pMWin->pOrderBy);
/* Append the arguments passed to each window function to the
** sub-select expression list. Also allocate two registers for each