database/sqlite
1
0
Fork 0
mirror of https://github.com/sqlite/sqlite.git synced 2025-11-11 01:42:22 +03:00
Code Activity

Add missing comment to new routine in select.c.

Browse Source 
FossilOrigin-Name: ef2f0cf21ba61bdd29e09cf41b012a2d757683f524a252f0af7dfee7df1a1a0f
This commit is contained in:
dan
2021-03-09 16:47:33 +00:00
parent 4fcb30b7d7
commit 96ecb7b004
3 changed files with 37 additions and 39 deletions
Download Patch File Download Diff File Expand all files Collapse all files

59
src/select.c
View File

@@ -740,37 +740,38 @@ static void codeOffset(
}
}
#if 0
/*
** Add code that will check to make sure the N registers starting at iMem
** form a distinct entry. iTab is a sorting index that holds previously
** seen combinations of the N values. A new entry is made in iTab
** if the current N values are new.
** Add code that will check to make sure the array of registers starting at
** iMem form a distinct entry. This is used by both "SELECT DISTINCT ..." and
** distinct aggregates ("SELECT count(DISTINCT <expr>) ..."). Parameter iTab is
** the cursor number of an ephemeral table opened by instruction iTabAddr for
** the code generated by this routine to use. There are three strategies, based
** on the value of parameter eTnctType:
**
** A jump to addrRepeat is made and the N+1 values are popped from the
** stack if the top N elements are not distinct.
** WHERE_DISTINCT_UNORDERED/WHERE_DISTINCT_NOOP:
** The ephemeral cursor table is queries for a record identical to the
** record formed by the current array of registers. If one is found,
** jump to VM address addrRepeat. Otherwise, insert a new record into
** the ephemeral cursor and proceed.
**
** WHERE_DISTINCT_ORDERED:
** In this case rows are being delivered sorted order sorted. The ephermal
** table is not required in this case. Instead, the current set of
** registers are compared to previous row. If they match, the new row
** is not distinct and control jumps to VM address addrRepeat. Otherwise,
** the VM program proceeds with processing the new row.
**
** WHERE_DISTINCT_UNIQUE:
** In this case it has already been determined that the rows are distinct.
** No special action is required.
**
** Parameter pEList is the list of expressions used to generated the
** contents of each row. It is used by this routine to determine (a)
** how many elements there are in the array of registers and (b) the
** collation sequences that should be used for the comparisons if
** eTnctType is WHERE_DISTINCT_ORDERED.
*/
static void codeDistinct(
Parse *pParse, /* Parsing and code generating context */
int iTab, /* A sorting index used to test for distinctness */
int addrRepeat, /* Jump to here if not distinct */
int N, /* Number of elements */
int iMem /* First element */
){
Vdbe *v;
int r1;
v = pParse->pVdbe;
r1 = sqlite3GetTempReg(pParse);
sqlite3VdbeAddOp4Int(v, OP_Found, iTab, addrRepeat, iMem, N); VdbeCoverage(v);
sqlite3VdbeAddOp3(v, OP_MakeRecord, iMem, N, r1);
sqlite3VdbeAddOp4Int(v, OP_IdxInsert, iTab, r1, iMem, N);
sqlite3VdbeChangeP5(v, OPFLAG_USESEEKRESULT);
sqlite3ReleaseTempReg(pParse, r1);
}
#endif
static void codeDistinct2(
Parse *pParse, /* Parsing and code generating context */
int eTnctType, /* WHERE_DISTINCT_* value */
int iTab, /* A sorting index used to test for distinctness */
@@ -1087,7 +1088,7 @@ static void selectInnerLoop(
*/
if( hasDistinct ){
assert( nResultCol==p->pEList->nExpr );
codeDistinct2(pParse, pDistinct->eTnctType, pDistinct->tabTnct,
codeDistinct(pParse, pDistinct->eTnctType, pDistinct->tabTnct,
pDistinct->addrTnct, iContinue, p->pEList, regResult);
if( pSort==0 ){
codeOffset(v, p->iOffset, iContinue);
@@ -5748,7 +5749,7 @@ static void updateAccumulator(
}
testcase( nArg==0 ); /* Error condition */
testcase( nArg>1 ); /* Also an error */
codeDistinct2(pParse, eDistinctType, pF->iDistinct, pF->iDistAddr,
codeDistinct(pParse, eDistinctType, pF->iDistinct, pF->iDistAddr,
addrNext, pList, regAgg);
}
if( pF->pFunc->funcFlags & SQLITE_FUNC_NEEDCOLL ){