database/sqlite
1
0
Fork 0
mirror of https://github.com/sqlite/sqlite.git synced 2025-11-14 00:22:38 +03:00
Code Activity

Remove an unnecessary OP_Null in the IN-operator logic. Attempt to clarify

Browse Source 
comments explaining the IN-operator code, though it is not clear that the
comments are correct even yet - more work to be done.

FossilOrigin-Name: c11e55fabbc718cb324ecd3540453c25db98f50c
This commit is contained in:
drh
2014-08-01 18:00:24 +00:00
parent 5c3e9cf9de
commit e21a6e1dfe
4 changed files with 33 additions and 30 deletions
Download Patch File Download Diff File Expand all files Collapse all files

42
src/expr.c
View File

@@ -1525,29 +1525,34 @@ int sqlite3CodeOnce(Parse *pParse){
**
** When the b-tree is being used for membership tests, the calling function
** might need to know whether or not the RHS side of the IN operator
** contains a NULL. If prNotFound is not NULL and
** contains a NULL. If prRhsHasNull is not a NULL pointer and
** if there is any chance that the (...) might contain a NULL value at
** runtime, then a register is allocated and the register number written
** to *prNotFound. If there is no chance that the (...) contains a
** NULL value, then *prNotFound is left unchanged.
** to *prRhsHasNull. If there is no chance that the (...) contains a
** NULL value, then *prRhsHasNull is left unchanged.
**
** If a register is allocated and its location stored in *prNotFound, then
** its initial value is NULL. If the (...) does not remain constant
** for the duration of the query (i.e. the SELECT within the (...)
** is a correlated subquery) then the value of the allocated register is
** reset to NULL each time the subquery is rerun. This allows the
** caller to use vdbe code equivalent to the following:
** If a register is allocated and its location stored in *prRhsHasNull, then
** the value in that register will be:
**
** if( register==NULL ){
** has_null = <test if data structure contains null>
** register = 1
** 0 if the (...) contains no NULL values
** 1 if the (...) does not contain NULL values
** NULL if we do not yet know if (...) contains NULLs
**
** If the (...) does not remain constant for the duration of the query
** (i.e. the SELECT within the (...) is a correlated subquery) then the
** value of the allocated register is reset to NULL each time the subquery
** is rerun. This allows the caller to use vdbe code equivalent to the
** following:
**
** if( r[*prRhsHasNull] IS NULL ){
** r[*prRhsHasNull] = <test if data structure contains null>
** }
**
** in order to avoid running the <test if data structure contains null>
** test more often than is necessary.
*/
#ifndef SQLITE_OMIT_SUBQUERY
int sqlite3FindInIndex(Parse *pParse, Expr *pX, u32 inFlags, int *prNotFound){
int sqlite3FindInIndex(Parse *pParse, Expr *pX, u32 inFlags, int *prRhsHasNull){
Select *p; /* SELECT to the right of IN operator */
int eType = 0; /* Type of RHS table. IN_INDEX_* */
int iTab = pParse->nTab++; /* Cursor of the RHS table */
@@ -1621,9 +1626,9 @@ int sqlite3FindInIndex(Parse *pParse, Expr *pX, u32 inFlags, int *prNotFound){
assert( IN_INDEX_INDEX_DESC == IN_INDEX_INDEX_ASC+1 );
eType = IN_INDEX_INDEX_ASC + pIdx->aSortOrder[0];
if( prNotFound && !pTab->aCol[iCol].notNull ){
*prNotFound = ++pParse->nMem;
sqlite3VdbeAddOp2(v, OP_Null, 0, *prNotFound);
if( prRhsHasNull && !pTab->aCol[iCol].notNull ){
*prRhsHasNull = ++pParse->nMem;
sqlite3VdbeAddOp2(v, OP_Null, 0, *prRhsHasNull);
}
sqlite3VdbeJumpHere(v, iAddr);
}
@@ -1643,9 +1648,8 @@ int sqlite3FindInIndex(Parse *pParse, Expr *pX, u32 inFlags, int *prNotFound){
if( pX->pLeft->iColumn<0 && !ExprHasProperty(pX, EP_xIsSelect) ){
eType = IN_INDEX_ROWID;
}
}else if( prNotFound ){
*prNotFound = rMayHaveNull = ++pParse->nMem;
sqlite3VdbeAddOp2(v, OP_Null, 0, rMayHaveNull);
}else if( prRhsHasNull ){
*prRhsHasNull = rMayHaveNull = ++pParse->nMem;
}
sqlite3CodeSubselect(pParse, pX, rMayHaveNull, eType==IN_INDEX_ROWID);
pParse->nQueryLoop = savedNQueryLoop;