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Remove an optimization that can no longer occur, being superceded by the

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subquery-reuse optimization.  Put an assert in place of the optimization
to detect if the need for this optimization ever returns.

FossilOrigin-Name: 4fcdc7a2939457e51aab37cab168677cd7f464a9a0aff4f8981e864a30828b3b
This commit is contained in:
drh
2018-12-31 20:13:12 +00:00
parent 0de6efe59e
commit d471bcb396
3 changed files with 13 additions and 23 deletions
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22
src/select.c
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@@ -5835,22 +5835,12 @@ int sqlite3Select(
pSub = pItem->pSelect;
if( pSub==0 ) continue;
/* Sometimes the code for a subquery will be generated more than
** once, if the subquery is part of the WHERE clause in a LEFT JOIN,
** for example. In that case, do not regenerate the code to manifest
** a view or the co-routine to implement a view. The first instance
** is sufficient, though the subroutine to manifest the view does need
** to be invoked again. */
if( pItem->addrFillSub ){
if( pItem->fg.viaCoroutine==0 ){
/* The subroutine that manifests the view might be a one-time routine,
** or it might need to be rerun on each iteration because it
** encodes a correlated subquery. */
testcase( sqlite3VdbeGetOp(v, pItem->addrFillSub)->opcode==OP_Once );
sqlite3VdbeAddOp2(v, OP_Gosub, pItem->regReturn, pItem->addrFillSub);
}
continue;
}
/* The code for a subquery should only be generated once, though it is
** technically harmless for it to be generated multiple times. The
** following assert() will detect if something changes to cause
** the same subquery to be coded multiple times, as a signal to the
** developers to try to optimize the situation. */
assert( pItem->addrFillSub==0 );
/* Increment Parse.nHeight by the height of the largest expression
** tree referred to by this, the parent select. The child select