Is the query flattener restriction 29 (do not allow both EP_InnerON and

EP_OuterON constraints on the same FROM clause term) really necessary?   This
branch explores what happens if we omit that restriction.  This is an effort
to address the performance regression reported by
[forum:/forumpost/96b9e5709cf47cda|forum post 96b9e5709cf47cda] that is caused
by flattener restriction 29.

FossilOrigin-Name: 19270577ad1d08c9e6e5f0600396b8a1ccda9df1e67a0df845aee6b60437f379

manifest

@@ -1,5 +1,5 @@
-C Clarify\scomments\sthat\sdescribe\squery\sflattener\srestrictions\sassociated\swith\nouter\sjoins.\s\sNo\scode\schanges.
-D 2022-09-19T19:25:15.448
+C Is\sthe\squery\sflattener\srestriction\s29\s(do\snot\sallow\sboth\sEP_InnerON\sand\nEP_OuterON\sconstraints\son\sthe\ssame\sFROM\sclause\sterm)\sreally\snecessary?\s\s\sThis\nbranch\sexplores\swhat\shappens\sif\swe\somit\sthat\srestriction.\s\sThis\sis\san\seffort\nto\saddress\sthe\sperformance\sregression\sreported\sby\n[forum:/forumpost/96b9e5709cf47cda|forum\spost\s96b9e5709cf47cda]\sthat\sis\scaused\nby\sflattener\srestriction\s29.
+D 2022-09-20T16:57:49.607
 F .fossil-settings/empty-dirs dbb81e8fc0401ac46a1491ab34a7f2c7c0452f2f06b54ebb845d024ca8283ef1
 F .fossil-settings/ignore-glob 35175cdfcf539b2318cb04a9901442804be81cd677d8b889fcc9149c21f239ea
 F LICENSE.md df5091916dbb40e6e9686186587125e1b2ff51f022cc334e886c19a0e9982724
@@ -539,7 +539,7 @@ F src/date.c 94ce83b4cd848a387680a5f920c9018c16655db778c4d36525af0a0f34679ac5
 F src/dbpage.c 5808e91bc27fa3981b028000f8fadfdc10ce9e59a34ce7dc4e035a69be3906ec
 F src/dbstat.c 861e08690fcb0f2ee1165eff0060ea8d4f3e2ea10f80dab7d32ad70443a6ff2d
 F src/delete.c 86573edae75e3d3e9a8b590d87db8e47222103029df4f3e11fa56044459b514e
-F src/expr.c 24e828db6b2fab8aabfb5d2c0d83dbdfc5a1972b1147fa893350e317ab7e282f
+F src/expr.c a6692ca00680c8ac4ec6cf637e04df1ca331e1a68e311b425eea61f0c8477019
 F src/fault.c 460f3e55994363812d9d60844b2a6de88826e007
 F src/fkey.c 722f20779f5342a787922deded3628d8c74b5249cab04098cf17ee2f2aaff002
 F src/func.c 8f72e88cccdee22185133c10f96ccd61dc34c5ea4b1fa9a73c237ef59b2e64f1
@@ -588,7 +588,7 @@ F src/printf.c e99ee9741e79ae3873458146f59644276657340385ade4e76a5f5d1c25793764
 F src/random.c 546d6feb15ec69c1aafe9bb351a277cbb498fd5410e646add673acb805714960
 F src/resolve.c efea4e5fbecfd6d0a9071b0be0d952620991673391b6ffaaf4c277b0bb674633
 F src/rowset.c ba9515a922af32abe1f7d39406b9d35730ed65efab9443dc5702693b60854c92
-F src/select.c dcfd2df77e4601555cef48174e3c61723f72fccfdd5b80caa5da63e23338c040
+F src/select.c 57813f5b8d716d69f3375053022d45150b7bb913bde8eac9cd6e64a519c13f8a
 F src/shell.c.in e7e7c2c69ae86c5ee9e8ad66227203d46ff6dce8700a1b1dababff01c71d33df
 F src/sqlite.h.in b9b7fd73239d94db20332bb6e504688001e5564b655e1318a4427a1caef4b99e
 F src/sqlite3.rc 5121c9e10c3964d5755191c80dd1180c122fc3a8
@@ -2000,8 +2000,11 @@ F vsixtest/vsixtest.tcl 6a9a6ab600c25a91a7acc6293828957a386a8a93
 F vsixtest/vsixtest.vcxproj.data 2ed517e100c66dc455b492e1a33350c1b20fbcdc
 F vsixtest/vsixtest.vcxproj.filters 37e51ffedcdb064aad6ff33b6148725226cd608e
 F vsixtest/vsixtest_TemporaryKey.pfx e5b1b036facdb453873e7084e1cae9102ccc67a0
-P 8032db4ade66f70a102abb9d3a49e20620e204c45ad7a954a49d20403985bf07
-R 279e5ed5d3d08518a51dc0906b1aae25
+P 2647d73bb1876d01851f52cb3fd6af08a962ab336b6d51c160d27b1baf94f75f
+R 60a74f8c958f8f5c6d2d000c0573265e
+T *branch * flattener-omit-restriction-29
+T *sym-flattener-omit-restriction-29 *
+T -sym-trunk *
 U drh
-Z 9a3376787d630872f605d6b2d292568c
+Z a7b69d349e01c35beb24d52a569b48a5
 # Remove this line to create a well-formed Fossil manifest.

manifest.uuid

@@ -1 +1 @@
-2647d73bb1876d01851f52cb3fd6af08a962ab336b6d51c160d27b1baf94f75f
+19270577ad1d08c9e6e5f0600396b8a1ccda9df1e67a0df845aee6b60437f379

src/expr.c

@@ -3223,6 +3223,7 @@ void sqlite3CodeRhsOfIN(
     sqlite3VdbeChangeP4(v, addr, (void *)pKeyInfo, P4_KEYINFO);
   }
   if( addrOnce ){
+    sqlite3VdbeAddOp2(v, OP_Rewind, iTab, sqlite3VdbeCurrentAddr(v)+1);
     sqlite3VdbeJumpHere(v, addrOnce);
     /* Subroutine return */
     assert( ExprUseYSub(pExpr) );

src/select.c

@@ -3724,7 +3724,7 @@ static int multiSelectOrderBy(
 ** the left operands of a RIGHT JOIN.  In either case, we need to potentially
 ** bypass the substituted expression with OP_IfNullRow.
 **
-** Suppose the original expression integer constant.  Even though the table
+** Suppose the original expression is an integer constant. Even though the table
 ** has the nullRow flag set, because the expression is an integer constant,
 ** it will not be NULLed out.  So instead, we insert an OP_IfNullRow opcode
 ** that checks to see if the nullRow flag is set on the table.  If the nullRow
@@ -4296,15 +4296,6 @@ static int flattenSubquery(
     }
     isOuterJoin = 1;
   }
-#ifdef SQLITE_EXTRA_IFNULLROW
-  else if( iFrom>0 && !isAgg ){
-    /* Setting isOuterJoin to -1 causes OP_IfNullRow opcodes to be generated for
-    ** every reference to any result column from subquery in a join, even
-    ** though they are not necessary.  This will stress-test the OP_IfNullRow 
-    ** opcode. */
-    isOuterJoin = -1;
-  }
-#endif
 
   assert( pSubSrc->nSrc>0 );  /* True by restriction (7) */
   if( iFrom>0 && (pSubSrc->a[0].fg.jointype & JT_LTORJ)!=0 ){
@@ -4314,6 +4305,7 @@ static int flattenSubquery(
     return 0;       /* (28) */
   }
 
+#if 0  /* NO LONGER REQUIRED */
   /* Restriction (29): 
   **
   ** We do not want two constraints on the same FROM-clause term of the
@@ -4340,6 +4332,7 @@ static int flattenSubquery(
       return 0;
     }
   }
+#endif /* NO LONGER REQUIRED */
 
   /* Restriction (17): If the sub-query is a compound SELECT, then it must
   ** use only the UNION ALL operator. And none of the simple select queries