Fix a problem with the query optimizer for LIMIT/OFFSET queries when

underlying query is a UNION ALL and both arms of the UNION ALL are
subqueries with an ORDER BY clause.  This bug was reported at
[forum:/forumpost/6b5e9188f0657616|forum post 6b5e9188f0657616].  The
problem was introduced in 2015 (SQLite version 3.9.0) by check-in
[4b631364354068af].  See also ticket [b65cb2c8d91f6685].

FossilOrigin-Name: 6c806f64bbc9e98891bad0868575ee2ec5d0951ceb0c71d3ed417b45d5f27561

manifest

@@ -1,5 +1,5 @@
-C Fix\sa\stypo\son\sa\scomment\sused\sto\sgenerate\sbytecode\sdocumentation.
-D 2022-08-04T14:02:35.852
+C Fix\sa\sproblem\swith\sthe\squery\soptimizer\sfor\sLIMIT/OFFSET\squeries\swhen\nunderlying\squery\sis\sa\sUNION\sALL\sand\sboth\sarms\sof\sthe\sUNION\sALL\sare\nsubqueries\swith\san\sORDER\sBY\sclause.\s\sThis\sbug\swas\sreported\sat\n[forum:/forumpost/6b5e9188f0657616|forum\spost\s6b5e9188f0657616].\s\sThe\nproblem\swas\sintroduced\sin\s2015\s(SQLite\sversion\s3.9.0)\sby\scheck-in\n[4b631364354068af].\s\sSee\salso\sticket\s[b65cb2c8d91f6685].
+D 2022-08-04T17:15:00.492
 F .fossil-settings/empty-dirs dbb81e8fc0401ac46a1491ab34a7f2c7c0452f2f06b54ebb845d024ca8283ef1
 F .fossil-settings/ignore-glob 35175cdfcf539b2318cb04a9901442804be81cd677d8b889fcc9149c21f239ea
 F LICENSE.md df5091916dbb40e6e9686186587125e1b2ff51f022cc334e886c19a0e9982724
@@ -570,7 +570,7 @@ F src/printf.c e99ee9741e79ae3873458146f59644276657340385ade4e76a5f5d1c25793764
 F src/random.c 097dc8b31b8fba5a9aca1697aeb9fd82078ec91be734c16bffda620ced7ab83c
 F src/resolve.c efea4e5fbecfd6d0a9071b0be0d952620991673391b6ffaaf4c277b0bb674633
 F src/rowset.c ba9515a922af32abe1f7d39406b9d35730ed65efab9443dc5702693b60854c92
-F src/select.c 76708e3a8cb80f011f31f1eb6fa5f433aef8f47c85c0a2709148d673a719a846
+F src/select.c 4750fbe9d8ecb7236baf7a9bea4299bb87126e08c209645666a0ae8f0efbe0fc
 F src/shell.c.in 29749b34bbd19d0004fdb6f61f62659096e1c0b4dfb1ad2314e7fafbe9dd8d37
 F src/sqlite.h.in be265991edca9aea69986758b58ba81cbf5ae403fe0c4ea1d0c9df0cdc8f25ed
 F src/sqlite3.rc 5121c9e10c3964d5755191c80dd1180c122fc3a8
@@ -1286,7 +1286,7 @@ F test/null.test b7ff206a1c60fe01aa2abd33ef9ea83c93727d993ca8a613de86e925c9f2bc6
 F test/nulls1.test 7a5e4346ee4285034100b4cd20e6784f16a9d6c927e44ecdf10034086bbee9c9
 F test/numcast.test 5d126f7f581432e86a90d1e35cac625164aec4a1
 F test/numindex1.test 20a5450d4b056e48cd5db30e659f13347a099823
-F test/offset1.test f06b83657bcf26f9ce805e67450e189e282143b2
+F test/offset1.test 72cca52482cbd5bc687cfa67aa2566c859081b5a353fd2f9da9bbd3914dea1ef
 F test/openv2.test 0d3040974bf402e19b7df4b783e447289d7ab394
 F test/optfuzz-db01.c 9f2fa80b8f84ebbf1f2e8b13421a4e0477fe300f6686fbd76cac1d2db66e0fdc
 F test/optfuzz-db01.txt 21f6bdeadc701cf11528276e2a55c70bfcb846ba42df327f979bd9e7b6ce7041
@@ -1981,8 +1981,8 @@ F vsixtest/vsixtest.tcl 6a9a6ab600c25a91a7acc6293828957a386a8a93
 F vsixtest/vsixtest.vcxproj.data 2ed517e100c66dc455b492e1a33350c1b20fbcdc
 F vsixtest/vsixtest.vcxproj.filters 37e51ffedcdb064aad6ff33b6148725226cd608e
 F vsixtest/vsixtest_TemporaryKey.pfx e5b1b036facdb453873e7084e1cae9102ccc67a0
-P 597347d9c39f6ed068ac942a8c9853b1b745fce1eb5e9dd30f6c1cb312b36f53
-R ce5a27ffc72e7ec12d095a7689107487
+P 64348d0b665f61c3a89f51341f23ca87f939dd9e306dc58c2004e46ab04e696e
+R ee3ba899316d027809db4ccd10585a40
 U drh
-Z 549658791a10dec284226014b5aa7e75
+Z 55de9d5c0f343647378b885b0fe37df5
 # Remove this line to create a well-formed Fossil manifest.

manifest.uuid

@@ -1 +1 @@
-64348d0b665f61c3a89f51341f23ca87f939dd9e306dc58c2004e46ab04e696e
+6c806f64bbc9e98891bad0868575ee2ec5d0951ceb0c71d3ed417b45d5f27561

src/select.c

@@ -1688,7 +1688,7 @@ static void generateSortTail(
     if( addrOnce ) sqlite3VdbeJumpHere(v, addrOnce);
     addr = 1 + sqlite3VdbeAddOp2(v, OP_SorterSort, iTab, addrBreak);
     VdbeCoverage(v);
-    codeOffset(v, p->iOffset, addrContinue);
+    assert( p->iLimit==0 && p->iOffset==0 );
     sqlite3VdbeAddOp3(v, OP_SorterData, iTab, regSortOut, iSortTab);
     bSeq = 0;
   }else{
@@ -1696,6 +1696,9 @@ static void generateSortTail(
     codeOffset(v, p->iOffset, addrContinue);
     iSortTab = iTab;
     bSeq = 1;
+    if( p->iOffset>0 ){
+      sqlite3VdbeAddOp2(v, OP_AddImm, p->iLimit, -1);
+    }
   }
   for(i=0, iCol=nKey+bSeq-1; i<nColumn; i++){
 #ifdef SQLITE_ENABLE_SORTER_REFERENCES

test/offset1.test

@@ -156,6 +156,47 @@ do_execsql_test offset1-1.4.9 {
   LIMIT 9 OFFSET 1;
 } {2 b 3 c 4 d 5 e 6 w 7 x 8 y 9 z}
 
-
+# 2022-08-04
+# https://sqlite.org/forum/forumpost/6b5e9188f0657616
+#
+do_execsql_test offset1-2.0 {
+  CREATE TABLE employees (
+    id integer primary key,
+    name text,
+    city text,
+    department text,
+    salary integer
+  );
+  INSERT INTO employees VALUES
+    (11,'Diane','London','hr',70),
+    (12,'Bob','London','hr',78),
+    (21,'Emma','London','it',84),
+    (22,'Grace','Berlin','it',90),
+    (23,'Henry','London','it',104),
+    (24,'Irene','Berlin','it',104),
+    (25,'Frank','Berlin','it',120),
+    (31,'Cindy','Berlin','sales',96),
+    (32,'Dave','London','sales',96),
+    (33,'Alice','Berlin','sales',100);
+  CREATE VIEW v AS
+    SELECT * FROM (
+      SELECT * FROM employees 
+       WHERE salary < 100
+       ORDER BY salary desc)
+     UNION ALL 
+     SELECT * FROM (
+       SELECT * FROM employees
+       WHERE salary >= 100
+       ORDER BY salary asc);
+} {}
+do_execsql_test offset1-2.1 {
+  SELECT * FROM v LIMIT 5 OFFSET 2;
+} {
+  22  Grace  Berlin  it      90
+  21  Emma   London  it      84
+  12  Bob    London  hr      78
+  11  Diane  London  hr      70
+  33  Alice  Berlin  sales   100
+}
 
 finish_test