MXS-1829 Recognise PREVIOUS in addition to NEXT

Earlier only "SELECT NEXT VALUE FOR SEQ" was parsed
properly, while "SELECT PREVIOUS VALUE FOR SEQ" was not.
Now the latter statement is also parsed properly.

query_classifier/qc_sqlite/sqlite-src-3110100/src/parse.y

@@ -626,6 +626,7 @@ columnid(A) ::= nm(X). {
   NAMES NEXT
   NO
   OF OFFSET OPEN
+  PREVIOUS
   QUICK
   RAISE RECURSIVE /*REINDEX*/ RELEASE /*RENAME*/ /*REPLACE*/ RESTRICT ROLLBACK ROLLUP ROW
   SAVEPOINT SELECT_OPTIONS_KW /*SEQUENCE*/ SLAVE /*START*/ STATUS
@@ -1207,7 +1208,10 @@ selcollist(A) ::= sclp(P) nm(X) DOT STAR(Y). {
   A = sqlite3ExprListAppend(pParse,P, pDot);
 }
 %ifdef MAXSCALE
-selcollist(A) ::= sclp(P) NEXT VALUE FOR nm(X) as(Y).     {
+next_or_previous(A) ::= NEXT(X). {A = X;}
+next_or_previous(A) ::= PREVIOUS(X). {A = X;}
+
+selcollist(A) ::= sclp(P) next_or_previous VALUE FOR nm(X) as(Y).     {
   Expr* pSeq = sqlite3PExpr(pParse, TK_ID, 0, 0, &X);
   ExprList* pArgs = sqlite3ExprListAppend(pParse, NULL, pSeq);
   Token nextval = { "nextval", 7 };