Support FETCH FIRST WITH TIES

WITH TIES is an option to the FETCH FIRST N ROWS clause (the SQL
standard's spelling of LIMIT), where you additionally get rows that
compare equal to the last of those N rows by the columns in the
mandatory ORDER BY clause.

There was a proposal by Andrew Gierth to implement this functionality in
a more powerful way that would yield more features, but the other patch
had not been finished at this time, so we decided to use this one for
now in the spirit of incremental development.

Author: Surafel Temesgen <surafel3000@gmail.com>
Reviewed-by: Álvaro Herrera <alvherre@alvh.no-ip.org>
Reviewed-by: Tomas Vondra <tomas.vondra@2ndquadrant.com>
Discussion: https://postgr.es/m/CALAY4q9ky7rD_A4vf=FVQvCGngm3LOes-ky0J6euMrg=_Se+ag@mail.gmail.com
Discussion: https://postgr.es/m/87o8wvz253.fsf@news-spur.riddles.org.uk

4 files changed, 22 insertions, 0 deletions

diff --git a/src/backend/nodes/copyfuncs.c b/src/backend/nodes/copyfuncs.c
index f9d86859ee7..1525c0de725 100644
--- a/src/backend/nodes/copyfuncs.c
+++ b/src/backend/nodes/copyfuncs.c
@@ -1185,6 +1185,11 @@ _copyLimit(const Limit *from)
 	 */
 	COPY_NODE_FIELD(limitOffset);
 	COPY_NODE_FIELD(limitCount);
+	COPY_SCALAR_FIELD(limitOption);
+	COPY_SCALAR_FIELD(uniqNumCols);
+	COPY_POINTER_FIELD(uniqColIdx, from->uniqNumCols * sizeof(AttrNumber));
+	COPY_POINTER_FIELD(uniqOperators, from->uniqNumCols * sizeof(Oid));
+	COPY_POINTER_FIELD(uniqCollations, from->uniqNumCols * sizeof(Oid));
 
 	return newnode;
 }
@@ -3079,6 +3084,7 @@ _copyQuery(const Query *from)
 	COPY_NODE_FIELD(sortClause);
 	COPY_NODE_FIELD(limitOffset);
 	COPY_NODE_FIELD(limitCount);
+	COPY_SCALAR_FIELD(limitOption);
 	COPY_NODE_FIELD(rowMarks);
 	COPY_NODE_FIELD(setOperations);
 	COPY_NODE_FIELD(constraintDeps);
@@ -3163,6 +3169,7 @@ _copySelectStmt(const SelectStmt *from)
 	COPY_NODE_FIELD(sortClause);
 	COPY_NODE_FIELD(limitOffset);
 	COPY_NODE_FIELD(limitCount);
+	COPY_SCALAR_FIELD(limitOption);
 	COPY_NODE_FIELD(lockingClause);
 	COPY_NODE_FIELD(withClause);
 	COPY_SCALAR_FIELD(op);
diff --git a/src/backend/nodes/equalfuncs.c b/src/backend/nodes/equalfuncs.c
index e8e781834a5..4f34189ab5c 100644
--- a/src/backend/nodes/equalfuncs.c
+++ b/src/backend/nodes/equalfuncs.c
@@ -981,6 +981,7 @@ _equalQuery(const Query *a, const Query *b)
 	COMPARE_NODE_FIELD(sortClause);
 	COMPARE_NODE_FIELD(limitOffset);
 	COMPARE_NODE_FIELD(limitCount);
+	COMPARE_SCALAR_FIELD(limitOption);
 	COMPARE_NODE_FIELD(rowMarks);
 	COMPARE_NODE_FIELD(setOperations);
 	COMPARE_NODE_FIELD(constraintDeps);
@@ -1055,6 +1056,7 @@ _equalSelectStmt(const SelectStmt *a, const SelectStmt *b)
 	COMPARE_NODE_FIELD(sortClause);
 	COMPARE_NODE_FIELD(limitOffset);
 	COMPARE_NODE_FIELD(limitCount);
+	COMPARE_SCALAR_FIELD(limitOption);
 	COMPARE_NODE_FIELD(lockingClause);
 	COMPARE_NODE_FIELD(withClause);
 	COMPARE_SCALAR_FIELD(op);
diff --git a/src/backend/nodes/outfuncs.c b/src/backend/nodes/outfuncs.c
index 35ed8c0d538..5b826509ebe 100644
--- a/src/backend/nodes/outfuncs.c
+++ b/src/backend/nodes/outfuncs.c
@@ -931,6 +931,11 @@ _outLimit(StringInfo str, const Limit *node)
 
 	WRITE_NODE_FIELD(limitOffset);
 	WRITE_NODE_FIELD(limitCount);
+	WRITE_ENUM_FIELD(limitOption, LimitOption);
+	WRITE_INT_FIELD(uniqNumCols);
+	WRITE_ATTRNUMBER_ARRAY(uniqColIdx, node->uniqNumCols);
+	WRITE_OID_ARRAY(uniqOperators, node->uniqNumCols);
+	WRITE_OID_ARRAY(uniqCollations, node->uniqNumCols);
 }
 
 static void
@@ -2741,6 +2746,7 @@ _outSelectStmt(StringInfo str, const SelectStmt *node)
 	WRITE_NODE_FIELD(sortClause);
 	WRITE_NODE_FIELD(limitOffset);
 	WRITE_NODE_FIELD(limitCount);
+	WRITE_ENUM_FIELD(limitOption, LimitOption);
 	WRITE_NODE_FIELD(lockingClause);
 	WRITE_NODE_FIELD(withClause);
 	WRITE_ENUM_FIELD(op, SetOperation);
@@ -2952,6 +2958,7 @@ _outQuery(StringInfo str, const Query *node)
 	WRITE_NODE_FIELD(sortClause);
 	WRITE_NODE_FIELD(limitOffset);
 	WRITE_NODE_FIELD(limitCount);
+	WRITE_ENUM_FIELD(limitOption, LimitOption);
 	WRITE_NODE_FIELD(rowMarks);
 	WRITE_NODE_FIELD(setOperations);
 	WRITE_NODE_FIELD(constraintDeps);
diff --git a/src/backend/nodes/readfuncs.c b/src/backend/nodes/readfuncs.c
index 2a2f39bf047..644e0f5fc73 100644
--- a/src/backend/nodes/readfuncs.c
+++ b/src/backend/nodes/readfuncs.c
@@ -278,6 +278,7 @@ _readQuery(void)
 	READ_NODE_FIELD(sortClause);
 	READ_NODE_FIELD(limitOffset);
 	READ_NODE_FIELD(limitCount);
+	READ_ENUM_FIELD(limitOption, LimitOption);
 	READ_NODE_FIELD(rowMarks);
 	READ_NODE_FIELD(setOperations);
 	READ_NODE_FIELD(constraintDeps);
@@ -2398,6 +2399,11 @@ _readLimit(void)
 
 	READ_NODE_FIELD(limitOffset);
 	READ_NODE_FIELD(limitCount);
+	READ_ENUM_FIELD(limitOption, LimitOption);
+	READ_INT_FIELD(uniqNumCols);
+	READ_ATTRNUMBER_ARRAY(uniqColIdx, local_node->uniqNumCols);
+	READ_OID_ARRAY(uniqOperators, local_node->uniqNumCols);
+	READ_OID_ARRAY(uniqCollations, local_node->uniqNumCols);
 
 	READ_DONE();
 }