sql: bugfixes around writing the old primary key in pk changes

This PR fixes two bugs:
* The logic for when to rewrite the old primary key was broken
  resulting in the old primary key not being rewritten in many cases.
* The old primary key being created was not properly dealing with
  its dangling interleave information.

Release note: None

pkg/sql/alter_table.go

@@ -399,7 +399,7 @@ func (n *alterTableNode) startExec(params runParams) error {
 			// Create a new index that indexes everything the old primary index does, but doesn't store anything.
 			// TODO (rohany): is there an easier way of checking if the existing primary index was the
 			//  automatically created one?
-			if len(n.tableDesc.PrimaryIndex.ColumnNames) == 1 && n.tableDesc.PrimaryIndex.ColumnNames[0] != "rowid" {
+			if !(len(n.tableDesc.PrimaryIndex.ColumnNames) == 1 && n.tableDesc.PrimaryIndex.ColumnNames[0] == "rowid") {
 				oldPrimaryIndexCopy := protoutil.Clone(&n.tableDesc.PrimaryIndex).(*sqlbase.IndexDescriptor)
 				name := generateUniqueConstraintName(
 					"old_primary_key",
@@ -408,6 +408,9 @@ func (n *alterTableNode) startExec(params runParams) error {
 				oldPrimaryIndexCopy.Name = name
 				oldPrimaryIndexCopy.StoreColumnIDs = nil
 				oldPrimaryIndexCopy.StoreColumnNames = nil
+				// Make the copy of the old primary index not-interleaved. This decision
+				// can be revisited based on user experience.
+				oldPrimaryIndexCopy.Interleave = sqlbase.InterleaveDescriptor{}
 				if err := addIndexMutationWithSpecificPrimaryKey(n.tableDesc, oldPrimaryIndexCopy, newPrimaryIndexDesc); err != nil {
 					return err
 				}

pkg/sql/logictest/testdata/logic_test/alter_primary_key

@@ -151,6 +151,7 @@ child  CREATE TABLE child (
        y INT8 NOT NULL,
        z INT8 NOT NULL,
        CONSTRAINT "primary" PRIMARY KEY (y ASC, z ASC),
+       UNIQUE INDEX old_primary_key (x ASC, y ASC, z ASC),
        FAMILY fam_0_x_y_z (x, y, z)
 )
 
@@ -194,6 +195,7 @@ child  CREATE TABLE child (
          z INT8 NOT NULL,
          w INT8 NULL,
          CONSTRAINT "primary" PRIMARY KEY (x ASC, y ASC, z ASC),
+         UNIQUE INDEX old_primary_key (x ASC, y ASC),
          INDEX i (x ASC, w ASC) INTERLEAVE IN PARENT parent (x),
          FAMILY fam_0_x_y_z_w (x, y, z, w)
        ) INTERLEAVE IN PARENT parent (x)