sql: do not allow SET (ttl_expire_after) if automatic column defined

Note we allow this for CREATE TABLE so SHOW CREATE TABLE round trips.
But we should never need this for the ALTER TABLE ... SET ...

Release note: None

pkg/sql/alter_table.go

@@ -1870,6 +1870,13 @@ func handleTTLStorageParamChange(
 		// Adding a TTL requires adding the automatic column and deferring the TTL
 		// addition to after the column is successfully added.
 		tableDesc.RowLevelTTL = nil
+		if _, err := tableDesc.FindColumnWithName(colinfo.TTLDefaultExpirationColumnName); err == nil {
+			return pgerror.Newf(
+				pgcode.InvalidTableDefinition,
+				"cannot add TTL to table with the %s column already defined",
+				colinfo.TTLDefaultExpirationColumnName,
+			)
+		}
 		col, err := rowLevelTTLAutomaticColumnDef(after)
 		if err != nil {
 			return err

pkg/sql/logictest/testdata/logic_test/row_level_ttl

@@ -399,6 +399,19 @@ CREATE TABLE public.tbl (
                                                                                             FAMILY fam_0_id_text_crdb_internal_expiration (id, text, crdb_internal_expiration)
 ) WITH (ttl = 'on', ttl_automatic_column = 'on', ttl_expire_after = '00:10:00':::INTERVAL)
 
+# Test adding to TTL table with crdb_internal_expiration already defined.
+statement ok
+DROP TABLE tbl;
+CREATE TABLE tbl (
+  id INT PRIMARY KEY,
+  text TEXT,
+  crdb_internal_expiration TIMESTAMPTZ,
+  FAMILY (id, text)
+)
+
+statement error cannot add TTL to table with the crdb_internal_expiration column already defined
+ALTER TABLE tbl SET (ttl_expire_after = '10 minutes')
+
 # Test we cannot add FKs to a TTL table.
 statement ok
 CREATE TABLE ref_table (id INT PRIMARY KEY, ref INT)