From 127dddfe743daaa84242a2a19aa8784a9bc3c11e Mon Sep 17 00:00:00 2001
From: Adriano dos Santos Fernandes <adrianosf@gmail.com>
Date: Wed, 28 Dec 2016 12:57:47 -0200
Subject: [PATCH] Improvement CORE-5431 - Support for DROP IDENTITY clause.

---
 CHANGELOG.md                                   |  3 +++
 doc/sql.extensions/README.identity_columns.txt |  9 ++++++++-
 src/dsql/DdlNodes.epp                          | 15 +++++++++++++++
 src/dsql/DdlNodes.h                            |  2 ++
 src/dsql/parse.y                               |  8 ++++++++
 5 files changed, 36 insertions(+), 1 deletion(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 5a5f09e506f..ebb5776428f 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -25,6 +25,9 @@
 
 ## Improvements
 
+* [CORE-5430](http://tracker.firebirdsql.org/browse/CORE-5431): Support for DROP IDENTITY clause  
+  Contributor(s): Adriano dos Santos Fernandes
+
 * [CORE-5430](http://tracker.firebirdsql.org/browse/CORE-5430): Support for INCREMENT option in identity columns  
   Contributor(s): Adriano dos Santos Fernandes
 
diff --git a/doc/sql.extensions/README.identity_columns.txt b/doc/sql.extensions/README.identity_columns.txt
index acf47a612bd..5e97b5d4058 100644
--- a/doc/sql.extensions/README.identity_columns.txt
+++ b/doc/sql.extensions/README.identity_columns.txt
@@ -19,7 +19,8 @@ Syntax:
 
     <alter column definition> ::=
         <name> RESTART [ WITH <value> ] |
-        <name> SET INCREMENT [ BY ] <value>
+        <name> SET INCREMENT [ BY ] <value> |
+        <name> DROP IDENTITY
 
 Syntax rules:
     - The type of an identity column must be an exact number type with zero scale. That includes:
@@ -74,3 +75,9 @@ select * from objects order by id;
            2 Book
           10 Computer
           15 Pencil
+
+alter table objects
+  alter id set increment by 2;
+
+alter table objects
+  alter id drop identity;
diff --git a/src/dsql/DdlNodes.epp b/src/dsql/DdlNodes.epp
index 7b1149c0774..83740b621be 100644
--- a/src/dsql/DdlNodes.epp
+++ b/src/dsql/DdlNodes.epp
@@ -7847,6 +7847,21 @@ void AlterRelationNode::modifyField(thread_db* tdbb, DsqlCompilerScratch* dsqlSc
 					}
 				END_MODIFY
 			}
+			else if (clause->dropIdentity)
+			{
+				if (RFR.RDB$GENERATOR_NAME.NULL)
+				{
+					// msg 285: "Column @1 is not an identity column"
+					status_exception::raise(Arg::PrivateDyn(285) << field->fld_name);
+				}
+
+				DropSequenceNode::deleteIdentity(tdbb, transaction, RFR.RDB$GENERATOR_NAME);
+
+				MODIFY RFR
+					RFR.RDB$GENERATOR_NAME.NULL = TRUE;
+					RFR.RDB$IDENTITY_TYPE.NULL = TRUE;
+				END_MODIFY
+			}
 			else if (clause->identityRestart || clause->identityIncrement.specified)
 			{
 				bool found = false;
diff --git a/src/dsql/DdlNodes.h b/src/dsql/DdlNodes.h
index 8c688f2e59d..2604a6765f1 100644
--- a/src/dsql/DdlNodes.h
+++ b/src/dsql/DdlNodes.h
@@ -1383,6 +1383,7 @@ class RelationNode : public DdlNode
 			  field(NULL),
 			  defaultValue(NULL),
 			  dropDefault(false),
+			  dropIdentity(false),
 			  identityRestart(false),
 			  computed(NULL)
 		{
@@ -1391,6 +1392,7 @@ class RelationNode : public DdlNode
 		dsql_fld* field;
 		NestConst<ValueSourceClause> defaultValue;
 		bool dropDefault;
+		bool dropIdentity;
 		bool identityRestart;
 		Nullable<SINT64> identityRestartValue;
 		Nullable<SINT64> identityIncrement;
diff --git a/src/dsql/parse.y b/src/dsql/parse.y
index 1bed23b666c..cc978174549 100644
--- a/src/dsql/parse.y
+++ b/src/dsql/parse.y
@@ -3944,6 +3944,14 @@ alter_op($relationNode)
 			clause->identityIncrement = $6;
 			$relationNode->clauses.add(clause);
 		}
+	| col_opt symbol_column_name DROP IDENTITY
+		{
+			RelationNode::AlterColTypeClause* clause = newNode<RelationNode::AlterColTypeClause>();
+			clause->field = newNode<dsql_fld>();
+			clause->field->fld_name = *$2;
+			clause->dropIdentity = true;
+			$relationNode->clauses.add(clause);
+		}
 	| ALTER SQL SECURITY DEFINER
 		{
 			RelationNode::AlterSqlSecurityClause* clause =