[#285] Add support for ALTER SEQUENCE IF EXISTS

h2/src/docsrc/help/help.csv

@@ -210,7 +210,7 @@ ALTER SCHEMA TEST RENAME TO PRODUCTION
 "
 
 "Commands (DDL)","ALTER SEQUENCE","
-ALTER SEQUENCE sequenceName [ RESTART WITH long ] [ INCREMENT BY long ]
+ALTER SEQUENCE [ IF EXISTS ] sequenceName [ RESTART WITH long ] [ INCREMENT BY long ]
 [ MINVALUE long | NOMINVALUE | NO MINVALUE ]
 [ MAXVALUE long | NOMAXVALUE | NO MAXVALUE ]
 [ CYCLE long | NOCYCLE |  NO CYCLE ]

h2/src/main/org/h2/command/Parser.java

@@ -4891,10 +4891,11 @@ public class Parser {
     }
 
     private AlterSequence parseAlterSequence() {
+        boolean ifExists = readIfExists(false);
         String sequenceName = readIdentifierWithSchema();
-        Sequence sequence = getSchema().getSequence(sequenceName);
-        AlterSequence command = new AlterSequence(session, sequence.getSchema());
-        command.setSequence(sequence);
+        AlterSequence command = new AlterSequence(session, getSchema());
+        command.setSequenceName(sequenceName);
+        command.setIfExists(ifExists);
         while (true) {
             if (readIf("RESTART")) {
                 read("WITH");

h2/src/main/org/h2/command/dml/AlterSequence.java

@@ -24,7 +24,9 @@ import org.h2.table.Table;
  */
 public class AlterSequence extends SchemaCommand {
 
+    private boolean ifExists;
     private Table table;
+    private String sequenceName;
     private Sequence sequence;
     private Expression start;
     private Expression increment;
@@ -37,8 +39,12 @@ public class AlterSequence extends SchemaCommand {
         super(session, schema);
     }
 
-    public void setSequence(Sequence sequence) {
-        this.sequence = sequence;
+    public void setIfExists(boolean b) {
+        ifExists = b;
+    }
+
+    public void setSequenceName(String sequenceName) {
+        this.sequenceName = sequenceName;
     }
 
     @Override
@@ -49,7 +55,7 @@ public class AlterSequence extends SchemaCommand {
     public void setColumn(Column column) {
         table = column.getTable();
         sequence = column.getSequence();
-        if (sequence == null) {
+        if (sequence == null && !ifExists) {
             throw DbException.get(ErrorCode.SEQUENCE_NOT_FOUND_1, column.getSQL());
         }
     }
@@ -81,6 +87,16 @@ public class AlterSequence extends SchemaCommand {
     @Override
     public int update() {
         Database db = session.getDatabase();
+        if (sequence == null) {
+            sequence = getSchema().findSequence(sequenceName);
+            if (sequence == null) {
+                if (!ifExists) {
+                    throw DbException.get(ErrorCode.SEQUENCE_NOT_FOUND_1, sequenceName);
+                } else {
+                    return 0;
+                }
+            }
+        }
         if (table != null) {
             session.getUser().checkRight(table, Right.ALL);
         }

h2/src/main/org/h2/res/help.csv

@@ -75,7 +75,7 @@ ALTER SCHEMA schema RENAME TO newSchemaName
 ","
 Renames a schema."
 "Commands (DDL)","ALTER SEQUENCE","
-ALTER SEQUENCE sequenceName [ RESTART WITH long ] [ INCREMENT BY long ]
+ALTER SEQUENCE [ IF EXISTS ] sequenceName [ RESTART WITH long ] [ INCREMENT BY long ]
 [ MINVALUE long | NOMINVALUE | NO MINVALUE ]
 [ MAXVALUE long | NOMAXVALUE | NO MAXVALUE ]
 [ CYCLE long | NOCYCLE |  NO CYCLE ]
@@ -92,6 +92,10 @@ Adds a new column to a table."
 ALTER TABLE tableName ADD constraint [ CHECK | NOCHECK ]
 ","
 Adds a constraint to a table."
+"Commands (DDL)","ALTER TABLE RENAME CONSTRAINT","
+ALTER TABLE tableName RENAME oldConstraintName TO newConstraintName
+","
+Renames a constraint."
 "Commands (DDL)","ALTER TABLE ALTER COLUMN","
 ALTER TABLE tableName ALTER COLUMN columnName
 { { dataType [ DEFAULT expression ] [ [ NOT ] NULL ] [ AUTO_INCREMENT | IDENTITY ] }

h2/src/test/org/h2/test/testScript.sql

@@ -4455,6 +4455,24 @@ create index if not exists idx_id on s.test(id);
 alter index s.idx_id rename to s.index_id;
 > ok
 
+alter sequence if exists s.seq restart with 10;
+> ok
+
+create sequence s.seq cache 0;
+> ok
+
+alter sequence if exists s.seq restart with 3;
+> ok
+
+select s.seq.nextval as x;
+> X
+> -
+> 3
+> rows: 1
+
+drop sequence s.seq;
+> ok
+
 create sequence s.seq cache 0;
 > ok