Fix Oracle ALTER COLUMN syntax for Element identifiers

docs/migration-guide-12.1-to-13.md

@@ -305,7 +305,11 @@ a UNIQUE table clause. No ownership decision may be inferred from that syntax.
 Oracle now rejects nonempty `Index.IncludeColumns` and `Index.Clustered = true` before
 DDL. Version 12.1 silently ignored them. Remove these options for an ordinary Oracle
 index or author an explicit Oracle-specific design; a SQL Server clustered-index
-request is not translated to an Oracle index-organized table.
+request is not translated to an Oracle index-organized table.
+
+Oracle column changes and default removal use `MODIFY (...)`. This disambiguates
+valid column names such as `Element`, which Oracle can interpret as syntax in the
+unparenthesized form, rejecting the statement with ORA-00903 or ORA-01735.
 
 Structured metadata preserves SQL Server nonclustered primary keys and Oracle
 ordered foreign-key pairs/delete actions. Foreign-key constructor arrays are copied,

src/Migrator.Tests/Providers/OracleProvider/OracleDefaultSyntaxTests.cs

@@ -0,0 +1,43 @@
+using System;
+using System.Data;
+using DotNetProjects.Migrator.Framework;
+using DotNetProjects.Migrator.Providers.Impl.Oracle;
+using Migrator.Tests.Settings;
+using NUnit.Framework;
+using Oracle.ManagedDataAccess.Client;
+
+namespace Migrator.Tests.Providers.OracleProvider;
+
+[TestFixture]
+[Category("Oracle")]
+public class OracleDefaultSyntaxTests
+{
+    [TestCase(false)]
+    [TestCase(true)]
+    public void ElementColumnDefaultCanBeRemoved(bool throughChangeColumn)
+    {
+        var connectionString = new ConfigurationReader().GetDatabaseConnectionConfigById("Oracle")?.ConnectionString;
+        if (string.IsNullOrEmpty(connectionString)) Assert.Ignore("No Oracle connection configured.");
+        using var connection = new OracleConnection(connectionString);
+        connection.Open();
+        using var provider = new OracleTransformationProvider(new OracleDialect(), connection, null, "default", "Oracle.ManagedDataAccess.Client");
+        var table = "Default_" + Guid.NewGuid().ToString("N")[..12];
+        provider.AddTable(table, new Column("Id", DbType.Int32),
+            new Column("Element", DbType.String, 32) { DefaultValue = "fallback" });
+        try
+        {
+            provider.Insert(table, ["Id"], [1]);
+            if (throughChangeColumn)
+                provider.ChangeColumn(table, new Column("Element", DbType.String, 64));
+            else
+                provider.RemoveColumnDefaultValue(table, "Element");
+            provider.Insert(table, ["Id"], [2]);
+            Assert.That(provider.ExecuteScalar("SELECT Element FROM " + table + " WHERE Id=1"), Is.EqualTo("fallback"));
+            Assert.That(provider.ExecuteScalar("SELECT Element FROM " + table + " WHERE Id=2"), Is.EqualTo(DBNull.Value));
+        }
+        finally
+        {
+            provider.RemoveTable(table);
+        }
+    }
+}

src/Migrator/Providers/Impl/Oracle/OracleTransformationProvider.cs

@@ -248,7 +248,7 @@
 
         table = QuoteTableNameIfRequired(table);
 
-        ExecuteNonQuery(string.Format("ALTER TABLE {0} MODIFY {1}", table, sqlColumn));
+        ExecuteNonQuery(string.Format("ALTER TABLE {0} MODIFY ({1})", table, sqlColumn));
     }
 
     public override void AddColumn(string table, string sqlColumn)
@@ -300,7 +300,7 @@
         return tables.ToArray();
     }
 
     public override Column[] GetColumns(string table)
     {
         var stringBuilder = new StringBuilder();
         stringBuilder.AppendLine("SELECT");
@@ -655,7 +655,7 @@
 
     public override void RemoveColumnDefaultValue(string table, string column)
     {
-        var sql = string.Format("ALTER TABLE {0} MODIFY {1} DEFAULT NULL", QuoteTableNameIfRequired(table), QuoteColumnNameIfRequired(column));
+        var sql = string.Format("ALTER TABLE {0} MODIFY ({1} DEFAULT NULL)", QuoteTableNameIfRequired(table), QuoteColumnNameIfRequired(column));
         ExecuteNonQuery(sql);
     }