adds drop column to drop use case

src/main/kotlin/unibz.cs.semint.kprime/domain/dml/DropColumn.kt

@@ -5,6 +5,9 @@ import com.fasterxml.jackson.dataformat.xml.annotation.JacksonXmlProperty
 
 class DropColumn {
 
+    @JacksonXmlProperty(isAttribute = true)
+    var tableName :String = ""
+
     @JacksonXmlProperty(isAttribute = true)
     var name :String = ""
 }
\ No newline at end of file

src/main/kotlin/unibz.cs.semint.kprime/usecase/common/SQLizeDropUseCase.kt

 package unibz.cs.semint.kprime.usecase.common
 
 import unibz.cs.semint.kprime.domain.ddl.Constraint
-import unibz.cs.semint.kprime.domain.dml.ChangeSet
-import unibz.cs.semint.kprime.domain.dml.DropConstraint
-import unibz.cs.semint.kprime.domain.dml.DropTable
-import unibz.cs.semint.kprime.domain.dml.DropView
+import unibz.cs.semint.kprime.domain.dml.*
 
 class SQLizeDropUseCase {
 
@@ -16,9 +13,15 @@ class SQLizeDropUseCase {
             commands.add(dropViewCommand(dropView))
         for (dropConstraint in changeset.dropConstraint)
             commands.add(dropConstraintCommand(dropConstraint))
+        for (dropColumn in changeset.dropColumn)
+            commands.add(dropColumnsCommand(dropColumn))
         return commands
     }
 
+    private fun dropColumnsCommand(dropColumn: DropColumn): String {
+        return "ALTER TABLE ${dropColumn.tableName} DROP COLUMN ${dropColumn.name};"
+    }
+
     private fun dropConstraintCommand(dropConstraint: DropConstraint): String {
         when(dropConstraint.type) {
             Constraint.TYPE.PRIMARY_KEY.name -> return dropPrimaryKeyCommand(dropConstraint)