fixes #918

Author: wumpz

src/main/java/net/sf/jsqlparser/statement/alter/AlterExpression.java

@@ -26,6 +26,7 @@ public class AlterExpression {
     //private ColDataType dataType;
 
     private List<ColumnDataType> colDataTypeList;
+    private List<ColumnDropNotNull> columnDropNotNullList;
 
     private List<String> pkColumns;
     private List<String> ukColumns;
@@ -115,6 +116,13 @@ public void addColDataType(ColumnDataType columnDataType) {
         }
         colDataTypeList.add(columnDataType);
     }
+    
+    public void addColDropNotNull(ColumnDropNotNull columnDropNotNull) {
+        if (columnDropNotNullList == null) {
+            columnDropNotNullList = new ArrayList<ColumnDropNotNull>();
+        }
+        columnDropNotNullList.add(columnDropNotNull);
+    }
 
     public List<String> getFkSourceColumns() {
         return fkSourceColumns;
@@ -196,6 +204,10 @@ public void setConstraints(List<ConstraintState> constraints) {
         this.constraints = constraints;
     }
 
+    public List<ColumnDropNotNull> getColumnDropNotNullList() {
+        return columnDropNotNullList;
+    }
+
     public void addParameters(String... params) {
         if (parameters == null) {
             parameters = new ArrayList<String>();
@@ -247,6 +259,21 @@ public String toString() {
             if (colDataTypeList.size() > 1) {
                 b.append(")");
             }
+        } else if ( getColumnDropNotNullList() != null) {
+            if (operation == AlterOperation.CHANGE) {
+                if (optionalSpecifier != null) {
+                    b.append(optionalSpecifier).append(" ");
+                }
+                b.append(columnOldName).append(" ");
+            } else if (columnDropNotNullList.size() > 1) {
+                b.append("(");
+            } else {
+                b.append("COLUMN ");
+            }
+            b.append(PlainSelect.getStringList(columnDropNotNullList));
+            if (columnDropNotNullList.size() > 1) {
+                b.append(")");
+            }
         } else if (constraintName != null) {
             b.append("CONSTRAINT ");
             if (constraintIfExists) {
@@ -335,4 +362,28 @@ private String parametersToString() {
         }
     }
 
+    public static class ColumnDropNotNull {
+
+        private final String columnName;
+        private final boolean withNot;
+
+        public ColumnDropNotNull(String columnName, boolean withNot) {
+            this.columnName = columnName;
+            this.withNot = withNot;
+        }
+
+        public String getColumnName() {
+            return columnName;
+        }
+
+        public boolean isWithNot() {
+            return withNot;
+        }
+
+        @Override
+        public String toString() {
+            return columnName + " DROP" +
+                     (withNot ? " NOT " : " ") + "NULL";
+        }
+    }
 }

src/main/jjtree/net/sf/jsqlparser/parser/JSqlParserCC.jjt

@@ -4133,6 +4133,24 @@ AlterExpression.ColumnDataType AlterExpressionColumnDataType():
     }
 }
 
+AlterExpression.ColumnDropNotNull AlterExpressionColumnDropNotNull():
+{
+    String columnName = null;
+    boolean withNot = false;
+    ColDataType dataType = null;
+    List<String> columnSpecs = null;
+    List<String> parameter = null;
+}
+{
+    columnName = RelObjectName()
+    <K_DROP>
+    (<K_NOT> { withNot = true; } )?
+    <K_NULL>
+    {
+        return new AlterExpression.ColumnDropNotNull(columnName, withNot);
+    }
+}
+
 List<ConstraintState> AlterExpressionConstraintState():
 {
     List<ConstraintState> retval = new ArrayList<ConstraintState>();
@@ -4184,6 +4202,7 @@ AlterExpression AlterExpression():
     Index index = null;
     Table fkTable = null;
     AlterExpression.ColumnDataType alterExpressionColumnDataType = null;
+    AlterExpression.ColumnDropNotNull alterExpressionColumnDropNotNull = null;
 }
 {
 
@@ -4211,7 +4230,9 @@ AlterExpression AlterExpression():
         )
 		|
         ( (LOOKAHEAD(2) <K_COLUMN>)?
-            alterExpressionColumnDataType = AlterExpressionColumnDataType() { alterExp.addColDataType(alterExpressionColumnDataType); }
+            (LOOKAHEAD(2) alterExpressionColumnDataType = AlterExpressionColumnDataType() { alterExp.addColDataType(alterExpressionColumnDataType); }
+            |
+            alterExpressionColumnDropNotNull = AlterExpressionColumnDropNotNull() { alterExp.addColDropNotNull( alterExpressionColumnDropNotNull); })
         )
         |
         (

src/test/java/net/sf/jsqlparser/statement/alter/AlterTest.java

@@ -388,4 +388,9 @@ public void testIssue259() throws JSQLParserException {
     public void testIssue633_2() throws JSQLParserException {
         assertSqlCanBeParsedAndDeparsed("CREATE INDEX idx_american_football_action_plays_1 ON american_football_action_plays USING btree (play_type)");
     }
+    
+    @Test
+    public void testAlterTableAlterColumnDropNotNullIssue918() throws JSQLParserException {
+        assertSqlCanBeParsedAndDeparsed("ALTER TABLE \"user_table_t\" ALTER COLUMN name DROP NOT NULL");
+    }
 }