Support SQL Server ALTER TABLE ADD DEFAULT constraints

src/main/java/net/sf/jsqlparser/statement/create/table/DefaultConstraint.java

@@ -0,0 +1,95 @@
+/*-
+ * #%L
+ * JSQLParser library
+ * %%
+ * Copyright (C) 2004 - 2026 JSQLParser
+ * %%
+ * Dual licensed under GNU LGPL 2.1 or Apache License 2.0
+ * #L%
+ */
+package net.sf.jsqlparser.statement.create.table;
+
+import java.util.function.Consumer;
+import net.sf.jsqlparser.expression.Expression;
+import net.sf.jsqlparser.schema.Column;
+
+/** A SQL Server table-level DEFAULT expression FOR a column, with an optional constraint name. */
+public class DefaultConstraint extends NamedConstraint {
+    private Expression expression;
+    private Column column;
+    private boolean withValues;
+
+    public DefaultConstraint() {
+        setType("DEFAULT");
+        setKind(Kind.DEFAULT);
+    }
+
+    public Expression getExpression() {
+        return expression;
+    }
+
+    public void setExpression(Expression expression) {
+        this.expression = expression;
+    }
+
+    public Column getColumn() {
+        return column;
+    }
+
+    public void setColumn(Column column) {
+        this.column = column;
+    }
+
+    public boolean isWithValues() {
+        return withValues;
+    }
+
+    public void setWithValues(boolean withValues) {
+        this.withValues = withValues;
+    }
+
+    public DefaultConstraint withExpression(Expression expression) {
+        setExpression(expression);
+        return this;
+    }
+
+    public DefaultConstraint withColumn(Column column) {
+        setColumn(column);
+        return this;
+    }
+
+    public DefaultConstraint withWithValues(boolean withValues) {
+        setWithValues(withValues);
+        return this;
+    }
+
+    @Override
+    public DefaultConstraint withName(String name) {
+        setName(name);
+        return this;
+    }
+
+    /** Shares rendering with deparsers while allowing both the value and column to be visited. */
+    public void appendTo(StringBuilder builder, Consumer<Expression> expressionWriter) {
+        if (expression == null || column == null) {
+            throw new IllegalStateException("DEFAULT requires an expression and a target column");
+        }
+        if (getName() != null) {
+            builder.append("CONSTRAINT ").append(getName()).append(' ');
+        }
+        builder.append("DEFAULT ");
+        expressionWriter.accept(expression);
+        builder.append(" FOR ");
+        expressionWriter.accept(column);
+        if (withValues) {
+            builder.append(" WITH VALUES");
+        }
+    }
+
+    @Override
+    public String toString() {
+        StringBuilder builder = new StringBuilder();
+        appendTo(builder, builder::append);
+        return builder.toString();
+    }
+}

src/main/java/net/sf/jsqlparser/statement/create/table/Index.java

@@ -24,7 +24,7 @@
 public class Index implements TableElement, Serializable {
 
     public enum Kind {
-        PRIMARY_KEY, UNIQUE, INDEX, FULLTEXT, SPATIAL, FOREIGN_KEY, CHECK, EXCLUDE, OTHER
+        PRIMARY_KEY, UNIQUE, INDEX, FULLTEXT, SPATIAL, FOREIGN_KEY, CHECK, EXCLUDE, DEFAULT, OTHER
     }
 
     private final List<String> name = new ArrayList<>();
@@ -196,6 +196,8 @@ public void setType(String string) {
                 kind = Kind.CHECK;
             } else if (normalized.startsWith("EXCLUDE")) {
                 kind = Kind.EXCLUDE;
+            } else if (normalized.equals("DEFAULT")) {
+                kind = Kind.DEFAULT;
             } else if (normalized.contains("INDEX") || normalized.contains("KEY")) {
                 kind = Kind.INDEX;
             }

src/main/java/net/sf/jsqlparser/util/TableDefinitionTraversal.java

@@ -19,6 +19,7 @@
 import net.sf.jsqlparser.statement.create.table.ColumnDefinition;
 import net.sf.jsqlparser.statement.create.table.ColumnOption;
 import net.sf.jsqlparser.statement.create.table.CreateTable;
+import net.sf.jsqlparser.statement.create.table.DefaultConstraint;
 import net.sf.jsqlparser.statement.create.table.ExcludeConstraint;
 import net.sf.jsqlparser.statement.create.table.ForeignKeyIndex;
 import net.sf.jsqlparser.statement.create.table.Index;
@@ -75,6 +76,11 @@ public static void visit(TableElement element, Consumer<Expression> expressions,
             if (index instanceof CheckConstraint) {
                 accept(((CheckConstraint) index).getExpression(), expressions);
             }
+            if (index instanceof DefaultConstraint) {
+                DefaultConstraint constraint = (DefaultConstraint) index;
+                accept(constraint.getExpression(), expressions);
+                accept(constraint.getColumn(), expressions);
+            }
             if (index instanceof ExcludeConstraint) {
                 accept(((ExcludeConstraint) index).getExpression(), expressions);
             }

src/main/java/net/sf/jsqlparser/util/deparser/AlterDeParser.java

@@ -12,6 +12,7 @@
 import net.sf.jsqlparser.statement.alter.Alter;
 import net.sf.jsqlparser.expression.ExpressionVisitor;
 import net.sf.jsqlparser.statement.alter.AlterExpression;
+import net.sf.jsqlparser.statement.create.table.DefaultConstraint;
 import net.sf.jsqlparser.statement.select.PlainSelect;
 import java.util.Iterator;
 
@@ -47,6 +48,12 @@ public void deParse(Alter alter) {
     }
 
     private void deParseAction(AlterExpression action) {
+        if (action.getIndex() instanceof DefaultConstraint) {
+            builder.append(action.getOperation()).append(' ');
+            new TableElementDeParser(builder, expressionVisitor).deParse(action.getIndex());
+            deParseTail(action);
+            return;
+        }
         if (action.getColDataTypeList() == null || action.getColDataTypeList().size() != 1
                 || action.getColDataTypeList().get(0).getUsingExpression() == null) {
             builder.append(action);
@@ -63,10 +70,17 @@ private void deParseAction(AlterExpression action) {
         builder.append(column.getColumnName()).append(column.isWithType() ? " TYPE " : " ")
                 .append(column.toStringDataTypeAndSpec()).append(" USING ");
         column.getUsingExpression().accept(expressionVisitor, null);
+        deParseTail(action);
+    }
+
+    private void deParseTail(AlterExpression action) {
         if (action.getParameters() != null && !action.getParameters().isEmpty()) {
             builder.append(' ')
                     .append(PlainSelect.getStringList(action.getParameters(), false, false));
         }
+        if (action.getIndex() != null && action.getIndex().getCommentText() != null) {
+            builder.append(" COMMENT ").append(action.getIndex().getCommentText());
+        }
     }
 
 }

src/main/java/net/sf/jsqlparser/util/deparser/TableElementDeParser.java

@@ -14,6 +14,7 @@
 import net.sf.jsqlparser.statement.create.table.CheckConstraint;
 import net.sf.jsqlparser.statement.create.table.ColumnDefinition;
 import net.sf.jsqlparser.statement.create.table.ColumnOption;
+import net.sf.jsqlparser.statement.create.table.DefaultConstraint;
 import net.sf.jsqlparser.statement.create.table.ExcludeConstraint;
 import net.sf.jsqlparser.statement.create.table.Index;
 import net.sf.jsqlparser.statement.create.table.TableElement;
@@ -30,7 +31,10 @@ public TableElementDeParser(StringBuilder builder,
 
     @Override
     public void deParse(TableElement element) {
-        if (element instanceof ExcludeConstraint) {
+        if (element instanceof DefaultConstraint) {
+            ((DefaultConstraint) element).appendTo(builder,
+                    expression -> expression.accept(expressionVisitor, null));
+        } else if (element instanceof ExcludeConstraint) {
             deParseExclude((ExcludeConstraint) element);
         } else if (element instanceof CheckConstraint) {
             deParseCheck((CheckConstraint) element);

src/main/java/net/sf/jsqlparser/util/validation/validator/AlterValidator.java

@@ -19,6 +19,7 @@
 import net.sf.jsqlparser.statement.alter.AlterExpression.ColumnDropNotNull;
 import net.sf.jsqlparser.statement.alter.AlterExpression.ColumnSetNotNull;
 import net.sf.jsqlparser.statement.alter.AlterOperation;
+import net.sf.jsqlparser.statement.create.table.DefaultConstraint;
 import net.sf.jsqlparser.util.TableDefinitionTraversal;
 import net.sf.jsqlparser.util.validation.ValidationCapability;
 import net.sf.jsqlparser.util.validation.ValidationUtil;
@@ -87,7 +88,10 @@ public void validate(Alter alter, AlterExpression e) {
                 validateOptionalColumnNames(c, e.getUkColumns(), NamedObject.uniqueConstraint);
             }
 
-            if (e.getIndex() != null) {
+            if (e.getIndex() instanceof DefaultConstraint) {
+                validateOptionalName(c, NamedObject.constraint, e.getIndex().getName(), null, false,
+                        NamedObject.table);
+            } else if (e.getIndex() != null) {
                 validateName(c, NamedObject.index, e.getIndex().getName());
                 if (e.getIndex().getColumns() != null) {
                     validateOptionalColumnNames(c,

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

@@ -14137,6 +14137,23 @@ AlterExpression AlterExpressionDiscardOrImport():
 }
 
 
+/**
+ * Parses SQL Server's [CONSTRAINT name] DEFAULT expression FOR column [WITH VALUES].
+ */
+DefaultConstraint DefaultConstraintSpec():
+{
+    DefaultConstraint constraint = new DefaultConstraint();
+    String name;
+    Expression expression;
+}
+{
+    [ <K_CONSTRAINT> name=RelObjectName() { constraint.setName(name); } ]
+    <K_DEFAULT> expression=Expression() { constraint.setExpression(expression); }
+    <K_FOR> name=RelObjectName() { constraint.setColumn(new Column(name)); }
+    [ <K_WITH> <K_VALUES> { constraint.setWithValues(true); } ]
+    { return constraint; }
+}
+
 /**
  * Parses ADD/ALTER CONSTRAINT clause within AlterExpression.
  * Handles: CONSTRAINT [UNIQUE [KEY|INDEX]] name columns
@@ -14422,6 +14439,13 @@ AlterExpression AlterExpressionAddAlterModify():
     )
 
     (
+        LOOKAHEAD({ getToken(1).kind == K_DEFAULT || getToken(1).kind == K_CONSTRAINT
+                && getToken(3).kind == K_DEFAULT }) index=DefaultConstraintSpec() {
+            requireDdlSyntax(alterExp.getOperation() == AlterOperation.ADD,
+                    "Table-level DEFAULT constraints require ADD");
+            alterExp.setIndex(index);
+        }
+        |
         LOOKAHEAD({ alterExp.getOperation() == AlterOperation.ALTER
                 && getToken(1).kind == K_INDEX })
         tk=<K_INDEX> sk3=RelObjectName() IndexOptionList(indexSpec) {