Support Informix trailing constraint names and share constraint rendering

README.md

@@ -141,6 +141,7 @@ and missing syntax gets added on demand — [open an issue](https://github.com/J
 | **DML** | `INSERT` · `UPDATE` · `UPSERT` · `MERGE` · `DELETE` · `TRUNCATE TABLE` |
 | **DDL** | `CREATE …` · `ALTER …` · `DROP …` |
 | **PostgreSQL RLS** | `CREATE POLICY` · `ALTER TABLE … ENABLE`/`DISABLE`/`FORCE`/`NO FORCE ROW LEVEL SECURITY` |
+| **Informix constraints** | `ALTER TABLE … ADD CONSTRAINT` with trailing constraint names for primary, unique, foreign and check constraints; enable with `parser.withDialect(Dialect.INFORMIX)` |
 | **Salesforce SOQL** | `INCLUDES` · `EXCLUDES` |
 
 Beyond statement shapes, the grammar handles nested sub-selects, bind parameters (`?`,

src/main/java/net/sf/jsqlparser/parser/AbstractJSqlParser.java

@@ -45,7 +45,7 @@ public enum Dialect {
                                                         AdjacentStringLiterals.WHITESPACE,
                                                         Feature.allowDoubleQuotedStrings,
                                                         Feature.allowBackslashEscapeCharacter), SNOWFLAKE(
-                                                                Feature.allowBackslashEscapeCharacter);
+                                                                Feature.allowBackslashEscapeCharacter), INFORMIX;
 
         private final Set<Feature> lexerFeatures;
         private final AdjacentStringLiterals adjacentStringLiterals;

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

@@ -54,17 +54,12 @@ public void setEnforced(Boolean enforced) {
     @Override
     public String toString() {
         StringBuilder b = new StringBuilder();
-        if (isUseConstraintKeyword() || getName() != null) {
-            b.append("CONSTRAINT");
-            if (getName() != null) {
-                b.append(" ").append(getName());
-            }
-            b.append(" ");
-        }
+        appendConstraintPrefixTo(b);
         b.append("CHECK (").append(expression).append(")");
         if (enforced != null) {
             b.append(enforced ? " ENFORCED" : " NOT ENFORCED");
         }
+        appendConstraintSuffixTo(b);
         appendConstraintAttributesTo(b);
         return b.toString();
     }

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

@@ -174,6 +174,7 @@ public String toString() {
                     .append(PlainSelect.getStringList(getReferencedColumnNames(), true, true));
             referentialActions.forEach(b::append);
         }
+        appendConstraintSuffixTo(b);
         appendConstraintAttributesTo(b);
         return b.toString();
     }

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

@@ -18,6 +18,45 @@ public class NamedConstraint extends Index {
 
     private String indexName;
     private boolean useConstraintKeyword;
+    private ConstraintNamePosition constraintNamePosition = ConstraintNamePosition.BEFORE;
+
+    /** Position of the constraint symbol relative to its definition. */
+    public enum ConstraintNamePosition {
+        BEFORE, AFTER
+    }
+
+    public ConstraintNamePosition getConstraintNamePosition() {
+        return constraintNamePosition;
+    }
+
+    public void setConstraintNamePosition(ConstraintNamePosition position) {
+        constraintNamePosition = java.util.Objects.requireNonNull(position, "position");
+    }
+
+    public NamedConstraint withConstraintNamePosition(ConstraintNamePosition position) {
+        setConstraintNamePosition(position);
+        return this;
+    }
+
+    /** Appends the leading keyword and, for the usual syntax, the constraint name. */
+    public void appendConstraintPrefixTo(StringBuilder builder) {
+        boolean leadingName = getName() != null
+                && constraintNamePosition == ConstraintNamePosition.BEFORE;
+        if (useConstraintKeyword || leadingName) {
+            builder.append("CONSTRAINT");
+            if (leadingName) {
+                builder.append(' ').append(getName());
+            }
+            builder.append(' ');
+        }
+    }
+
+    /** Appends an Informix constraint name after the complete constraint definition. */
+    public void appendConstraintSuffixTo(StringBuilder builder) {
+        if (constraintNamePosition == ConstraintNamePosition.AFTER && getName() != null) {
+            builder.append(" CONSTRAINT ").append(getName());
+        }
+    }
 
     /**
      * Returns the optional index name declared after the constraint type. This is distinct from
@@ -44,9 +83,6 @@ public void setUseConstraintKeyword(boolean useConstraintKeyword) {
     @Override
     public String toString() {
         String idxSpecText = PlainSelect.getStringList(getIndexSpec(), false, false);
-        String head = useConstraintKeyword || getName() != null
-                ? "CONSTRAINT" + (getName() != null ? " " + getName() : "") + " "
-                : "";
         String keyword = getIndexKeyword() != null
                 && !getType().toUpperCase(java.util.Locale.ROOT)
                         .endsWith(getIndexKeyword().toUpperCase(java.util.Locale.ROOT))
@@ -61,9 +97,12 @@ public String toString() {
                         : " " + PlainSelect.getStringList(getColumnsNames(), true, true))
                 +
                 (!"".equals(idxSpecText) ? " " + idxSpecText : "");
-        StringBuilder sql = new StringBuilder(head).append(tail);
+        StringBuilder sql = new StringBuilder();
+        appendConstraintPrefixTo(sql);
+        sql.append(tail);
         appendConstraintOptionsTo(sql);
         if (getKind() != Kind.FOREIGN_KEY) {
+            appendConstraintSuffixTo(sql);
             appendConstraintAttributesTo(sql);
         }
         return sql.toString();

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

@@ -94,13 +94,7 @@ private void deParseExclude(ExcludeConstraint constraint) {
     }
 
     private void deParseCheck(CheckConstraint constraint) {
-        if (constraint.getName() != null || constraint.isUseConstraintKeyword()) {
-            builder.append("CONSTRAINT");
-            if (constraint.getName() != null) {
-                builder.append(' ').append(constraint.getName());
-            }
-            builder.append(' ');
-        }
+        constraint.appendConstraintPrefixTo(builder);
         builder.append("CHECK (");
         if (constraint.getExpression() != null) {
             constraint.getExpression().accept(expressionVisitor, null);
@@ -111,6 +105,7 @@ private void deParseCheck(CheckConstraint constraint) {
         if (constraint.getEnforced() != null) {
             builder.append(constraint.getEnforced() ? " ENFORCED" : " NOT ENFORCED");
         }
+        constraint.appendConstraintSuffixTo(builder);
         constraint.appendConstraintAttributesTo(builder);
     }
 }

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

@@ -14403,6 +14403,36 @@ DefaultConstraint DefaultConstraintSpec():
     { return constraint; }
 }
 
+/** Parses Informix's ADD CONSTRAINT definition [CONSTRAINT name]. */
+NamedConstraint InformixConstraint():
+{
+    NamedConstraint constraint;
+    Token type;
+    List<String> columns;
+    String name;
+}
+{
+    <K_CONSTRAINT>
+    (
+        ( type=<K_PRIMARY> <K_KEY> | type=<K_UNIQUE> )
+        columns=ColumnsNamesList() {
+            constraint = new NamedConstraint()
+                    .withType(type.kind == K_PRIMARY ? "PRIMARY KEY" : type.image)
+                    .withColumnsNames(columns);
+        }
+        |
+        constraint=ForeignKeySpec(null)
+        |
+        constraint=CheckConstraintSpec(null)
+    )
+    [ <K_CONSTRAINT> name=RelObjectName() { constraint.setName(name); } ]
+    {
+        constraint.setUseConstraintKeyword(true);
+        constraint.setConstraintNamePosition(NamedConstraint.ConstraintNamePosition.AFTER);
+        return constraint;
+    }
+}
+
 /**
  * Parses ADD/ALTER CONSTRAINT clause within AlterExpression.
  * Handles: CONSTRAINT [UNIQUE [KEY|INDEX]] name columns
@@ -14703,6 +14733,15 @@ AlterExpression AlterExpressionAddAlterModify():
             alterExp.setIndex(index);
         }
         |
+        LOOKAHEAD(<K_CONSTRAINT> (<K_PRIMARY> <K_KEY> | <K_FOREIGN> <K_KEY>
+                | <K_UNIQUE> | <K_CHECK>) "(",
+                { Dialect.INFORMIX.name().equals(getAsString(Feature.dialect)) })
+        index=InformixConstraint() {
+            requireDdlSyntax(alterExp.getOperation() == AlterOperation.ADD,
+                    "Informix constraint definitions require ADD");
+            alterExp.setIndex(index);
+        }
+        |
         LOOKAHEAD({ isTableIndexAhead() }) index=TableIndexSpec(false) {
             alterExp.setIndex(index);
             if (index.getKind() == Index.Kind.PRIMARY_KEY) {

src/site/sphinx/usage.rst

@@ -711,9 +711,20 @@ One grammar covers every supported RDBMS, but a few pieces of syntax mean differ
       - ``withDoubleQuotedStrings``, ``withBackslashEscapeCharacter``, any-whitespace rule for adjacent string literals
     * - ``SNOWFLAKE``
       - ``withBackslashEscapeCharacter`` only, double quotes stay quoted identifiers
+    * - ``INFORMIX``
+      - Informix ``ALTER TABLE ... ADD CONSTRAINT`` definitions with optional trailing constraint names
 
 Features set explicitly *after* the preset win over it.
 
+Informix's constraint form requires an explicit dialect selection:
+
+.. code-block:: java
+
+    Statement stmt = CCJSqlParserUtil.parse(
+            "ALTER TABLE child ADD CONSTRAINT FOREIGN KEY (id) "
+                    + "REFERENCES parent(id) CONSTRAINT fk_child",
+            parser -> parser.withDialect(Dialect.INFORMIX));
+
 The individual features
 ------------------------------