SQL: Fix ANTL4 Grammar ambiguities.

x-pack/plugin/sql/src/main/antlr/SqlBase.g4

@@ -218,11 +218,9 @@ primaryExpression
     : castExpression                                                                 #cast
     | extractExpression                                                              #extract
     | constant                                                                       #constantDefault
-    | ASTERISK                                                                       #star
     | (qualifiedName DOT)? ASTERISK                                                  #star
     | functionExpression                                                             #function
     | '(' query ')'                                                                  #subqueryExpression
-    | identifier                                                                     #columnReference
     | qualifiedName                                                                  #dereference
     | '(' expression ')'                                                             #parenthesizedExpression
     ;

x-pack/plugin/sql/src/main/java/org/elasticsearch/xpack/sql/parser/ExpressionBuilder.java

@@ -51,7 +51,6 @@
 import org.elasticsearch.xpack.sql.parser.SqlBaseParser.BooleanLiteralContext;
 import org.elasticsearch.xpack.sql.parser.SqlBaseParser.CastExpressionContext;
 import org.elasticsearch.xpack.sql.parser.SqlBaseParser.CastTemplateContext;
-import org.elasticsearch.xpack.sql.parser.SqlBaseParser.ColumnReferenceContext;
 import org.elasticsearch.xpack.sql.parser.SqlBaseParser.ComparisonContext;
 import org.elasticsearch.xpack.sql.parser.SqlBaseParser.DateEscapedLiteralContext;
 import org.elasticsearch.xpack.sql.parser.SqlBaseParser.DecimalLiteralContext;
@@ -142,11 +141,6 @@ public Expression visitStar(StarContext ctx) {
                 new UnresolvedAttribute(source(ctx.qualifiedName()), visitQualifiedName(ctx.qualifiedName())) : null);
     }
 
-    @Override
-    public Object visitColumnReference(ColumnReferenceContext ctx) {
-        return new UnresolvedAttribute(source(ctx), visitIdentifier(ctx.identifier()));
-    }
-
     @Override
     public Object visitDereference(DereferenceContext ctx) {
         return new UnresolvedAttribute(source(ctx), visitQualifiedName(ctx.qualifiedName()));

x-pack/plugin/sql/src/main/java/org/elasticsearch/xpack/sql/parser/SqlBaseBaseListener.java

@@ -719,18 +719,6 @@ class SqlBaseBaseListener implements SqlBaseListener {
    * <p>The default implementation does nothing.</p>
    */
   @Override public void exitSubqueryExpression(SqlBaseParser.SubqueryExpressionContext ctx) { }
-  /**
-   * {@inheritDoc}
-   *
-   * <p>The default implementation does nothing.</p>
-   */
-  @Override public void enterColumnReference(SqlBaseParser.ColumnReferenceContext ctx) { }
-  /**
-   * {@inheritDoc}
-   *
-   * <p>The default implementation does nothing.</p>
-   */
-  @Override public void exitColumnReference(SqlBaseParser.ColumnReferenceContext ctx) { }
   /**
    * {@inheritDoc}
    *

x-pack/plugin/sql/src/main/java/org/elasticsearch/xpack/sql/parser/SqlBaseBaseVisitor.java

@@ -424,13 +424,6 @@ class SqlBaseBaseVisitor<T> extends AbstractParseTreeVisitor<T> implements SqlBa
    * {@link #visitChildren} on {@code ctx}.</p>
    */
   @Override public T visitSubqueryExpression(SqlBaseParser.SubqueryExpressionContext ctx) { return visitChildren(ctx); }
-  /**
-   * {@inheritDoc}
-   *
-   * <p>The default implementation returns the result of calling
-   * {@link #visitChildren} on {@code ctx}.</p>
-   */
-  @Override public T visitColumnReference(SqlBaseParser.ColumnReferenceContext ctx) { return visitChildren(ctx); }
   /**
    * {@inheritDoc}
    *

x-pack/plugin/sql/src/main/java/org/elasticsearch/xpack/sql/parser/SqlBaseListener.java

@@ -669,18 +669,6 @@ interface SqlBaseListener extends ParseTreeListener {
    * @param ctx the parse tree
    */
   void exitSubqueryExpression(SqlBaseParser.SubqueryExpressionContext ctx);
-  /**
-   * Enter a parse tree produced by the {@code columnReference}
-   * labeled alternative in {@link SqlBaseParser#primaryExpression}.
-   * @param ctx the parse tree
-   */
-  void enterColumnReference(SqlBaseParser.ColumnReferenceContext ctx);
-  /**
-   * Exit a parse tree produced by the {@code columnReference}
-   * labeled alternative in {@link SqlBaseParser#primaryExpression}.
-   * @param ctx the parse tree
-   */
-  void exitColumnReference(SqlBaseParser.ColumnReferenceContext ctx);
   /**
    * Enter a parse tree produced by the {@code dereference}
    * labeled alternative in {@link SqlBaseParser#primaryExpression}.