#201: fixed 'order by' clause problems (#202)

* #201: Fixed 'ORDER BY' clause problems

jdbc-adapter/virtualschema-jdbc-adapter/src/main/java/com/exasol/adapter/dialects/bigquery/BigQueryQueryRewriter.java

@@ -99,9 +99,11 @@ private void appendColumnValue(final StringBuilder builder, final ResultSet resu
         case Types.TIMESTAMP:
             appendTimestamp(builder, resultSet, columnName);
             break;
-        case Types.VARBINARY:
-        case Types.TIME:
         case Types.VARCHAR:
+            builder.append(this.dialect.getStringLiteral(resultSet.getString(columnName)));
+            break;
+        case Types.TIME:
+        case Types.VARBINARY:
         default:
             appendString(builder, resultSet, columnName);
             break;

jdbc-adapter/virtualschema-jdbc-adapter/src/main/java/com/exasol/adapter/dialects/bigquery/BigQuerySqlDialect.java

@@ -136,4 +136,9 @@ public boolean requiresSchemaQualifiedTableNames(final SqlGenerationContext cont
     public NullSorting getDefaultNullSorting() {
         return NullSorting.NULLS_SORTED_AT_END;
     }
+
+    @Override
+    public SqlGenerationVisitor getSqlGenerationVisitor(final SqlGenerationContext context) {
+        return new BigQuerySqlGenerationVisitor(this, context);
+    }
 }

jdbc-adapter/virtualschema-jdbc-adapter/src/main/java/com/exasol/adapter/dialects/bigquery/BigQuerySqlGenerationVisitor.java

@@ -0,0 +1,33 @@
+package com.exasol.adapter.dialects.bigquery;
+
+import com.exasol.adapter.*;
+import com.exasol.adapter.dialects.*;
+import com.exasol.adapter.sql.*;
+
+import java.util.*;
+
+/**
+ * This class implements a Google-Big-Query-specific variant of a SQL generation visitor.
+ */
+public class BigQuerySqlGenerationVisitor extends SqlGenerationVisitor {
+    /**
+     * Create a new instance of {@link BigQuerySqlGenerationVisitor}.
+     * 
+     * @param dialect SQL dialect
+     * @param context SQL generation context
+     */
+    public BigQuerySqlGenerationVisitor(final SqlDialect dialect, final SqlGenerationContext context) {
+        super(dialect, context);
+    }
+
+    @Override
+    public String visit(final SqlOrderBy orderBy) throws AdapterException {
+        final List<String> sqlOrderElement = new ArrayList<>();
+        for (int i = 0; i < orderBy.getExpressions().size(); ++i) {
+            final boolean isAscending = orderBy.isAscending().get(i);
+            final String elementSql = orderBy.getExpressions().get(i).accept(this) + (isAscending ? "" : " DESC");
+            sqlOrderElement.add(elementSql);
+        }
+        return "ORDER BY " + String.join(", ", sqlOrderElement);
+    }
+}