From 485a5d0ae3274a83a36788290b3bdc4d973387b4 Mon Sep 17 00:00:00 2001
From: Mihai Budiu <mbudiu@gmail.com>
Date: Thu, 12 Oct 2023 13:25:57 -0700
Subject: [PATCH] [CALCITE-6006] RelToSqlConverter loses charset information

Signed-off-by: Mihai Budiu <mbudiu@gmail.com>
---
 .../calcite/rel/rel2sql/SqlImplementor.java      | 16 +++++++++++++++-
 .../rel/rel2sql/RelToSqlConverterTest.java       | 12 ++++++++++++
 2 files changed, 27 insertions(+), 1 deletion(-)

diff --git a/core/src/main/java/org/apache/calcite/rel/rel2sql/SqlImplementor.java b/core/src/main/java/org/apache/calcite/rel/rel2sql/SqlImplementor.java
index 16455ff2f622..573c497885f4 100644
--- a/core/src/main/java/org/apache/calcite/rel/rel2sql/SqlImplementor.java
+++ b/core/src/main/java/org/apache/calcite/rel/rel2sql/SqlImplementor.java
@@ -16,6 +16,7 @@
  */
 package org.apache.calcite.rel.rel2sql;
 
+import org.apache.calcite.config.CalciteSystemProperty;
 import org.apache.calcite.linq4j.Ord;
 import org.apache.calcite.linq4j.tree.Expressions;
 import org.apache.calcite.plan.RelOptUtil;
@@ -90,6 +91,7 @@
 import org.apache.calcite.sql.validate.SqlValidatorUtil;
 import org.apache.calcite.util.DateString;
 import org.apache.calcite.util.ImmutableBitSet;
+import org.apache.calcite.util.NlsString;
 import org.apache.calcite.util.Pair;
 import org.apache.calcite.util.RangeSets;
 import org.apache.calcite.util.Sarg;
@@ -1409,8 +1411,20 @@ public static SqlNode toSql(RexLiteral literal) {
             () -> "literal " + literal
                 + " has null SqlTypeFamily, and is SqlTypeName is " + typeName);
     switch (family) {
-    case CHARACTER:
+    case CHARACTER: {
+      final NlsString value = literal.getValueAs(NlsString.class);
+      if (value != null) {
+        final String defaultCharset = CalciteSystemProperty.DEFAULT_CHARSET.value();
+        final String charsetName = value.getCharsetName();
+        if (!defaultCharset.equals(charsetName)) {
+          // Set the charset only if it is not the same as the default charset
+          return SqlLiteral.createCharString(
+              castNonNull(value).getValue(), charsetName, POS);
+        }
+      }
+      // Create a string without specifying a charset
       return SqlLiteral.createCharString((String) castNonNull(literal.getValue2()), POS);
+    }
     case NUMERIC:
     case EXACT_NUMERIC:
       return SqlLiteral.createExactNumeric(
diff --git a/core/src/test/java/org/apache/calcite/rel/rel2sql/RelToSqlConverterTest.java b/core/src/test/java/org/apache/calcite/rel/rel2sql/RelToSqlConverterTest.java
index 661f7163cb26..0e97580cb6fe 100644
--- a/core/src/test/java/org/apache/calcite/rel/rel2sql/RelToSqlConverterTest.java
+++ b/core/src/test/java/org/apache/calcite/rel/rel2sql/RelToSqlConverterTest.java
@@ -83,6 +83,7 @@
 import org.apache.calcite.tools.RelBuilder;
 import org.apache.calcite.tools.RuleSet;
 import org.apache.calcite.tools.RuleSets;
+import org.apache.calcite.util.ConversionUtil;
 import org.apache.calcite.util.ImmutableBitSet;
 import org.apache.calcite.util.TestUtil;
 import org.apache.calcite.util.Util;
@@ -282,6 +283,17 @@ private static String toSql(RelNode root, SqlDialect dialect,
     sql(query).ok(expected);
   }
 
+  /** Test case for <a href="https://issues.apache.org/jira/browse/CALCITE-6006">[CALCITE-6006]</a>
+   * RelToSqlConverter loses charset information. */
+  @Test void testCharset() {
+    sql("select _UTF8'\u4F60\u597D'")
+        .withMysql() // produces a simpler output query
+        .ok("SELECT _UTF-8'\u4F60\u597D'");
+    sql("select _UTF16'" + ConversionUtil.TEST_UNICODE_STRING + "'")
+        .withMysql()
+        .ok("SELECT _UTF-16LE'" + ConversionUtil.TEST_UNICODE_STRING + "'");
+  }
+
   /** Test case for
    * <a href="https://issues.apache.org/jira/browse/CALCITE-4321">[CALCITE-4321]
    * JDBC adapter omits FILTER (WHERE ...) expressions when generating SQL</a>