[Backport 3.0] Support CASE function with Calcite

core/src/main/java/org/opensearch/sql/analysis/ExpressionAnalyzer.java

@@ -336,7 +336,7 @@ public Expression visitCase(Case node, AnalysisContext context) {
     }
 
     Expression defaultResult =
-        (node.getElseClause() == null) ? null : analyze(node.getElseClause(), context);
+        node.getElseClause().map(elseClause -> analyze(elseClause, context)).orElse(null);
     CaseClause caseClause = new CaseClause(whens, defaultResult);
 
     // To make this simple, require all result type same regardless of implicit convert

core/src/main/java/org/opensearch/sql/ast/dsl/AstDSL.java

@@ -293,7 +293,7 @@ public UnresolvedExpression caseWhen(UnresolvedExpression elseClause, When... wh
    */
   public UnresolvedExpression caseWhen(
       UnresolvedExpression caseValueExpr, UnresolvedExpression elseClause, When... whenClauses) {
-    return new Case(caseValueExpr, Arrays.asList(whenClauses), elseClause);
+    return new Case(caseValueExpr, Arrays.asList(whenClauses), Optional.ofNullable(elseClause));
   }
 
   public UnresolvedExpression cast(UnresolvedExpression expr, Literal type) {

core/src/main/java/org/opensearch/sql/ast/expression/Case.java

@@ -7,6 +7,7 @@
 
 import com.google.common.collect.ImmutableList;
 import java.util.List;
+import java.util.Optional;
 import lombok.AllArgsConstructor;
 import lombok.EqualsAndHashCode;
 import lombok.Getter;
@@ -31,7 +32,7 @@ public class Case extends UnresolvedExpression {
   private final List<When> whenClauses;
 
   /** Expression that represents ELSE statement result. */
-  private final UnresolvedExpression elseClause;
+  private final Optional<UnresolvedExpression> elseClause;
 
   @Override
   public List<? extends Node> getChild() {
@@ -40,10 +41,7 @@ public List<? extends Node> getChild() {
       children.add(caseValue);
     }
     children.addAll(whenClauses);
-
-    if (elseClause != null) {
-      children.add(elseClause);
-    }
+    elseClause.ifPresent(children::add);
     return children.build();
   }
 

core/src/main/java/org/opensearch/sql/calcite/CalciteRexNodeVisitor.java

@@ -11,6 +11,7 @@
 import static org.opensearch.sql.calcite.utils.UserDefinedFunctionUtils.TransferUserDefinedFunction;
 
 import java.math.BigDecimal;
+import java.util.ArrayList;
 import java.util.List;
 import java.util.stream.Collectors;
 import lombok.RequiredArgsConstructor;
@@ -31,6 +32,7 @@
 import org.opensearch.sql.ast.expression.Alias;
 import org.opensearch.sql.ast.expression.And;
 import org.opensearch.sql.ast.expression.Between;
+import org.opensearch.sql.ast.expression.Case;
 import org.opensearch.sql.ast.expression.Cast;
 import org.opensearch.sql.ast.expression.Compare;
 import org.opensearch.sql.ast.expression.EqualTo;
@@ -89,7 +91,18 @@ public RexNode visitLiteral(Literal node, CalcitePlanContext context) {
       case NULL:
         return rexBuilder.makeNullLiteral(typeFactory.createSqlType(SqlTypeName.NULL));
       case STRING:
-        return rexBuilder.makeLiteral(value.toString());
+        if (value.toString().length() == 1) {
+          // To align Spark/PostgreSQL, Char(1) is useful, such as cast('1' to boolean) should
+          // return true
+          return rexBuilder.makeLiteral(
+              value.toString(), typeFactory.createSqlType(SqlTypeName.CHAR));
+        } else {
+          // Specific the type to VARCHAR and allowCast to true, or the STRING will be optimized to
+          // CHAR(n)
+          // which leads to incorrect return type in deriveReturnType of some functions/operators
+          return rexBuilder.makeLiteral(
+              value.toString(), typeFactory.createSqlType(SqlTypeName.VARCHAR), true);
+        }
       case INTEGER:
         return rexBuilder.makeExactLiteral(new BigDecimal((Integer) value));
       case LONG:
@@ -431,6 +444,19 @@ public RexNode visitCast(Cast node, CalcitePlanContext context) {
     return context.rexBuilder.makeCast(nullableType, expr, true, true);
   }
 
+  @Override
+  public RexNode visitCase(Case node, CalcitePlanContext context) {
+    List<RexNode> caseOperands = new ArrayList<>();
+    for (When when : node.getWhenClauses()) {
+      caseOperands.add(analyze(when.getCondition(), context));
+      caseOperands.add(analyze(when.getResult(), context));
+    }
+    RexNode elseExpr =
+        node.getElseClause().map(e -> analyze(e, context)).orElse(context.relBuilder.literal(null));
+    caseOperands.add(elseExpr);
+    return context.rexBuilder.makeCall(SqlStdOperatorTable.CASE, caseOperands);
+  }
+
   /*
    * Unsupported Expressions of PPL with Calcite for OpenSearch 3.0.0-beta
    */

docs/user/ppl/functions/condition.rst

@@ -192,3 +192,49 @@ Example::
     | False  | Nanette   | Bates    |
     | False  | Dale      | Adams    |
     +--------+-----------+----------+
+
+CASE
+------
+
+Description
+>>>>>>>>>>>
+
+Usage: case(condition1, expr1, condition2, expr2, ... conditionN, exprN else default) return expr1 if condition1 is true, or return expr2 if condition2 is true, ... if no condition is true, then return the value of ELSE clause. If the ELSE clause is not defined, it returns NULL.
+
+Argument type: all the supported data type, (NOTE : there is no comma before "else")
+
+Return type: any
+
+Example::
+
+    os> source=accounts | eval result = case(age > 35, firstname, age < 30, lastname else employer) | fields result, firstname, lastname, age, employer
+    fetched rows / total rows = 4/4
+    +--------+-----------+----------+-----+----------+
+    | result | firstname | lastname | age | employer |
+    |--------+-----------+----------+-----+----------|
+    | Pyrami | Amber     | Duke     | 32  | Pyrami   |
+    | Hattie | Hattie    | Bond     | 36  | Netagy   |
+    | Bates  | Nanette   | Bates    | 28  | Quility  |
+    | null   | Dale      | Adams    | 33  | null     |
+    +--------+-----------+----------+-----+----------+
+
+    os> source=accounts | eval result = case(age > 35, firstname, age < 30, lastname) | fields result, firstname, lastname, age
+    fetched rows / total rows = 4/4
+    +--------+-----------+----------+-----+
+    | result | firstname | lastname | age |
+    |--------+-----------+----------+-----|
+    | null   | Amber     | Duke     | 32  |
+    | Hattie | Hattie    | Bond     | 36  |
+    | Bates  | Nanette   | Bates    | 28  |
+    | null   | Dale      | Adams    | 33  |
+    +--------+-----------+----------+-----+
+
+    os> source=accounts | where true = case(age > 35, false, age < 30, false else true) | fields firstname, lastname, age
+    fetched rows / total rows = 2/2
+    +-----------+----------+-----+
+    | firstname | lastname | age |
+    |-----------+----------+-----|
+    | Amber     | Duke     | 32  |
+    | Dale      | Adams    | 33  |
+    +-----------+----------+-----+
+

integ-test/src/test/java/org/opensearch/sql/calcite/standalone/CalcitePPLCaseFunctionIT.java

@@ -0,0 +1,246 @@
+/*
+ * Copyright OpenSearch Contributors
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package org.opensearch.sql.calcite.standalone;
+
+import static org.opensearch.sql.legacy.TestsConstants.TEST_INDEX_WEBLOGS;
+import static org.opensearch.sql.util.MatcherUtils.rows;
+import static org.opensearch.sql.util.MatcherUtils.schema;
+import static org.opensearch.sql.util.MatcherUtils.verifyDataRows;
+import static org.opensearch.sql.util.MatcherUtils.verifySchema;
+
+import java.io.IOException;
+import org.json.JSONObject;
+import org.junit.jupiter.api.Test;
+import org.opensearch.client.Request;
+import org.opensearch.sql.legacy.TestsConstants;
+
+public class CalcitePPLCaseFunctionIT extends CalcitePPLIntegTestCase {
+  @Override
+  public void init() throws IOException {
+    super.init();
+    loadIndex(Index.WEBLOG);
+    appendDataForBadResponse();
+  }
+
+  private void appendDataForBadResponse() throws IOException {
+    Request request1 = new Request("PUT", "/" + TEST_INDEX_WEBLOGS + "/_doc/7?refresh=true");
+    request1.setJsonEntity(
+        "{\"host\": \"::1\", \"method\": \"GET\", \"url\": \"/history/apollo/\", \"response\":"
+            + " \"301\", \"bytes\": \"6245\"}");
+    client().performRequest(request1);
+    Request request2 =
+        new Request("PUT", "/" + TestsConstants.TEST_INDEX_WEBLOGS + "/_doc/8?refresh=true");
+    request2.setJsonEntity(
+        "{\"host\": \"0.0.0.2\", \"method\": \"GET\", \"url\":"
+            + " \"/shuttle/missions/sts-73/mission-sts-73.html\", \"response\": \"500\", \"bytes\":"
+            + " \"4085\"}");
+    client().performRequest(request2);
+    Request request3 =
+        new Request("PUT", "/" + TestsConstants.TEST_INDEX_WEBLOGS + "/_doc/9?refresh=true");
+    request3.setJsonEntity(
+        "{\"host\": \"::3\", \"method\": \"GET\", \"url\": \"/shuttle/countdown/countdown.html\","
+            + " \"response\": \"403\", \"bytes\": \"3985\"}");
+    client().performRequest(request3);
+    Request request4 =
+        new Request("PUT", "/" + TestsConstants.TEST_INDEX_WEBLOGS + "/_doc/10?refresh=true");
+    request4.setJsonEntity(
+        "{\"host\": \"1.2.3.5\", \"method\": \"GET\", \"url\": \"/history/voyager2/\","
+            + " \"response\": null, \"bytes\": \"4321\"}");
+    client().performRequest(request4);
+  }
+
+  @Test
+  public void testCaseWhenWithCast() {
+    JSONObject actual =
+        executeQuery(
+            String.format(
+                """
+                    source=%s
+                    | eval status =
+                        case(
+                            cast(response as int) >= 200 AND cast(response as int) < 300, "Success",
+                            cast(response as int) >= 300 AND cast(response as int) < 400, "Redirection",
+                            cast(response as int) >= 400 AND cast(response as int) < 500, "Client Error",
+                            cast(response as int) >= 500 AND cast(response as int) < 600, "Server Error"
+                            else concat("Incorrect HTTP status code for", url))
+                    | where status != "Success"
+                    """,
+                TEST_INDEX_WEBLOGS));
+    verifySchema(
+        actual,
+        schema("host", "ip"),
+        schema("method", "string"),
+        schema("url", "string"),
+        schema("response", "string"),
+        schema("bytes", "string"),
+        schema("status", "string"));
+    verifyDataRows(
+        actual,
+        rows("::1", "GET", "6245", "301", "/history/apollo/", "Redirection"),
+        rows(
+            "0.0.0.2",
+            "GET",
+            "4085",
+            "500",
+            "/shuttle/missions/sts-73/mission-sts-73.html",
+            "Server Error"),
+        rows("::3", "GET", "3985", "403", "/shuttle/countdown/countdown.html", "Client Error"),
+        rows(
+            "1.2.3.5",
+            "GET",
+            "4321",
+            null,
+            "/history/voyager2/",
+            "Incorrect HTTP status code for/history/voyager2/"));
+  }
+
+  @Test
+  public void testCaseWhenNoElse() {
+    JSONObject actual =
+        executeQuery(
+            String.format(
+                """
+                    source=%s
+                    | eval status =
+                        case(
+                            cast(response as int) >= 200 AND cast(response as int) < 300, "Success",
+                            cast(response as int) >= 300 AND cast(response as int) < 400, "Redirection",
+                            cast(response as int) >= 400 AND cast(response as int) < 500, "Client Error",
+                            cast(response as int) >= 500 AND cast(response as int) < 600, "Server Error")
+                    | where isnull(status) OR status != "Success"
+                    """,
+                TEST_INDEX_WEBLOGS));
+    verifySchema(
+        actual,
+        schema("host", "ip"),
+        schema("method", "string"),
+        schema("url", "string"),
+        schema("response", "string"),
+        schema("bytes", "string"),
+        schema("status", "string"));
+    verifyDataRows(
+        actual,
+        rows("::1", "GET", "6245", "301", "/history/apollo/", "Redirection"),
+        rows(
+            "0.0.0.2",
+            "GET",
+            "4085",
+            "500",
+            "/shuttle/missions/sts-73/mission-sts-73.html",
+            "Server Error"),
+        rows("::3", "GET", "3985", "403", "/shuttle/countdown/countdown.html", "Client Error"),
+        rows("1.2.3.5", "GET", "4321", null, "/history/voyager2/", null));
+  }
+
+  @Test
+  public void testCaseWhenWithIn() {
+    JSONObject actual =
+        executeQuery(
+            String.format(
+                """
+                    source=%s
+                    | eval status =
+                        case(
+                            response in ('200'), "Success",
+                            response in ('300', '301'), "Redirection",
+                            response in ('400', '403'), "Client Error",
+                            response in ('500', '505'), "Server Error"
+                            else concat("Incorrect HTTP status code for", url))
+                    | where status != "Success"
+                    """,
+                TEST_INDEX_WEBLOGS));
+    verifySchema(
+        actual,
+        schema("host", "ip"),
+        schema("method", "string"),
+        schema("url", "string"),
+        schema("response", "string"),
+        schema("bytes", "string"),
+        schema("status", "string"));
+    verifyDataRows(
+        actual,
+        rows("::1", "GET", "6245", "301", "/history/apollo/", "Redirection"),
+        rows(
+            "0.0.0.2",
+            "GET",
+            "4085",
+            "500",
+            "/shuttle/missions/sts-73/mission-sts-73.html",
+            "Server Error"),
+        rows("::3", "GET", "3985", "403", "/shuttle/countdown/countdown.html", "Client Error"),
+        rows(
+            "1.2.3.5",
+            "GET",
+            "4321",
+            null,
+            "/history/voyager2/",
+            "Incorrect HTTP status code for/history/voyager2/"));
+  }
+
+  @Test
+  public void testCaseWhenInFilter() {
+    JSONObject actual =
+        executeQuery(
+            String.format(
+                """
+                    source=%s
+                    | where not true =
+                        case(
+                            response in ('200'), true,
+                            response in ('300', '301'), false,
+                            response in ('400', '403'), false,
+                            response in ('500', '505'), false
+                            else false)
+                    """,
+                TEST_INDEX_WEBLOGS));
+    verifySchema(
+        actual,
+        schema("host", "ip"),
+        schema("method", "string"),
+        schema("url", "string"),
+        schema("response", "string"),
+        schema("bytes", "string"));
+    verifyDataRows(
+        actual,
+        rows("::1", "GET", "6245", "301", "/history/apollo/"),
+        rows("0.0.0.2", "GET", "4085", "500", "/shuttle/missions/sts-73/mission-sts-73.html"),
+        rows("::3", "GET", "3985", "403", "/shuttle/countdown/countdown.html"),
+        rows("1.2.3.5", "GET", "4321", null, "/history/voyager2/"));
+  }
+
+  @Test
+  public void testCaseWhenInSubquery() {
+    JSONObject actual =
+        executeQuery(
+            String.format(
+                """
+                    source=%s
+                    | where response in [
+                        source = %s
+                        | eval new_response = case(
+                            response in ('200'), "201",
+                            response in ('300', '301'), "301",
+                            response in ('400', '403'), "403",
+                            response in ('500', '505'), "500"
+                            else concat("Incorrect HTTP status code for", url))
+                        | fields new_response
+                      ]
+                    """,
+                TEST_INDEX_WEBLOGS, TEST_INDEX_WEBLOGS));
+    verifySchema(
+        actual,
+        schema("host", "ip"),
+        schema("method", "string"),
+        schema("url", "string"),
+        schema("response", "string"),
+        schema("bytes", "string"));
+    verifyDataRows(
+        actual,
+        rows("::1", "GET", "6245", "301", "/history/apollo/"),
+        rows("0.0.0.2", "GET", "4085", "500", "/shuttle/missions/sts-73/mission-sts-73.html"),
+        rows("::3", "GET", "3985", "403", "/shuttle/countdown/countdown.html"));
+  }
+}