SQL: Fix querying of indices without columns (#74312) (#74466)

Fixes #53001

Adds support for querying indices without columns. Previously, such queries failed.

(cherry picked from commit 6f93303)

Author: Lukas Wegmann

x-pack/plugin/sql/qa/jdbc/src/main/java/org/elasticsearch/xpack/sql/qa/jdbc/JdbcErrorsTestCase.java

@@ -40,18 +40,6 @@ public void testSelectColumnFromMissingIndex() throws SQLException {
         }
     }
 
-    public void testSelectFromEmptyIndex() throws IOException, SQLException {
-        // Create an index without any types
-        Request request = new Request("PUT", "/test");
-        request.setJsonEntity("{}");
-        client().performRequest(request);
-
-        try (Connection c = esJdbc()) {
-            SQLException e = expectThrows(SQLException.class, () -> c.prepareStatement("SELECT * FROM test").executeQuery());
-            assertEquals("Found 1 problem\nline 1:8: Cannot determine columns for [*]", e.getMessage());
-        }
-    }
-
     public void testSelectColumnFromEmptyIndex() throws IOException, SQLException {
         Request request = new Request("PUT", "/test");
         request.setJsonEntity("{}");

x-pack/plugin/sql/qa/server/src/main/java/org/elasticsearch/xpack/sql/qa/ErrorsTestCase.java

@@ -18,8 +18,6 @@ public interface ErrorsTestCase {
 
     void testSelectColumnFromMissingIndex() throws Exception;
 
-    void testSelectFromEmptyIndex() throws Exception;
-
     void testSelectColumnFromEmptyIndex() throws Exception;
 
     void testSelectMissingField() throws Exception;

x-pack/plugin/sql/qa/server/src/main/java/org/elasticsearch/xpack/sql/qa/cli/ErrorsTestCase.java

@@ -43,17 +43,6 @@ public void testSelectColumnFromMissingIndex() throws Exception {
         assertEquals("line 1:17: Unknown index [test]" + END, readLine());
     }
 
-    @Override
-    public void testSelectFromEmptyIndex() throws Exception {
-        // Create an index without any types
-        Request request = new Request("PUT", "/test");
-        request.setJsonEntity("{}");
-        client().performRequest(request);
-
-        assertFoundOneProblem(command("SELECT * FROM test"));
-        assertEquals("line 1:8: Cannot determine columns for [*]" + END, readLine());
-    }
-
     @Override
     public void testSelectColumnFromEmptyIndex() throws Exception {
         Request request = new Request("PUT", "/test");

x-pack/plugin/sql/qa/server/src/main/java/org/elasticsearch/xpack/sql/qa/jdbc/DataLoader.java

@@ -72,6 +72,15 @@ protected static void loadEmpDatasetIntoEs(RestClient client) throws Exception {
         // frozen index
         loadEmpDatasetIntoEs(client, "frozen_emp", "employees");
         freeze(client, "frozen_emp");
+        loadNoColsDatasetIntoEs(client, "empty_mapping");
+    }
+
+    private static void loadNoColsDatasetIntoEs(RestClient client, String index) throws Exception {
+        createEmptyIndex(client, index);
+        Request request = new Request("POST", "/" + index + "/_bulk");
+        request.addParameter("refresh", "true");
+        request.setJsonEntity("{\"index\":{}\n{}\n" + "{\"index\":{}\n{}\n");
+        client.performRequest(request);
     }
 
     public static void loadDocsDatasetIntoEs(RestClient client) throws Exception {

x-pack/plugin/sql/qa/server/src/main/java/org/elasticsearch/xpack/sql/qa/jdbc/SqlSpecTestCase.java

@@ -32,7 +32,10 @@ public abstract class SqlSpecTestCase extends SpecBaseIntegrationTestCase {
     private String query;
 
     @ClassRule
-    public static LocalH2 H2 = new LocalH2(c -> c.createStatement().execute("RUNSCRIPT FROM 'classpath:/setup_test_emp.sql'"));
+    public static LocalH2 H2 = new LocalH2((c) -> {
+        c.createStatement().execute("RUNSCRIPT FROM 'classpath:/setup_test_emp.sql'");
+        c.createStatement().execute("RUNSCRIPT FROM 'classpath:/setup_empty_mapping.sql'");
+    });
 
     @ParametersFactory(argumentFormatting = PARAM_FORMATTING)
     public static List<Object[]> readScriptSpec() throws Exception {

x-pack/plugin/sql/qa/server/src/main/java/org/elasticsearch/xpack/sql/qa/rest/RestSqlTestCase.java

@@ -344,16 +344,6 @@ public void testSelectColumnFromMissingIndex() throws Exception {
         expectBadRequest(() -> runSql(mode, "SELECT abc FROM missing"), containsString("1:17: Unknown index [missing]"));
     }
 
-    @Override
-    public void testSelectFromEmptyIndex() throws Exception {
-        // Create an index without any types
-        Request request = new Request("PUT", "/test");
-        request.setJsonEntity("{}");
-        client().performRequest(request);
-        String mode = randomFrom("jdbc", "plain");
-        expectBadRequest(() -> runSql(mode, "SELECT * FROM test"), containsString("1:8: Cannot determine columns for [*]"));
-    }
-
     @Override
     public void testSelectColumnFromEmptyIndex() throws Exception {
         Request request = new Request("PUT", "/test");

x-pack/plugin/sql/qa/server/src/main/resources/command.csv-spec

@@ -223,13 +223,14 @@ TODAY          |SCALAR
 showTables
 SHOW TABLES;
 
-       name    |  type |  kind   
+       name    |  type |  kind
+empty_mapping  |TABLE  |INDEX
 logs           |TABLE  |INDEX
 logs_nanos     |TABLE  |INDEX
 test_alias     |VIEW   |ALIAS
-test_alias_emp |VIEW   |ALIAS 
-test_emp       |TABLE  |INDEX  
-test_emp_copy  |TABLE  |INDEX  
+test_alias_emp |VIEW   |ALIAS
+test_emp       |TABLE  |INDEX
+test_emp_copy  |TABLE  |INDEX
 ;
 
 showTablesSimpleLike
@@ -382,3 +383,19 @@ last_name           |VARCHAR        |text
 last_name.keyword   |VARCHAR        |keyword
 salary              |INTEGER        |integer
 ;
+
+
+describeNoCols
+DESCRIBE "empty_mapping";
+
+        column:s      |     type:s    |    mapping:s
+----------------------+---------------+---------------
+;
+
+
+showColumnsInNoCols
+SHOW COLUMNS IN "empty_mapping";
+
+        column:s      |     type:s    |    mapping:s
+----------------------+---------------+---------------
+;

x-pack/plugin/sql/qa/server/src/main/resources/empty-mapping.csv-spec

@@ -0,0 +1,28 @@
+
+// the following queries all return no rows in H2
+
+selectConstAggregationWithGroupBy
+SELECT 1 a, COUNT(*) b, MAX(1) c FROM empty_mapping GROUP BY a;
+
+       a:i     |       b:l     |       c:i
+---------------+---------------+---------------
+1              |2              |1
+;
+
+subselectWithConst
+SELECT 1, * FROM (SELECT * FROM empty_mapping) s;
+
+       1:i
+---------------
+1
+1
+;
+
+subselectWithInnerConst
+SELECT * FROM (SELECT 1, * FROM empty_mapping) s;
+
+       1:i
+---------------
+1
+1
+;

x-pack/plugin/sql/qa/server/src/main/resources/empty-mapping.sql-spec

@@ -0,0 +1,22 @@
+selectStar
+SELECT * FROM empty_mapping;
+selectStarWithFilter
+SELECT * FROM empty_mapping WHERE 2 > 1;
+selectStarWithFilterAndLimit
+SELECT * FROM empty_mapping WHERE 1 > 2 LIMIT 10;
+
+selectCount
+SELECT COUNT(*) FROM empty_mapping;
+// awaits fix: https://github.com/elastic/elasticsearch/issues/74311
+// selectCountWithWhere
+// SELECT COUNT(*) FROM empty_mapping WHERE 1 + 1 = 3;
+
+selectConst
+SELECT 1, 2, 3 FROM empty_mapping;
+selectConstAggregation
+SELECT MAX(1), SUM(2) FROM empty_mapping;
+
+// fails in H2 with a syntax error but cannot be tested in CSV spec because datasets without columns cannot be parsed
+// awaits fix: https://github.com/elastic/elasticsearch/issues/39895 (latest H2 version can run the query)
+// subselect
+// SELECT * FROM (SELECT * FROM empty_mapping) s;

x-pack/plugin/sql/qa/server/src/main/resources/setup_empty_mapping.sql

@@ -0,0 +1,5 @@
+DROP TABLE IF EXISTS "empty_mapping";
+CREATE TABLE "empty_mapping" ();
+
+INSERT INTO "empty_mapping" DEFAULT VALUES;
+INSERT INTO "empty_mapping" DEFAULT VALUES;