PPL describe command (#646)

Signed-off-by: Sean Kao <seankao@amazon.com>

docs/category.json

@@ -8,6 +8,7 @@
   ],
   "ppl_cli": [
     "user/ppl/cmd/dedup.rst",
+    "user/ppl/cmd/describe.rst",
     "user/ppl/cmd/eval.rst",
     "user/ppl/cmd/fields.rst",
     "user/ppl/cmd/head.rst",

docs/user/ppl/cmd/describe.rst

@@ -0,0 +1,65 @@
+=============
+describe
+=============
+
+.. rubric:: Table of contents
+
+.. contents::
+   :local:
+   :depth: 2
+
+
+Description
+============
+| Using ``describe`` command to query metadata of the index. ``describe`` command could be only used as the first command in the PPL query.
+
+
+Syntax
+============
+describe <index>
+
+* index: mandatory. describe command must specify which index to query from.
+
+
+Example 1: Fetch all the metadata
+=================================
+
+The example describes accounts index.
+
+PPL query::
+
+    os> describe accounts;
+    fetched rows / total rows = 11/11
+    +----------------+---------------+--------------+----------------+-------------+-------------+---------------+-----------------+------------------+------------------+------------+-----------+--------------+-----------------+--------------------+---------------------+--------------------+---------------+-----------------+----------------+---------------+--------------------+--------------------+----------------------+
+    | TABLE_CAT      | TABLE_SCHEM   | TABLE_NAME   | COLUMN_NAME    | DATA_TYPE   | TYPE_NAME   | COLUMN_SIZE   | BUFFER_LENGTH   | DECIMAL_DIGITS   | NUM_PREC_RADIX   | NULLABLE   | REMARKS   | COLUMN_DEF   | SQL_DATA_TYPE   | SQL_DATETIME_SUB   | CHAR_OCTET_LENGTH   | ORDINAL_POSITION   | IS_NULLABLE   | SCOPE_CATALOG   | SCOPE_SCHEMA   | SCOPE_TABLE   | SOURCE_DATA_TYPE   | IS_AUTOINCREMENT   | IS_GENERATEDCOLUMN   |
+    |----------------+---------------+--------------+----------------+-------------+-------------+---------------+-----------------+------------------+------------------+------------+-----------+--------------+-----------------+--------------------+---------------------+--------------------+---------------+-----------------+----------------+---------------+--------------------+--------------------+----------------------|
+    | docTestCluster | null          | accounts     | account_number | null        | long        | null          | null            | null             | 10               | 2          | null      | null         | null            | null               | null                | 0                  |               | null            | null           | null          | null               | NO                 |                      |
+    | docTestCluster | null          | accounts     | firstname      | null        | text        | null          | null            | null             | 10               | 2          | null      | null         | null            | null               | null                | 1                  |               | null            | null           | null          | null               | NO                 |                      |
+    | docTestCluster | null          | accounts     | address        | null        | text        | null          | null            | null             | 10               | 2          | null      | null         | null            | null               | null                | 2                  |               | null            | null           | null          | null               | NO                 |                      |
+    | docTestCluster | null          | accounts     | balance        | null        | long        | null          | null            | null             | 10               | 2          | null      | null         | null            | null               | null                | 3                  |               | null            | null           | null          | null               | NO                 |                      |
+    | docTestCluster | null          | accounts     | gender         | null        | text        | null          | null            | null             | 10               | 2          | null      | null         | null            | null               | null                | 4                  |               | null            | null           | null          | null               | NO                 |                      |
+    | docTestCluster | null          | accounts     | city           | null        | text        | null          | null            | null             | 10               | 2          | null      | null         | null            | null               | null                | 5                  |               | null            | null           | null          | null               | NO                 |                      |
+    | docTestCluster | null          | accounts     | employer       | null        | text        | null          | null            | null             | 10               | 2          | null      | null         | null            | null               | null                | 6                  |               | null            | null           | null          | null               | NO                 |                      |
+    | docTestCluster | null          | accounts     | state          | null        | text        | null          | null            | null             | 10               | 2          | null      | null         | null            | null               | null                | 7                  |               | null            | null           | null          | null               | NO                 |                      |
+    | docTestCluster | null          | accounts     | age            | null        | long        | null          | null            | null             | 10               | 2          | null      | null         | null            | null               | null                | 8                  |               | null            | null           | null          | null               | NO                 |                      |
+    | docTestCluster | null          | accounts     | email          | null        | text        | null          | null            | null             | 10               | 2          | null      | null         | null            | null               | null                | 9                  |               | null            | null           | null          | null               | NO                 |                      |
+    | docTestCluster | null          | accounts     | lastname       | null        | text        | null          | null            | null             | 10               | 2          | null      | null         | null            | null               | null                | 10                 |               | null            | null           | null          | null               | NO                 |                      |
+    +----------------+---------------+--------------+----------------+-------------+-------------+---------------+-----------------+------------------+------------------+------------+-----------+--------------+-----------------+--------------------+---------------------+--------------------+---------------+-----------------+----------------+---------------+--------------------+--------------------+----------------------+
+
+Example 2: Fetch metadata with condition and filter
+===================================================
+
+The example retrieves columns with type long in accounts index.
+
+PPL query::
+
+    os> describe accounts | where TYPE_NAME="long" | fields COLUMN_NAME;
+    fetched rows / total rows = 3/3
+    +----------------+
+    | COLUMN_NAME    |
+    |----------------|
+    | account_number |
+    | balance        |
+    | age            |
+    +----------------+
+

docs/user/ppl/cmd/syntax.rst

@@ -10,7 +10,7 @@ Syntax
 
 Command Order
 =============
-The PPL query started with ``search`` command to reference a table search from. All the following command could be in any order. In the following example, ``search`` command refer the accounts index as the source, then using fields and where command to do the further processing.
+The PPL query starts with either the ``search`` command to reference a table to search from, or the ``describe`` command to reference a table to get its metadata. All the following command could be in any order. In the following example, ``search`` command refer the accounts index as the source, then using fields and where command to do the further processing.
 
 .. code-block::
 

docs/user/ppl/index.rst

@@ -40,6 +40,8 @@ The query start with search command and then flowing a set of command delimited
 
   - `dedup command <cmd/dedup.rst>`_
 
+  - `describe command <cmd/describe.rst>`_
+
   - `eval command <cmd/eval.rst>`_
 
   - `fields command <cmd/fields.rst>`_

integ-test/src/test/java/org/opensearch/sql/ppl/DescribeCommandIT.java

@@ -0,0 +1,90 @@
+/*
+ * Copyright OpenSearch Contributors
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+
+package org.opensearch.sql.ppl;
+
+import org.json.JSONObject;
+import org.junit.jupiter.api.Test;
+import org.opensearch.client.Request;
+import org.opensearch.client.ResponseException;
+
+import java.io.IOException;
+
+import static org.opensearch.sql.legacy.TestsConstants.TEST_INDEX_DOG;
+import static org.opensearch.sql.util.MatcherUtils.columnName;
+import static org.opensearch.sql.util.MatcherUtils.verifyColumn;
+import static org.opensearch.sql.util.MatcherUtils.verifyDataRows;
+
+public class DescribeCommandIT extends PPLIntegTestCase {
+
+  @Override
+  public void init() throws IOException {
+    loadIndex(Index.DOG);
+  }
+
+  @Test
+  public void testDescribeAllFields() throws IOException {
+    JSONObject result = executeQuery(String.format("describe %s", TEST_INDEX_DOG));
+    verifyColumn(
+        result,
+        columnName("TABLE_CAT"),
+        columnName("TABLE_SCHEM"),
+        columnName("TABLE_NAME"),
+        columnName("COLUMN_NAME"),
+        columnName("DATA_TYPE"),
+        columnName("TYPE_NAME"),
+        columnName("COLUMN_SIZE"),
+        columnName("BUFFER_LENGTH"),
+        columnName("DECIMAL_DIGITS"),
+        columnName("NUM_PREC_RADIX"),
+        columnName("NULLABLE"),
+        columnName("REMARKS"),
+        columnName("COLUMN_DEF"),
+        columnName("SQL_DATA_TYPE"),
+        columnName("SQL_DATETIME_SUB"),
+        columnName("CHAR_OCTET_LENGTH"),
+        columnName("ORDINAL_POSITION"),
+        columnName("IS_NULLABLE"),
+        columnName("SCOPE_CATALOG"),
+        columnName("SCOPE_SCHEMA"),
+        columnName("SCOPE_TABLE"),
+        columnName("SOURCE_DATA_TYPE"),
+        columnName("IS_AUTOINCREMENT"),
+        columnName("IS_GENERATEDCOLUMN")
+    );
+  }
+
+  @Test
+  public void testDescribeFilterFields() throws IOException {
+    JSONObject result = executeQuery(String.format("describe %s | fields TABLE_NAME, COLUMN_NAME, TYPE_NAME", TEST_INDEX_DOG));
+    verifyColumn(
+        result,
+        columnName("TABLE_NAME"),
+        columnName("COLUMN_NAME"),
+        columnName("TYPE_NAME")
+    );
+  }
+
+  @Test
+  public void testDescribeWithSpecialIndexName() throws IOException {
+    executeRequest(new Request("PUT", "/logs-2021.01.11"));
+    verifyDataRows(executeQuery("describe logs-2021.01.11"));
+
+    executeRequest(new Request("PUT", "/logs-7.10.0-2021.01.11"));
+    verifyDataRows(executeQuery("describe logs-7.10.0-2021.01.11"));
+  }
+
+  @Test
+  public void describeCommandWithoutIndexShouldFailToParse() throws IOException {
+    try {
+      executeQuery("describe");
+      fail();
+    } catch (ResponseException e) {
+      assertTrue(e.getMessage().contains("RuntimeException"));
+      assertTrue(e.getMessage().contains("Failed to parse query due to offending symbol"));
+    }
+  }
+}

ppl/src/main/antlr/OpenSearchPPLLexer.g4

@@ -11,6 +11,7 @@ channels { WHITESPACE, ERRORCHANNEL }
 
 // COMMAND KEYWORDS
 SEARCH:                             'SEARCH';
+DESCRIBE:                           'DESCRIBE';
 FROM:                               'FROM';
 WHERE:                              'WHERE';
 FIELDS:                             'FIELDS';

ppl/src/main/antlr/OpenSearchPPLParser.g4

@@ -14,10 +14,15 @@ root
 
 /** statement */
 pplStatement
-    : searchCommand (PIPE commands)*
+    : pplCommands (PIPE commands)*
     ;
 
 /** commands */
+pplCommands
+    : searchCommand
+    | describeCommand
+    ;
+
 commands
     : whereCommand | fieldsCommand | renameCommand | statsCommand | dedupCommand | sortCommand | evalCommand | headCommand
     | topCommand | rareCommand | parseCommand | kmeansCommand | adCommand;
@@ -28,6 +33,10 @@ searchCommand
     | (SEARCH)? logicalExpression fromClause                        #searchFilterFrom
     ;
 
+describeCommand
+    : DESCRIBE tableSourceClause
+    ;
+
 whereCommand
     : WHERE logicalExpression
     ;
@@ -119,8 +128,12 @@ adParameter
 
 /** clauses */
 fromClause
-    : SOURCE EQUAL tableSource (COMMA tableSource)*
-    | INDEX EQUAL tableSource (COMMA tableSource)*
+    : SOURCE EQUAL tableSourceClause
+    | INDEX EQUAL tableSourceClause
+    ;
+
+tableSourceClause
+    : tableSource (COMMA tableSource)*
     ;
 
 renameClasue

ppl/src/main/java/org/opensearch/sql/ppl/parser/AstBuilder.java

@@ -6,7 +6,9 @@
 
 package org.opensearch.sql.ppl.parser;
 
+import static org.opensearch.sql.ast.dsl.AstDSL.qualifiedName;
 import static org.opensearch.sql.ppl.antlr.parser.OpenSearchPPLParser.DedupCommandContext;
+import static org.opensearch.sql.ppl.antlr.parser.OpenSearchPPLParser.DescribeCommandContext;
 import static org.opensearch.sql.ppl.antlr.parser.OpenSearchPPLParser.EvalCommandContext;
 import static org.opensearch.sql.ppl.antlr.parser.OpenSearchPPLParser.FieldsCommandContext;
 import static org.opensearch.sql.ppl.antlr.parser.OpenSearchPPLParser.FromClauseContext;
@@ -19,8 +21,10 @@
 import static org.opensearch.sql.ppl.antlr.parser.OpenSearchPPLParser.SearchFromFilterContext;
 import static org.opensearch.sql.ppl.antlr.parser.OpenSearchPPLParser.SortCommandContext;
 import static org.opensearch.sql.ppl.antlr.parser.OpenSearchPPLParser.StatsCommandContext;
+import static org.opensearch.sql.ppl.antlr.parser.OpenSearchPPLParser.TableSourceClauseContext;
 import static org.opensearch.sql.ppl.antlr.parser.OpenSearchPPLParser.TopCommandContext;
 import static org.opensearch.sql.ppl.antlr.parser.OpenSearchPPLParser.WhereCommandContext;
+import static org.opensearch.sql.utils.SystemIndexUtils.mappingTable;
 
 import com.google.common.collect.ImmutableList;
 import com.google.common.collect.ImmutableMap;
@@ -79,11 +83,11 @@ public class AstBuilder extends OpenSearchPPLParserBaseVisitor<UnresolvedPlan> {
 
   @Override
   public UnresolvedPlan visitPplStatement(PplStatementContext ctx) {
-    UnresolvedPlan search = visit(ctx.searchCommand());
+    UnresolvedPlan pplCommand = visit(ctx.pplCommands());
     return ctx.commands()
         .stream()
         .map(this::visit)
-        .reduce(search, (r, e) -> e.attach(r));
+        .reduce(pplCommand, (r, e) -> e.attach(r));
   }
 
   /**
@@ -106,6 +110,15 @@ public UnresolvedPlan visitSearchFilterFrom(SearchFilterFromContext ctx) {
         visit(ctx.fromClause()));
   }
 
+  /**
+   * Describe command.
+   */
+  @Override
+  public UnresolvedPlan visitDescribeCommand(DescribeCommandContext ctx) {
+    final Relation table = (Relation) visitTableSourceClause(ctx.tableSourceClause());
+    return new Relation(qualifiedName(mappingTable(table.getTableName())));
+  }
+
   /**
    * Where command.
    */
@@ -286,6 +299,11 @@ public UnresolvedPlan visitTopCommand(TopCommandContext ctx) {
    */
   @Override
   public UnresolvedPlan visitFromClause(FromClauseContext ctx) {
+    return visitTableSourceClause(ctx.tableSourceClause());
+  }
+
+  @Override
+  public UnresolvedPlan visitTableSourceClause(TableSourceClauseContext ctx) {
     return new Relation(ctx.tableSource()
         .stream().map(this::internalVisitExpression)
         .collect(Collectors.toList()));

ppl/src/test/java/org/opensearch/sql/ppl/antlr/PPLSyntaxParserTest.java

@@ -145,5 +145,31 @@ public void can_parse_simple_query_string_relevance_function() {
         "SOURCE=test | WHERE simple_query_string([\"Tags\" ^ 1.5, Title, `Body` 4.2], 'query',"
             + "analyzer=keyword, quote_field_suffix=\".exact\", fuzzy_prefix_length = 4)"));
   }
+
+  @Test
+  public void testDescribeCommandShouldPass() {
+    ParseTree tree = new PPLSyntaxParser().analyzeSyntax("describe t");
+    assertNotEquals(null, tree);
+  }
+
+  @Test
+  public void testDescribeCommandWithMultipleIndicesShouldPass() {
+    ParseTree tree = new PPLSyntaxParser().analyzeSyntax("describe t,u");
+    assertNotEquals(null, tree);
+  }
+
+  @Test
+  public void testDescribeFieldsCommandShouldPass() {
+    ParseTree tree = new PPLSyntaxParser().analyzeSyntax("describe t | fields a,b");
+    assertNotEquals(null, tree);
+  }
+
+  @Test
+  public void testDescribeCommandWithSourceShouldFail() {
+    exceptionRule.expect(RuntimeException.class);
+    exceptionRule.expectMessage("Failed to parse query due to offending symbol");
+
+    new PPLSyntaxParser().analyzeSyntax("describe source=t");
+  }
 }