Added more query examples

Author: chernser

client-v2/src/main/java/com/clickhouse/client/api/Client.java

@@ -790,9 +790,10 @@ public CompletableFuture<Records> queryRecords(String sqlQuery, QuerySettings se
 
     /**
      * <p>Queries data in descriptive format and reads result to a collection.</p>
-     * <p>Use this method for queries that would return only a few records only.</p>
-     * @param sqlQuery
-     * @return
+     * <p>Use this method for queries that would return only a few records only because client
+     * will read whole dataset and convert it into a list of GenericRecord</p>
+     * @param sqlQuery - SQL query
+     * @return - complete list of records
      */
     public List<GenericRecord> queryAll(String sqlQuery) {
         try {
@@ -859,10 +860,18 @@ public String toString() {
                 '}';
     }
 
+    /**
+     * Returns unmodifiable map of configuration options.
+     * @return - configuration options
+     */
     public Map<String, String> getConfiguration() {
         return Collections.unmodifiableMap(configuration);
     }
 
+    /**
+     * Returns unmodifiable set of endpoints.
+     * @return - set of endpoints
+     */
     public Set<String> getEndpoints() {
         return Collections.unmodifiableSet(endpoints);
     }

examples/client-v2/src/main/java/com/clickhouse/examples/client_v2/SimpleReader.java

@@ -35,8 +35,6 @@ public class SimpleReader {
 
     Client client;
 
-    String database;
-
     public SimpleReader(String endpoint, String user, String password, String database) {
         // Create a lightweight object to interact with ClickHouse server
         Client.Builder clientBuilder = new Client.Builder()
@@ -47,7 +45,6 @@ public SimpleReader(String endpoint, String user, String password, String databa
                 .setDefaultDatabase(database);
 
         this.client = clientBuilder.build();
-        this.database = database;
     }
 
     public boolean isServerAlive() {
@@ -60,13 +57,17 @@ public void readDataUsingBinaryFormat() {
             log.info("Reading data from table: {}", TABLE_NAME);
 
             final String sql = "select * from " + TABLE_NAME + " where title <> '' limit 10";
+
             // Default format is RowBinaryWithNamesAndTypesFormatReader so reader have all information about columns
             QueryResponse response = client.query(sql).get(3, TimeUnit.SECONDS);
+
             // Create a reader to access the data in a convenient way
             ClickHouseBinaryFormatReader reader = new RowBinaryWithNamesAndTypesFormatReader(response.getInputStream());
 
             while (reader.hasNext()) {
-                reader.next();
+                reader.next(); // Read the next record from stream and parse it
+
+                // get values
                 double id = reader.getDouble("id");
                 String title = reader.getString("title");
                 String url = reader.getString("url");
@@ -84,6 +85,8 @@ public void readDataAll() {
         try {
             log.info("Reading whole table and process record by record");
             final String sql = "select * from " + TABLE_NAME + " where title <> ''";
+
+            // Read whole result set and process it record by record
             client.queryAll(sql).forEach(row -> {
                 double id = row.getDouble("id");
                 String title = row.getString("title");
@@ -102,6 +105,11 @@ public void readData() {
             final String sql = "select * from " + TABLE_NAME + " where title <> '' limit 10";
             Records records = client.queryRecords(sql).get(3, TimeUnit.SECONDS);
 
+            // Get some metrics
+            log.info("Data read successfully: {} ms", TimeUnit.NANOSECONDS.toMillis(records.getServerTime()));
+            log.info("Total rows: {}", records.getResultRows());
+
+            // Iterate thru records
             for (GenericRecord record : records) {
                 double id = record.getDouble("id");
                 String title = record.getString("title");