TAJO-2160: Implement string_agg function.

tajo-core-tests/src/test/java/org/apache/tajo/engine/function/TestBuiltinFunctions.java

@@ -748,4 +748,33 @@ public void testCorr() throws Exception {
       executeString("DROP TABLE testbuiltin11 PURGE");
     }
   }
+
+  @Test
+  public void testStringAgg() throws Exception {
+    Schema schema = SchemaBuilder.builder()
+        .add("id", TajoDataTypes.Type.INT4)
+        .add("value", TajoDataTypes.Type.TEXT)
+        .build();
+    String[] data = new String[]{
+        "1|\\N",
+        "1|a",
+        "1|b",
+        "1|c",
+        "2|d",
+        "2|f"};
+    TajoTestingCluster.createTable(conf, "testbuiltin11", schema, data, 1);
+
+    try {
+      ResultSet res = executeString("select string_agg(value, '|') as value from testbuiltin11 group by id order by id");
+      String ascExpected = "value\n" +
+          "-------------------------------\n" +
+          "null|a|b|c\n" +
+          "d|f\n";
+
+      assertEquals(ascExpected, resultSetToString(res));
+      res.close();
+    } finally {
+      executeString("DROP TABLE testbuiltin11 PURGE");
+    }
+  }
 }

tajo-core/src/main/java/org/apache/tajo/engine/function/builtin/StringAgg.java

@@ -0,0 +1,132 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.tajo.engine.function.builtin;
+
+import org.apache.commons.lang.StringEscapeUtils;
+import org.apache.tajo.InternalTypes.StringAggProto;
+import org.apache.tajo.catalog.CatalogUtil;
+import org.apache.tajo.catalog.Column;
+import org.apache.tajo.common.TajoDataTypes.DataType;
+import org.apache.tajo.common.TajoDataTypes.Type;
+import org.apache.tajo.datum.Datum;
+import org.apache.tajo.datum.DatumFactory;
+import org.apache.tajo.datum.NullDatum;
+import org.apache.tajo.datum.ProtobufDatum;
+import org.apache.tajo.engine.function.annotation.Description;
+import org.apache.tajo.engine.function.annotation.ParamTypes;
+import org.apache.tajo.plan.function.AggFunction;
+import org.apache.tajo.plan.function.FunctionContext;
+import org.apache.tajo.storage.Tuple;
+
+/**
+ * Function definition
+ *
+ * TEXT string_agg(expr TEXT, delimiter TEXT)
+ */
+@Description(
+  functionName = "string_agg",
+  description = "input values concatenated into a string, separated by delimiter",
+  example = "> SELECT string_agg(expr, delimiter);",
+  returnType = Type.TEXT,
+  paramTypes = { @ParamTypes(paramTypes = { Type.TEXT, Type.TEXT }) }
+)
+public class StringAgg extends AggFunction<Datum> {
+
+  public StringAgg() {
+    super(new Column[] {
+      new Column("expr", Type.TEXT),
+      new Column("delimiter", Type.TEXT)
+    });
+  }
+
+  @Override
+  public FunctionContext newContext() {
+    return new ConcatContext();
+  }
+
+  @Override
+  public void eval(FunctionContext ctx, Tuple params) {
+    ConcatContext concatCtx = (ConcatContext) ctx;
+
+    String concatData = null;
+    if (!params.isBlankOrNull(0)) {
+      concatData = params.getText(0);
+    }
+
+    if (concatCtx.concatData.length() > 0) {
+      concatCtx.concatData.append(concatCtx.delimiter);
+    } else {
+      // When first time, set the delimiter.
+      concatCtx.delimiter = StringEscapeUtils.unescapeJava(params.getText(1));
+    }
+    concatCtx.concatData.append(concatData);
+  }
+
+  @Override
+  public void merge(FunctionContext context, Tuple part) {
+    ConcatContext concatCtx = (ConcatContext) context;
+    if (part.isBlankOrNull(0)) {
+      return;
+    }
+
+    ProtobufDatum datum = (ProtobufDatum) part.getProtobufDatum(0);
+    StringAggProto proto = (StringAggProto) datum.get();
+
+    String delimiter = proto.getDelimiter();
+    String concatData = proto.getValue();
+
+    if (concatCtx.concatData.length() > 0) {
+      concatCtx.concatData.append(delimiter);
+    }
+    concatCtx.concatData.append(concatData);
+  }
+
+  @Override
+  public Datum getPartialResult(FunctionContext ctx) {
+    ConcatContext concatCtx = (ConcatContext) ctx;
+    if (concatCtx.concatData.length() == 0) {
+      return NullDatum.get();
+    }
+
+    StringAggProto.Builder builder = StringAggProto.newBuilder();
+    builder.setDelimiter(concatCtx.delimiter);
+    builder.setValue(concatCtx.concatData.toString());
+    return new ProtobufDatum(builder.build());
+  }
+
+  @Override
+  public DataType getPartialResultType() {
+    return CatalogUtil.newDataType(Type.PROTOBUF, StringAggProto.class.getName());
+  }
+
+  @Override
+  public Datum terminate(FunctionContext ctx) {
+    ConcatContext concatCtx = (ConcatContext) ctx;
+    if (concatCtx.concatData.length() == 0) {
+      return NullDatum.get();
+    } else {
+      return DatumFactory.createText(concatCtx.concatData.toString());
+    }
+  }
+
+  protected static class ConcatContext implements FunctionContext {
+    String delimiter;
+    StringBuilder concatData = new StringBuilder(128);
+  }
+}

tajo-core/src/main/proto/InternalTypes.proto

@@ -45,3 +45,8 @@ message CorrProto {
   required double yvar = 5;
   required double covar = 6;
 }
+
+message StringAggProto {
+  required string value = 1;
+  required string delimiter = 2;
+}