/*
 * Copyright 2016-2018 shardingsphere.io.
 * <p>
 * Licensed 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.
 * </p>
 */

package io.shardingsphere.core.parsing.parser.context.selectitem;

import com.google.common.base.Joiner;
import com.google.common.base.Optional;
import io.shardingsphere.core.parsing.lexer.token.DefaultKeyword;
import io.shardingsphere.core.util.SQLUtil;
import lombok.EqualsAndHashCode;
import lombok.Getter;
import lombok.ToString;

import java.util.Collection;
import java.util.Collections;
import java.util.LinkedList;
import java.util.List;

/**
 * Distinct select item.
 *
 * @author panjuan
 */
@Getter
@EqualsAndHashCode
@ToString
public final class DistinctSelectItem implements SelectItem {
    
    private final List<String> distinctColumnNames = new LinkedList<>();
    private final Optional<String> alias;
    
    public DistinctSelectItem(final Collection<String> distinctColumnNames, final Optional<String> alias) {
        this.distinctColumnNames.addAll(distinctColumnNames);
        this.alias = alias;
    }
    
    @Override
    public String getExpression() {
        return isSingleColumnWithAlias() ? DefaultKeyword.DISTINCT.name() + " " + distinctColumnNames.get(0) + "AS" + alias.get() 
                : SQLUtil.getExactlyValue(DefaultKeyword.DISTINCT + " " + Joiner.on(", ").join(distinctColumnNames));
    }
    
    /**
     * Get distinct column labels.
     *
     * @return distinct column labels
     */
    public Collection<String> getDistinctColumnLabels() {
        return isSingleColumnWithAlias() ? Collections.singletonList(alias.get()) : distinctColumnNames;
    }
    
    private boolean isSingleColumnWithAlias() {
        return 1 == distinctColumnNames.size() && alias.isPresent();
    }
}

@@ -919,24 +919,63 @@
 bok.Getter;%0A
+import lombok.RequiredArgsConstructor;%0A
 import lombo
@@ -1067,40 +1067,10 @@
 til.
-LinkedList;%0Aimport java.util.Lis
+Se
 t;%0A%0A
@@ -1124,16 +1124,41 @@
 uan%0A */%0A
+@RequiredArgsConstructor%0A
 @Getter%0A
@@ -1271,19 +1271,18 @@
 e final 
-Lis
+Se
 t%3CString
@@ -1306,281 +1306,56 @@
 ames
- = new LinkedList%3C%3E();%0A    private final Optional%3CString%3E alias;%0A    %0A    public DistinctSelectItem(final Collection%3CString%3E distinctColumnNames, final Optional%3CString%3E alias) %7B%0A        this.distinctColumnNames.addAll(distinctColumnNames);%0A        this.alias = alias;%0A    %7D
+;%0A    %0A    private final Optional%3CString%3E alias;
 %0A   
@@ -1449,16 +1449,40 @@
 ias() ? 
+SQLUtil.getExactlyValue(
 DefaultK
@@ -1536,13 +1536,24 @@
 mes.
-ge
+iterator().nex
 t(
-0
 ) + 
@@ -1570,16 +1570,17 @@
 as.get()
+)
  %0A      

use SQLUtil