/*
 * 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.HashSet;
import java.util.Set;

/**
 * Distinct select item.
 *
 * @author panjuan
 */
@Getter
@EqualsAndHashCode
@ToString
public final class DistinctSelectItem implements SelectItem {
    
    private final Set<String> distinctColumnNames = new HashSet<>();
    
    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 distinctColumnNames.isEmpty() ? DefaultKeyword.DISTINCT.name() : SQLUtil.getExactlyValue(DefaultKeyword.DISTINCT + " " + Joiner.on(", ").join(distinctColumnNames));
    }
    
    /**
     * Get column label.
     *
     * @return column label
     */
    public String getColumnLabel() {
        return alias.isPresent() ? alias.get() : getExpression();
    }
}

@@ -994,23 +994,27 @@
 va.util.
-HashSet
+Collections
 ;%0Aimport
@@ -1024,18 +1024,48 @@
 va.util.
-Se
+LinkedList;%0Aimport java.util.Lis
 t;%0A%0A/**%0A
@@ -1237,18 +1237,19 @@
 e final 
-Se
+Lis
 t%3CString
@@ -1280,14 +1280,17 @@
 new 
-HashSe
+LinkedLis
 t%3C%3E(
@@ -1908,24 +1908,24 @@
 mnLabel() %7B%0A
-
         retu
@@ -1984,10 +1984,590 @@
 ;%0A    %7D%0A
+    %0A    /**%0A     * Get distinct column labels.%0A     *%0A     * @return distinct column labels%0A     */%0A    public Collection%3CString%3E getDistinctColumnLabels() %7B%0A        return alias.isPresent() ? getDistinctColumnLabels(alias.get()) : distinctColumnNames;%0A    %7D%0A    %0A    private Collection%3CString%3E getDistinctColumnLabels(final String alias) %7B%0A        if (1 == distinctColumnNames.size()) %7B%0A            return Collections.singletonList(alias);%0A        %7D%0A        List%3CString%3E result = new LinkedList%3C%3E(distinctColumnNames);%0A        result.set(0, alias);%0A        return result;%0A    %7D%0A
 %7D%0A

add getDistinctColumnLabels()