use set

package io.shardingsphere.core.parsing.parser.clause;

import java.util.Collection;

import java.util.Collections;

import java.util.LinkedList;

import java.util.List;

import java.util.regex.Matcher;

import java.util.regex.Pattern;

import com.google.common.base.Optional;

import io.shardingsphere.core.constant.AggregationType;

import io.shardingsphere.core.parsing.lexer.LexerEngine;

import io.shardingsphere.core.parsing.lexer.token.DefaultKeyword;

import io.shardingsphere.core.util.SQLUtil;

import lombok.Getter;

import java.util.Collection;

import java.util.Collections;

import java.util.LinkedList;

import java.util.List;

import java.util.regex.Matcher;

import java.util.regex.Pattern;

/**

 * Select list clause parser.

 *

        lexerEngine.nextToken();

        String distinctColumnName = lexerEngine.getCurrentToken().getLiterals();

        if (Symbol.STAR == lexerEngine.getCurrentToken().getType()) {

            return new DistinctSelectItem(Collections.<String>emptyList(), aliasExpressionParser.parseSelectItemAlias());

            return new DistinctSelectItem(Collections.<String>emptySet(), aliasExpressionParser.parseSelectItemAlias());

        }

        lexerEngine.nextToken();

        distinctColumnName = SQLUtil.getExactlyValue(distinctColumnName + parseRestSelectItem(selectStatement));

        return new DistinctSelectItem(Collections.singletonList(distinctColumnName), aliasExpressionParser.parseSelectItemAlias());

        return new DistinctSelectItem(Collections.singleton(distinctColumnName), aliasExpressionParser.parseSelectItemAlias());

    }

    private boolean isStarSelectItem() {