sharding不支持Union

今天写代码遇到一个错误：

com.dangdang.ddframe.rdb.sharding.parsing.parser.exception.SQLParsingUnsupportedException: Not supported token 'UNION'

com.dangdang.ddframe.rdb.sharding.parsing.parser.exception.SQLParsingUnsupportedException: Not supported token 'UNION'.
	at com.dangdang.ddframe.rdb.sharding.parsing.lexer.LexerEngine.unsupportedIfEqual(LexerEngine.java:173)
	at com.dangdang.ddframe.rdb.sharding.parsing.parser.clause.SelectRestClauseParser.parse(SelectRestClauseParser.java:29)
	at com.dangdang.ddframe.rdb.sharding.parsing.parser.sql.dql.select.AbstractSelectParser.parseSelectRest(AbstractSelectParser.java:129)
	at com.dangdang.ddframe.rdb.sharding.parsing.parser.dialect.mysql.sql.MySQLSelectParser.parseInternal(MySQLSelectParser.java:56)
	at com.dangdang.ddframe.rdb.sharding.parsing.parser.sql.dql.select.AbstractSelectParser.parseInternal(AbstractSelectParser.java:81)
	at com.dangdang.ddframe.rdb.sharding.parsing.parser.sql.dql.select.AbstractSelectParser.parse(AbstractSelectParser.java:68)
	at com.dangdang.ddframe.rdb.sharding.parsing.parser.sql.dql.select.AbstractSelectParser.parse(AbstractSelectParser.java:46)
	at com.dangdang.ddframe.rdb.sharding.parsing.SQLParsingEngine.parse(SQLParsingEngine.java:50)
	at com.dangdang.ddframe.rdb.sharding.routing.router.ParsingSQLRouter.parse(ParsingSQLRouter.java:71)
	at com.dangdang.ddframe.rdb.sharding.routing.PreparedStatementRoutingEngine.route(PreparedStatementRoutingEngine.java:55)
	at com.dangdang.ddframe.rdb.sharding.jdbc.core.statement.ShardingPreparedStatement.route(ShardingPreparedStatement.java:149)
	at com.dangdang.ddframe.rdb.sharding.jdbc.core.statement.ShardingPreparedStatement.executeQuery(ShardingPreparedStatement.java:114)

根据错误日志可以不支持union，不信邪跟了下sharding的源码，使用的版本是1.5.4，找到这个限制：

SelectRestClauseParser.java类中

 

public final void parse() {
        Collection unsupportedRestKeywords = new LinkedList<>();
        unsupportedRestKeywords.addAll(Arrays.asList(DefaultKeyword.UNION, DefaultKeyword.INTERSECT, DefaultKeyword.EXCEPT, DefaultKeyword.MINUS));
        unsupportedRestKeywords.addAll(Arrays.asList(getUnsupportedKeywordsRest()));
        lexerEngine.unsupportedIfEqual(unsupportedRestKeywords.toArray(new Keyword[unsupportedRestKeywords.size()]));
    }

由此可见，sharding不支持以上关键字。

后来又查了一些网上资料，确实有提出不支持union。