Apache Calcite 实现方言转换的代码

public class SqlDialect {BUILT_IN_OPERATORS_LIST: 支持的内置定义函数或者运算符（例如：abs and..）// 列 表的标识符String identifierQuoteString:    标识符的开始符号String identifierEndQuoteString: 标识符的结束符号String identifierEscapedQuote: （暂时没有弄明白这个在做什么，像是字符串中的转义符？）// 常量的标识符String literalQuoteString:    常量的开始符号String literalEndQuoteString: 常量的结束符号String literalEscapedQuote:（暂时没有弄明白这个在做什么，像是字符串中的转义符？）DatabaseProduct databaseProduct: 所属的数据库产品NullCollation nullCollation: 在进行排序查询式，空值的返回顺序RelDataTypeSystem dataTypeSystem: 数据类型// 和解析相关Casing unquotedCasing: 大小写转换Casing quotedCasing: 大小写转换boolean caseSensitive: 是否大小写敏感(列名 表明 函数名等)}

// 方法区（不同的数据源根据细节的不同实现自定义的复写方法）allowsAsconfigureParserconfigureParsercontainsNonAsciicreatedefaultNullDirectionemptyContextemulateJoinTypeForCrossJoinemulateNullDirectionemulateNullDirectionWithIsNullgetCalendarPolicygetCastSpecgetConformancegetDatabaseProductgetNullCollationgetProductgetQuotedCasinggetQuotinggetSingleRowTableNamegetTypeSystemgetUnquotedCasinghasImplicitTableAliasidentifierNeedsQuoteisCaseSensitivequoteIdentifierquoteIdentifierquoteIdentifierquoteStringLiteralquoteStringLiteralquoteStringLiteralUnicodequoteTimestampLiteralrequiresAliasForFromItemsrewriteSingleValueExprsupportsAggregateFunctionsupportsAliasedValuessupportsCharSetsupportsDataTypesupportsFunctionsupportsGroupByWithCubesupportsGroupByWithRollupsupportsImplicitTypeCoercionsupportsNestedAggregationssupportsOffsetFetchsupportsWindowFunctionsunparseCallunparseDateTimeLiteralunparseFetchUsingAnsiunparseFetchUsingLimitunparseLimitunparseOffsetunparseOffsetFetchunparseSqlDatetimeArithmeticunparseSqlIntervalLiteralunparseSqlIntervalQualifierunparseTopNunquoteStringLiteral

/** Returns SqlNode for type in "cast(column as type)", which might be  * different between databases by type name, precision etc.  *  * <p>If this method returns null, the cast will be omitted. In the default  * implementation, this is the case for the NULL type, and therefore  * {@code CAST(NULL AS <nulltype>)} is rendered as {@code NULL}. */  public SqlNode getCastSpec(RelDataType type)  这个方法就可以根据具体的数据源的数据类型进行转换，例如：  @Override public SqlNode getCastSpec(RelDataType type) {    switch (type.getSqlTypeName()) {    case VARCHAR:      // MySQL doesn't have a VARCHAR type, only CHAR.      int vcMaxPrecision = this.getTypeSystem().getMaxPrecision(SqlTypeName.CHAR);      int precision = type.getPrecision();      if (vcMaxPrecision > 0 && precision > vcMaxPrecision) {        precision = vcMaxPrecision;      }      return new SqlDataTypeSpec(          new SqlBasicTypeNameSpec(SqlTypeName.CHAR, precision, SqlParserPos.ZERO),          SqlParserPos.ZERO);    }    return super.getCastSpec(type);  }  就可以经Sql中的Cast语句Cast为特定的类型：  final String query = "select cast(/"product_id/" as varchar(50)), /"product_id/" "       + "from /"product/" ";   final String expected = "SELECT CAST(`product_id` AS CHAR(50)), `product_id`/n"       + "FROM `foodmart`.`product`";

// 解析过的SqlNodesqlNode.toSqlString(CalciteSqlDialect.DEFAULT).getSql();