ApacheCalcite实现方言转换的代码

定义

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实现

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. * *

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 )} 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();

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