Apache Calcite code for dialect conversion

public class SqlDialect {

BUILT_IN_OPERATORS_LIST: Supported built-in functions or operators (for example: abs and..)

// List identifiers String identifierQuoteString: The start symbol of the identifier String identifierEndQuoteString: The end symbol of the identifier String identifierEscapedQuote: (I don't understand what this is doing yet, like an escape character in a string?)

// Constant identifier String literalQuoteString: constant start symbol String literalEndQuoteString: constant end symbol String literalEscapedQuote: (I don't understand what this is doing yet, like an escape character in a string?)

DatabaseProduct databaseProduct: the database product it belongs toNullCollation nullCollation: the order in which null values ​​are returned when performing a sort queryRelDataTypeSystem dataTypeSystem: data type // related to parsingCasing unquotedCasing: case conversionCasing quotedCasing: case conversionboolean caseSensitive: whether it is case sensitive (column name indicates function name, etc.)
}

// Method area (different data sources implement custom replication methods based on different details)
allowsAs
configureParser
configureParser
containsNonAscii
create
defaultNullDirection
emptyContext
emulateJoinTypeForCrossJoin
emulateNullDirection
emulateNullDirectionWithIsNull
getCalendarPolicy
getCastSpec
getConformance
getDatabaseProduct
getNullCollation
getProduct
getQuotedCasing
getQuoting
getSingleRowTableName
getTypeSystem
getUnquotedCasing
hasImplicitTableAlias
identifierNeedsQuote
isCaseSensitive
quoteIdentifier
quoteIdentifier
quoteIdentifier
quoteStringLiteral
quoteStringLiteral
quoteStringLiteralUnicode
quoteTimestampLiteral
requiresAliasForFromItems
rewriteSingleValueExpr
supportsAggregateFunction
supportsAliasedValues
supportsCharSet
supportsDataType
supportsFunction
supportsGroupByWithCube
supportsGroupByWithRollup
supportsImplicitTypeCoercion
supportsNestedAggregations
supportsOffsetFetch
supportsWindowFunctions
unparseCall
unparseDateTimeLiteral
unparseFetchUsingAnsi
unparseFetchUsingLimit
unparseLimit
unparseOffset
unparseOffsetFetch
unparseSqlDatetimeArithmetic
unparseSqlIntervalLiteral
unparseSqlIntervalQualifier
unparseTopN
unquoteStringLiteral

/** 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)

  This method can be used to convert data according to the data type of the specific data source, for example:

  @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);
  }

  You can use the Cast statement in SQL to cast it to a specific type:

  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`";

// Parsed SqlNode
sqlNode.toSqlString(CalciteSqlDialect.DEFAULT).getSql();