monetdb-java: src/main/java/nl/cwi/monetdb/jdbc/MonetDatabaseMetaData.java comparison

comparison src/main/java/nl/cwi/monetdb/jdbc/MonetDatabaseMetaData.java @ 15:6e48d0fae766

Corrected return values of DatabaseMetaData methods nullsAreSortedHigh(), nullsAreSortedLow(), getMaxCursorNameLength(), getMaxProcedureNameLength(), getMaxStatementLength() and getMaxUserNameLength(). Improved return values of DatabaseMetaData methods getMaxBinaryLiteralLength(), getMaxCharLiteralLength() and getMaxColumnsInTable().

author	Martin van Dinther <martin.van.dinther@monetdbsolutions.com>
date	Thu, 06 Oct 2016 19:44:34 +0200 (2016-10-06)
parents	b3ca1157be73
children	7acc09f59b21

comparison

equal deleted inserted replaced

-:3fa949cbc783
+:6e48d0fae766
 	public boolean isReadOnly() {
 		return false;
 	}
 	/**
-	 * Are NULL values sorted high?
+	 * Retrieves whether NULL values are sorted high. Sorted high means
-	 *
+	 * that NULL values sort higher than any other value in a domain.
-	 * @return true because MonetDB puts NULL values on top upon ORDER BY
+	 * In an ascending order, if this method returns true, NULL values will appear at the end.
+	 * By contrast, the method nullsAreSortedAtEnd indicates whether NULL values are sorted at the end regardless of sort order.
+	 *
+	 * @return false because MonetDB shows NULL values at the beginning upon ORDER BY .. ASC
 	 */
 	@Override
 	public boolean nullsAreSortedHigh() {
-		return true;
+		return false;
 	}
 	/**
-	 * Are NULL values sorted low?
+	 * Retrieves whether NULL values are sorted low. Sorted low means
+	 * that NULL values sort lower than any other value in a domain.
+	 * In an ascending order, if this method returns true, NULL values will appear at the beginning.
+	 * By contrast, the method nullsAreSortedAtStart indicates whether NULL values are sorted at the beginning regardless of sort order.
+	 *
+	 * @return true because MonetDB shows NULL values at the beginning upon ORDER BY .. ASC
 	 *
 	 * @return negative of nullsAreSortedHigh()
 	 * @see #nullsAreSortedHigh()
 	 */
 	@Override
 	public boolean nullsAreSortedLow() {
-		return !nullsAreSortedHigh();
+		return true;
 	}
 	/**
 	 * Are NULL values sorted at the start regardless of sort order?
 	 *
 	public int getDriverMinorVersion() {
 		return MonetDriver.getDriverMinorVersion();
 	}
 	/**
-	 * Does the database store tables in a local file?	No - it
+	 * Does the database store tables in a local file?
-	 * stores them in a file on the server.
+	 * No, it stores them in files on the server.
 	 *
 	 * @return false because that's what MonetDB is for
 	 */
 	@Override
 	public boolean usesLocalFiles() {
 		return false;
 	}
 	/**
-	 * Does the database use a local file for each table?  Well, not really,
+	 * Does the database use a local file for each table?
-	 * since it doesn't use local files.
 	 *
 	 * @return false for it doesn't
 	 */
 	@Override
 	public boolean usesLocalFilePerTable() {
 	public boolean supportsOuterJoins(){
 		return true;
 	}
 	/**
-	 * Are full nexted outer joins supported?
+	 * Are full nested outer joins supported?
 	 *
 	 * @return true if so
 	 */
 	@Override
 	public boolean supportsFullOuterJoins() {
 		return true;
 	}
 	/**
 	 * How many hex characters can you have in an inline binary literal
-	 * I honestly wouldn't know...
 	 *
 	 * @return the max literal length
 	 */
 	@Override
 	public int getMaxBinaryLiteralLength() {
-		return 0; // no limit
+		return 2*1024*1024*1024 - 2;	// MonetDB supports null terminated strings of max 2GB, see function: int UTF8_strlen()
 	}
 	/**
 	 * What is the maximum length for a character literal
-	 * Is there a max?
 	 *
 	 * @return the max literal length
 	 */
 	@Override
 	public int getMaxCharLiteralLength() {
-		return 0; // no limit
+		return 2*1024*1024*1024 - 2;	// MonetDB supports null terminated strings of max 2GB, see function: int UTF8_strlen()
 	}
 	/**
 	 * Whats the limit on column name length.
 	 * I take some safety here, but it's just a varchar in MonetDB
 	 *
 	 * @return the maximum column name length
 	 */
 	@Override
 	public int getMaxColumnNameLength() {
-		return 1024;
+		return 1024;	// In MonetDB the max length of column sys._columns.name is defined as 1024
 	}
 	/**
 	 * What is the maximum number of columns in a "GROUP BY" clause?
 	 *
 	 * @return the max number of columns
 	 */
 	@Override
 	public int getMaxColumnsInGroupBy() {
-		return 0; // no limit
+		return 0;	// no specific limit known
 	}
 	/**
 	 * What's the maximum number of columns allowed in an index?
 	 *
 	 * @return max number of columns
 	 */
 	@Override
 	public int getMaxColumnsInIndex() {
-		return 0;	// unlimited I guess
+		return 0;	// no specific limit known
 	}
 	/**
 	 * What's the maximum number of columns in an "ORDER BY clause?
 	 *
 	 * @return the max columns
 	 */
 	@Override
 	public int getMaxColumnsInOrderBy() {
-		return 0; // unlimited I guess
+		return 0;	// no specific limit known
 	}
 	/**
 	 * What is the maximum number of columns in a "SELECT" list?
 	 *
 	 * @return the max columns
 	 */
 	@Override
 	public int getMaxColumnsInSelect() {
-		return 0; // unlimited I guess
+		return 0;	// no specific limit known
 	}
 	/**
 	 * What is the maximum number of columns in a table?
-	 * wasn't MonetDB designed for datamining? (= much columns)
+	 *
+	 * The theoretical max value of int column sys._columns.id is 2^31 -1
+	 * but this is for all columns of all tables in all schemas (including all data dictionary columns).
+	 * For one table we should reduce it to a more practical soft limit of say 100 thousand
 	 *
 	 * @return the max columns
 	 */
 	@Override
 	public int getMaxColumnsInTable() {
-		return 0;
+		return 100*1000;	// soft limit it to 100 thousand
 	}
 	/**
 	 * How many active connections can we have at a time to this
 	 * database?  Well, since it depends on Mserver, which just listens
 	 *
 	 * @return max cursor name length in bytes
 	 */
 	@Override
 	public int getMaxCursorNameLength() {
-		return 1024;
+		return 0;	// no specific limit known
 	}
 	/**
 	 * Retrieves the maximum number of bytes for an index, including all
 	 * of the parts of the index.
 	 *         of all the constituent parts of the index; a result of zero
 	 *         means that there is no limit or the limit is not known
 	 */
 	@Override
 	public int getMaxIndexLength() {
-		return 0; // I assume it is large, but I don't know
+		return 0;	// no specific limit known
 	}
 	/**
 	 * Retrieves the maximum number of characters that this database
 	 * allows in a schema name.
 	 * @return the number of characters or 0 if there is no limit, or the
 	 *         limit is unknown.
 	 */
 	@Override
 	public int getMaxSchemaNameLength() {
-		return 1024;
+		return 1024;	// In MonetDB the max length of column sys.schemas.name is defined as 1024
 	}
 	/**
 	 * What is the maximum length of a procedure name
 	 *
 	 * @return the max name length in bytes
 	 */
 	@Override
 	public int getMaxProcedureNameLength() {
-		return 1024;
+		return 256;	// In MonetDB the max length of column sys.functions.name is defined as 256
 	}
 	/**
 	 * What is the maximum length of a catalog
 	 *
 	public int getMaxRowSize() {
 		return 0;	// very long I hope...
 	}
 	/**
-	 * Did getMaxRowSize() include LONGVARCHAR and LONGVARBINARY
+	 * Did getMaxRowSize() include the SQL data types LONGVARCHAR and LONGVARBINARY
 	 * blobs?
 	 * Yes I thought so...
 	 *
 	 * @return true if so
 	 */
 		return true;
 	}
 	/**
 	 * What is the maximum length of a SQL statement?
-	 * Till a programmer makes a mistake and causes a segmentation fault
-	 * on a string overflow...
 	 *
 	 * @return max length in bytes
 	 */
 	@Override
 	public int getMaxStatementLength() {
-		return 0;		// actually whatever fits in size_t
+		return 2*1024*1024*1024 - 2;	// MonetDB supports null terminated strings of max 2GB, see function: int UTF8_strlen()
 	}
 	/**
 	 * How many active statements can we have open at one time to
 	 * this database?  Basically, since each Statement downloads
 	 *
 	 * @return the maximum
 	 */
 	@Override
 	public int getMaxStatements() {
-		return 0;
+		return 0;	// no specific limit known
 	}
 	/**
 	 * What is the maximum length of a table name
 	 *
 	 * @return max name length in bytes
 	 */
 	@Override
 	public int getMaxTableNameLength() {
-		return 1024;
+		return 1024;	// In MonetDB the max length of column sys._tables.name is defined as 1024
 	}
 	/**
 	 * What is the maximum number of tables that can be specified
 	 * in a SELECT?
 	 *
 	 * @return the maximum
 	 */
 	@Override
 	public int getMaxTablesInSelect() {
-		return 0; // no limit
+		return 0;	// no specific limit known
 	}
 	/**
 	 * What is the maximum length of a user name
 	 *
 	 * @return the max name length in bytes
 	 */
 	@Override
 	public int getMaxUserNameLength() {
-		return 512;
+		return 1024;	// In MonetDB the max length of column sys.db_user_info.name is defined as 1024
 	}
 	/**
 	 * What is the database's default transaction isolation level?
 	 * We only see commited data, nonrepeatable reads and phantom
 	 *	<LI><B>SOURCE_DATA_TYPE</B> short => source type of a distinct type or user-generated Ref type, SQL type from java.sql.Types (null if DATA_TYPE isn't DISTINCT or user-generated REF)
 	 *	<LI><B>IS_AUTOINCREMENT</B> String => Indicates whether this column is auto incremented
 	 *		<UL>
 	 *		<LI> YES --- if the column is auto incremented
 	 *		<LI> NO --- if the column is not auto incremented
 	 *		<LI> empty string --- if it cannot be determined whether the column is auto incremented
 	 *		</UL>
 	 *	<LI><B>IS_GENERATEDCOLUMN</B> String => Indicates whether this is a generated column
 	 *		<UL>
 	 *		<LI> YES --- if this a generated column
 	 *		<LI> NO --- if this not a generated column
 	 *		scope of a reference attribute (<code>null</code> if DATA_TYPE isn't REF)
 	 *	<LI><B>SCOPE_SCHEMA</B> String => schema of table that is the
 	 *		scope of a reference attribute (<code>null</code> if DATA_TYPE isn't REF)
 	 *	<LI><B>SCOPE_TABLE</B> String => table name that is the scope of a
 	 *		reference attribute (<code>null</code> if the DATA_TYPE isn't REF)
-	 * 	<LI><B>SOURCE_DATA_TYPE</B> short => source type of a distinct type or user-generated
+	 *	<LI><B>SOURCE_DATA_TYPE</B> short => source type of a distinct type or user-generated
 	 *		Ref type,SQL type from java.sql.Types (<code>null</code> if DATA_TYPE
 	 *		isn't DISTINCT or user-generated REF)
 	 *	</OL>
 	 * @param catalog a catalog name; must match the catalog name as it
 	 *		  is stored in the database; "" retrieves those without a catalog;
 				major = Integer.parseInt((start >= 0) ? env_monet_version.substring(0, start) : env_monet_version);
 			} catch (NumberFormatException e) {
 				// ignore
 			}
 		}
 		return major;
 	}
 	/**
 	 * Retrieves the minor version number of the underlying database.
 	 *
 				}
 			} catch (NumberFormatException e) {
 				// ignore
 			}
 		}
 		return minor;
 	}
 	/**
 	 * Retrieves the major JDBC version number for this driver.
 	 *
 	public ResultSet getClientInfoProperties() throws SQLException {
 		// for a list of connection properties see also MonetConnection.java constructor MonetConnection(Properties props)
 		String query =
 		"SELECT 'host' AS \"NAME\", CAST(1024 as int) AS \"MAX_LEN\", 'localhost' AS \"DEFAULT_VALUE\", 'DSN or IP-address of machine running MonetDB' AS \"DESCRIPTION\" UNION ALL " +
 		"SELECT 'port', 5, '50000', 'communication port number of MonetDB server process' UNION ALL " +
-		"SELECT 'user', 128, '', 'user name to login to MonetDB server' UNION ALL " +
+		"SELECT 'user', 1024, '', 'user name to login to MonetDB server' UNION ALL " +
 		"SELECT 'password', 128, '', 'password for user name to login to MonetDB server' UNION ALL " +
 		"SELECT 'language', 16, 'sql', 'language (sql or mal) used to parse commands in MonetDB server' UNION ALL " +
 		"SELECT 'debug', 5, 'false', 'boolean flag true or false' UNION ALL " +
 		"SELECT 'hash', 128, '', 'hash string' UNION ALL " +
 		"SELECT 'treat_blob_as_binary', 5, 'false', 'boolean flag true or false' UNION ALL " +
 	 *         functionNullable - allows NULL values
 	 *         functionNullableUnknown - nullability unknown
 	 * 13.  REMARKS String => comment describing column/parameter
 	 * 14.  CHAR_OCTET_LENGTH int => the maximum length of binary and character based parameters or columns. For any other datatype the returned value is a NULL
 	 * 15.  ORDINAL_POSITION int => the ordinal position, starting from 1, for the input and output parameters.
-	 * 	   A value of 0 is returned if this row describes the function's return value. For result set columns, it is the ordinal position of the column in the result set starting from 1.
+	 *	   A value of 0 is returned if this row describes the function's return value. For result set columns, it is the ordinal position of the column in the result set starting from 1.
 	 * 16.  IS_NULLABLE String => ISO rules are used to determine the nullability for a parameter or column.
 	 *         YES --- if the parameter or column can include NULLs
 	 *         NO --- if the parameter or column cannot include NULLs
 	 *         empty string --- if the nullability for the parameter or column is unknown
 	 * 17.  SPECIFIC_NAME String => the name which uniquely identifies this function within its schema.
-	 * 	  This is a user specified, or DBMS generated, name that may be different then the FUNCTION_NAME for example with overload functions
+	 *	  This is a user specified, or DBMS generated, name that may be different then the FUNCTION_NAME for example with overload functions
 	 *
 	 * @param catalog a catalog name; must match the catalog name as
 	 *        it is stored in the database; "" retrieves those without a
 	 *        catalog; null means that the catalog name should not be
 	 *        used to narrow the search

Mercurial > hg > monetdb-java

comparison src/main/java/nl/cwi/monetdb/jdbc/MonetDatabaseMetaData.java @ 15:6e48d0fae766