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java.lang.Object org.hsqldb.jdbc.jdbcResultSetMetaData
An object that can be used to get information about the types
and properties of the columns in a ResultSet
object.
The following code fragment creates the ResultSet
object rs, creates the ResultSetMetaData
object rsmd,
and uses rsmd to find out how many columns rs has and whether the
first column in rs can be used in a WHERE
clause.
ResultSet rs = stmt.executeQuery("SELECT a, b, c FROM TABLE2"); ResultSetMetaData rsmd = rs.getMetaData(); int numberOfColumns = rsmd.getColumnCount(); boolean b = rsmd.isSearchable(1);
HSQLDB supports a subset of the ResultSetMetaData
interface.
The JDBC specification for ResultSetMetaData
is in part very
vague. This causes potential incompatibility between interpretations of the
specification as realized in different JDBC driver implementations. As such,
deciding to what degree reporting ResultSetMetaData is accurate has been
considered very carefully. Hopefully, the design decisions made in light of
these considerations have yeilded precisely the subset of full
ResultSetMetaData support that is most commonly needed and that is most
important, while also providing, under the most common use-cases, the
fastest access with the least overhead and the best comprimise between
speed, accuracy, jar-foootprint and retention of JDBC resources.
(fredt@users)
(boucherb@users)
jdbcStatement.executeQuery(java.lang.String)
,
jdbcStatement.getResultSet()
,
ResultSetMetaData
Field Summary |
Fields inherited from interface java.sql.ResultSetMetaData |
columnNoNulls, columnNullable, columnNullableUnknown |
Method Summary | |
java.lang.String |
getCatalogName(int column)
Gets the designated column's table's catalog name. |
java.lang.String |
getColumnClassName(int column)
Returns the fully-qualified name of the Java class whose instances are manufactured if the method ResultSet.getObject
is called to retrieve a value from the column. |
int |
getColumnCount()
Returns the number of columns in this ResultSet
object. |
int |
getColumnDisplaySize(int column)
Indicates the designated column's normal maximum width in characters. |
java.lang.String |
getColumnLabel(int column)
Gets the designated column's suggested title for use in printouts and displays. |
java.lang.String |
getColumnName(int column)
Get the designated column's name. |
int |
getColumnType(int column)
Retrieves the designated column's SQL type. |
java.lang.String |
getColumnTypeName(int column)
Retrieves the designated column's database-specific type name. |
int |
getPrecision(int column)
Get the designated column's number of decimal digits. |
int |
getScale(int column)
Gets the designated column's number of digits to right of the decimal point. |
java.lang.String |
getSchemaName(int column)
Get the designated column's table's schema. |
java.lang.String |
getTableName(int column)
Gets the designated column's table name. |
boolean |
isAutoIncrement(int column)
Indicates whether the designated column is automatically numbered, thus read-only. |
boolean |
isCaseSensitive(int column)
Indicates whether a column's case matters. |
boolean |
isCurrency(int column)
Indicates whether the designated column is a cash value. |
boolean |
isDefinitelyWritable(int column)
Indicates whether a write on the designated column will definitely succeed. |
int |
isNullable(int column)
Indicates the nullability of values in the designated column. |
boolean |
isReadOnly(int column)
Indicates whether the designated column is definitely not writable. |
boolean |
isSearchable(int column)
Indicates whether the designated column can be used in a where clause. |
boolean |
isSigned(int column)
Indicates whether values in the designated column are signed numbers. |
boolean |
isWritable(int column)
Indicates whether it is possible for a write on the designated column to succeed. |
java.lang.String |
toString()
|
Methods inherited from class java.lang.Object |
equals, getClass, hashCode, notify, notifyAll, wait, wait, wait |
Method Detail |
public int getColumnCount() throws java.sql.SQLException
ResultSet
object.
getColumnCount
in interface java.sql.ResultSetMetaData
java.sql.SQLException
- if a database access error occurspublic boolean isAutoIncrement(int column) throws java.sql.SQLException
HSQLDB 1.7.1 did not report this value accurately, either always throwing or always returning false, depending upon client property values.
Starting with HSQLDB 1.7.2, this feature is better supported.
In fact, the generic documentation above seems to contradict the general definition of what, at minimum, an auto-increment column is:
Simply, an auto-increment column is one that guarantees it has a unique value after a successful insert or update operation, even if no value is supplied or NULL is explicitly specified by the application or a default value expression.
Further, without SQL Feature T176, Sequence generator support, the attributes of the internal source consulted for unique values are not defined. That is, unlike for a standard SQL SEQUENCE object or a system with full SQL 9x or 200n support for SQL Feature T174, Identity columns, an application must not assume and cannot determine in a standard way that auto-increment values start at any particular point, increment by any particular value or have any of the other attributes generally associated with SQL SEQUENCE generators. Further still, without full support for both feature T174 and T176, if a unique value is supplied by an application or provided by a declared or implicit default value expression, then whether that value is used or substituted with one from the automatic unique value source is implementation-defined and cannot be known in a standard way. Finally, without full support for features T174 and T176, it is also implementation-defined and cannot be know in a standard way whether an exception is thrown or a unique value is automatically substituted when an application or default value expression supplies a non-NULL, non-unique value.
Up to and including HSQLDB 1.7.2, values supplied by an application or default value expression are used if they are indeed non-NULL unique values, while an exception is thrown if either possible value source for the site attempts to supply a non-NULL, non-unique value. This is very likely to remain the behaviour of HSQLDB for its foreseable lifetime and at the very least for the duration of the 1.7.x release series.
Under such special circumstances, the driver rethrows the exception that occured during the initialization, or a SQLException wrapping it.
Those wishing to determine the auto-increment status of a table column in isolation from ResultSetMetaData can do so by inspecting the corresponding value of the SYSTEM_COLUMNS.IS_IDENTITY BOOLEAN column which is also currently included (in a fashion proprietary to HSQLDB) as the last column of the jdbcDatabaseMetaData.getColumns() result.
isAutoIncrement
in interface java.sql.ResultSetMetaData
column
- the first column is 1, the second is 2, ...
true
if so; false
otherwise
java.sql.SQLException
- if a database access error occurspublic boolean isCaseSensitive(int column) throws java.sql.SQLException
HSQLDB 1.7.1 did not report this value accurately.
Starting with 1.7.2, this feature is better supported.
This method returns true for any column whose data type is a character type, with the exception of VARCHAR_IGNORECASE for which it returns false. It also returns false for any column whose data type is a not a character data type.
isCaseSensitive
in interface java.sql.ResultSetMetaData
column
- the first column is 1, the second is 2, ...
true
if so; false
otherwise
java.sql.SQLException
- if a database access error occurspublic boolean isSearchable(int column) throws java.sql.SQLException
HSQLDB 1.7.1 did not report this value accurately.
Starting with 1.7.2, this feature is better supported.
If the data type of the column is definitely known to be searchable in any way under HSQLDB, then true is returned, else false. That is, if the type is reported in DatabaseMetaData.getTypeInfo() as having DatabaseMetaData.typePredNone or is not reported, then false is returned, else true.
isSearchable
in interface java.sql.ResultSetMetaData
column
- the first column is 1, the second is 2, ...
true
if so; false
otherwise
java.sql.SQLException
- if a database access error occurspublic boolean isCurrency(int column) throws java.sql.SQLException
Up to and including HSQLDB 1.7.2, this method always returns false.
This is because true fixed (precision,scale) data types are not yet supported. That is, DECIMAL and NUMERIC types are implemented as a thin wrap of java.math.BigDecimal, which cannot, without additional, as yet unimplemented constraint enforcement code, be said to be a fixed (precision,scale) types.
isCurrency
in interface java.sql.ResultSetMetaData
column
- the first column is 1, the second is 2, ...
true
if so; false
otherwise
java.sql.SQLException
- if a database access error occurspublic int isNullable(int column) throws java.sql.SQLException
Up to 1.7.1, HSQLDB did not report this value accurately.
Starting with 1.7.2, this feature is better supported.
columnNullableUnknown is always returned for result set columns that do not directly represent table column values (i.e. are calculated), while the corresponding value in SYSTEM_COLUMNS.NULLABLE is returned for result set columns that do directly represent table column values.
Those wishing to determine the nullable status of a table column in isolation from ResultSetMetaData and in a DBMS-independent fashion can do so by calling DatabaseMetaData.getColumns() with the appropriate filter values and inspecting the result at the position described in the API documentation.
isNullable
in interface java.sql.ResultSetMetaData
column
- the first column is 1, the second is 2, ...
columnNoNulls
,
columnNullable
or columnNullableUnknown
java.sql.SQLException
- if a database access error occurspublic boolean isSigned(int column) throws java.sql.SQLException
HSQLDB 1.7.1 introduced support for this feature and 1.7.2 reports identical values (although using a slightly different implementation).
isSigned
in interface java.sql.ResultSetMetaData
column
- the first column is 1, the second is 2, ...
true
if so; false
otherwise
java.sql.SQLException
- if a database access error occurspublic int getColumnDisplaySize(int column) throws java.sql.SQLException
Up to and including HSQLDB 1.7.1, this method always returned 0, which was intended to convey unknown display size. Unfortunately, this value is not universally handled by all clients and in the worst case can cause some applications to crash.
Starting with 1.7.2, this feature is better supported.
The current calculation follows these rules:
The maximum length/precision, repectively.
The max precision, plus the length of the negation character (1), plus (if applicable) the maximum number of characters that may occupy the exponent character sequence. Note that some legacy tools do not correctly handle BIGINT values of greater than 18 digits.
The length of the character sequence "false" (5), the longer of the two boolean value String representations.
The maximum length/precision, respectively, as reported by DatabaseMetaData.getTypeInfo(), when applicable. If the maximum display size is unknown, unknowable or inapplicable, then zero is returned.
getColumnDisplaySize
in interface java.sql.ResultSetMetaData
column
- the first column is 1, the second is 2, ...
java.sql.SQLException
- if a database access error occurspublic java.lang.String getColumnLabel(int column) throws java.sql.SQLException
In HSQLDB a ResultSet
column label is determined in the
following order of precedence:
String
.
getColumnLabel
in interface java.sql.ResultSetMetaData
column
- the first column is 1, the second is 2, ...
java.sql.SQLException
- if a database access error occurspublic java.lang.String getColumnName(int column) throws java.sql.SQLException
In HSQLDB a ResultSet column name is determined in the following order of prcedence:
String
.
If the jdbc.get_column_name
property of the database
has been set to false, this method returns the same value as
getColumnLabel(int)
.
getColumnName
in interface java.sql.ResultSetMetaData
column
- the first column is 1, the second is 2, ...
java.sql.SQLException
- if a database access error occurspublic java.lang.String getSchemaName(int column) throws java.sql.SQLException
Up to 1.7.1, HSQLDB did not support the notion of schemas at all, including schema names in result set metadata; this method always returned "".
Staring with 1.7.2, schema name reporting is supported only as an optional, experimental feature that is disabled by default. Enabling this feature requires setting the database property "hsqldb.schemas=true".
Specifically, when this feature is enabled under 1.7.2, only very limited support is provided by the engine for executing SQL containing schema-qualified database object identifiers. That is, when this feature is enabled under 1.7.2, it is not yet possible in most cases to use what would otherwise be the correct, canonical SQL calculated from ResultSetMetaData.
Regardless, reporting is done only in system table content and is not yet carried over to ResultSetMetaData.
For greater detail, see discussion at:
jdbcDatabaseMetaData
.
getSchemaName
in interface java.sql.ResultSetMetaData
column
- the first column is 1, the second is 2, ...
java.sql.SQLException
- if a database access error occurspublic int getPrecision(int column) throws java.sql.SQLException
Starting with 1.8.0, HSQLDB reports the the declared length or precision specifiers for table columns (if they are defined, which up to 1.7.2 is not a requirement in DDL), as these values may or may not be enforced, depending on the value of the database property:
sql.enforce_strict_sizeBecause the property may change from one instantiation of a Database to the next and because, when set true, is not applied to existing values in table columns (only to new values introduced by following inserts and updates), the length and/or precision specifiers for table columns still do not neccessarily accurately reflect true constraints upon the contents of the columns. This situation may or may not change in a future release.
getPrecision
in interface java.sql.ResultSetMetaData
column
- the first column is 1, the second is 2, ...
java.sql.SQLException
- if a database access error occurspublic int getScale(int column) throws java.sql.SQLException
Starting with 1.8.0, HSQLDB reports the declared scale for table columns depending on the value of the database property:
sql.enforce_strict_size
getScale
in interface java.sql.ResultSetMetaData
column
- the first column is 1, the second is 2, ...
java.sql.SQLException
- if a database access error occurspublic java.lang.String getTableName(int column) throws java.sql.SQLException
getTableName
in interface java.sql.ResultSetMetaData
column
- the first column is 1, the second is 2, ...
java.sql.SQLException
- if a database access error occurspublic java.lang.String getCatalogName(int column) throws java.sql.SQLException
Up to and including 1.7.1, HSQLDB did not support the notion of catalog and this method always returned "".
Starting with 1.7.2, HSQLDB supports catalog reporting only as an optional, experimental feature that is disabled by default. Enabling this feature requires setting the database property "hsqldb.catalogs=true". When enabled, the catalog name for table columns is reported as the name by which the hosting Database knows itself.
HSQLDB does not yet support any use of catalog qualification in DLL or DML. This fact is accurately indicated in the corresponding DatabaseMetaData.supportsXXX() method return values.
Regardless, reporting is done only in system table content and is not yet carried over to ResultSetMetaData.
For greater detail, see discussion at:
jdbcDatabaseMetaData
.
getCatalogName
in interface java.sql.ResultSetMetaData
column
- the first column is 1, the second is 2, ...
java.sql.SQLException
- if a database access error occurspublic int getColumnType(int column) throws java.sql.SQLException
This reports the SQL type of the column. HSQLDB can return Objects in
any Java integral type wider than Integer
for an SQL
integral type.
getColumnType
in interface java.sql.ResultSetMetaData
column
- the first column is 1, the second is 2, ...
java.sql.SQLException
- if a database access error occursTypes
public java.lang.String getColumnTypeName(int column) throws java.sql.SQLException
getColumnTypeName
in interface java.sql.ResultSetMetaData
column
- the first column is 1, the second is 2, ...
java.sql.SQLException
- if a database access error occurspublic boolean isReadOnly(int column) throws java.sql.SQLException
Up to and including 1.7.1, HSQLDB did not report this value accurately.
Starting with HSQLDB 1.7.2, this feature is better supported.
For result set columns that do not directly represent table column values (i.e. are calculated), true is reported. Otherwise, the read only status of the table and the database are used in the calculation, but not the read-only status of the session.
isReadOnly
in interface java.sql.ResultSetMetaData
column
- the first column is 1, the second is 2, ...
true
if so; false
otherwise
java.sql.SQLException
- if a database access error occurspublic boolean isWritable(int column) throws java.sql.SQLException
Up to and including 1.7.1, HSQLDB did not report this value accurately.
Starting with HSQLDB 1.7.2, this feature is better supported.
In essense, the negation of isReadOnly() is reported.
isWritable
in interface java.sql.ResultSetMetaData
column
- the first column is 1, the second is 2, ...
true
if so; false
otherwise
java.sql.SQLException
- if a database access error occurspublic boolean isDefinitelyWritable(int column) throws java.sql.SQLException
HSQLDB 1.7.1 did not report this value accurately.
Starting with HSQLDB 1.7.2, this method always returns false. The reason for this is that it is generally either very complex or simply impossible to calculate deterministically true for table columns under all concievable conditions. The value is of dubious usefulness, except perhaps if there were support for updateable result sets using "SELECT ... FOR UPDATE" style locking. However, this is not anticipated to occur any time in the 1.7.x release series.
isDefinitelyWritable
in interface java.sql.ResultSetMetaData
column
- the first column is 1, the second is 2, ...
true
if so; false
otherwise
java.sql.SQLException
- if a database access error occurspublic java.lang.String getColumnClassName(int column) throws java.sql.SQLException
ResultSet.getObject
is called to retrieve a value from the column.
ResultSet.getObject
may return a subclass of the class
returned by this method.
HSQLDB 1.7.1 did not support this feature; calling this method
always caused an SQLException
to be thrown,
stating that the function was not supported.
getColumnClassName
in interface java.sql.ResultSetMetaData
column
- the first column is 1, the second is 2, ...
ResultSet.getObject
to retrieve the value in the
specified column. This is the class name used for custom mapping.
java.sql.SQLException
- if a database access error occurspublic java.lang.String toString()
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