org.hsqldb.jdbc

Class JDBCResultSetMetaData

java.lang.Object

org.hsqldb.jdbc.JDBCResultSetMetaData

All Implemented Interfaces:

ResultSetMetaData, Wrapper

public class JDBCResultSetMetaData
extends Object
implements ResultSetMetaData

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-Specific Information:

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-footprint and retention of JDBC resources.

(fredt@users)
(campbell-burnet@users)

Author:

Campbell Burnet (campbell-burnet@users dot sourceforge.net), Fred Toussi (fredt@users dot sourceforge.net)

See Also:

JDBCStatement.executeQuery(java.lang.String), JDBCStatement.getResultSet(), ResultSetMetaData

Field Summary

Fields inherited from interface java.sql.ResultSetMetaData

columnNoNulls, columnNullable, columnNullableUnknown

Method Summary

Modifier and Type	Method and Description
String	getCatalogName(int column) Gets the designated column's table's catalog name.
String	getColumnClassName(int 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.
String	getColumnLabel(int column) Gets the designated column's suggested title for use in printouts and displays.
String	getColumnName(int column) Get the designated column's name.
int	getColumnType(int column) Retrieves the designated column's SQL type.
String	getColumnTypeName(int column) Retrieves the designated column's database-specific type name.
int	getPrecision(int column) (JDBC4 clarification:) Get the designated column's specified column size.
int	getScale(int column) Gets the designated column's number of digits to right of the decimal point.
String	getSchemaName(int column) Get the designated column's table's schema.
String	getTableName(int column) Gets the designated column's table name.
boolean	isAutoIncrement(int column) Indicates whether the designated column is automatically numbered.
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	isWrapperFor(Class<?> iface) Returns true if this either implements the interface argument or is directly or indirectly a wrapper for an object that does.
boolean	isWritable(int column) Indicates whether it is possible for a write on the designated column to succeed.
String	toString() Returns a string representation of the object.
<T> T	unwrap(Class<T> iface) Returns an object that implements the given interface to allow access to non-standard methods, or standard methods not exposed by the proxy.

Methods inherited from class java.lang.Object

equals, getClass, hashCode, notify, notifyAll, wait, wait, wait

Method Detail

getColumnCount

public int getColumnCount()
                   throws SQLException

Returns the number of columns in this ResultSet object.

Specified by:

getColumnCount in interface ResultSetMetaData

Returns:

the number of columns

Throws:

SQLException - if a database access error occurs

isAutoIncrement

public boolean isAutoIncrement(int column)
                        throws SQLException

Indicates whether the designated column is automatically numbered.

(JDBC4 deleted:)[, thus read-only.]

HSQLDB-Specific Information:

HSQLDB 2.0 fully supports SQL Satandard features T174 and T176 that define identity column support.

However, it must be stated here that contrary to the generic documentation previous to the JDBC4 specification, HSQLDB automatically numbered columns (IDENTITY columns, in HSQLDB parlance) are not read-only.

In fact, the generic documentation previous to the JDBC4 specification 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 autogenerated value after a successful insert or update operation, even if no value is supplied, or DEFAULT is specified.

Specified by:

isAutoIncrement in interface ResultSetMetaData

Parameters:

column - the first column is 1, the second is 2, ...

Returns:

true if so; false otherwise

Throws:

SQLException - if a database access error occurs

isCaseSensitive

public boolean isCaseSensitive(int column)
                        throws SQLException

Indicates whether a column's case matters.

HSQLDB-Specific Information:

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.

Specified by:

isCaseSensitive in interface ResultSetMetaData

Parameters:

column - the first column is 1, the second is 2, ...

Returns:

true if so; false otherwise

Throws:

SQLException - if a database access error occurs

isSearchable

public boolean isSearchable(int column)
                     throws SQLException

Indicates whether the designated column can be used in a where clause.

HSQLDB-Specific Information:

HSQLDB 2.0 handles this differently from previous versions.

If the column in question is a database table or view column, and the type of the column allows searching, then returns true, otherwise false.

Specified by:

isSearchable in interface ResultSetMetaData

Parameters:

column - the first column is 1, the second is 2, ...

Returns:

true if so; false otherwise

Throws:

SQLException - if a database access error occurs

isCurrency

public boolean isCurrency(int column)
                   throws SQLException

Indicates whether the designated column is a cash value.

HSQLDB-Specific Information:

HSQLDB 2.0 fully supports this feature and returns true for NUMERIC and DECIMAL columns.

Specified by:

isCurrency in interface ResultSetMetaData

Parameters:

column - the first column is 1, the second is 2, ...

Returns:

true if so; false otherwise

Throws:

SQLException - if a database access error occurs

isNullable

public int isNullable(int column)
               throws SQLException

Indicates the nullability of values in the designated column.

HSQLDB-Specific Information:

HSQLDB 2.2 fully supports this feature.

columnNoNulls is always returned for result set columns that represent constants, sequences or table columns known to be not null. columnNullable is returned for NULL constants, or nullable table columns. columnNullableUnknown is returned for all other columns such as aggregates and computed values.

To determine the nullable status of a table column in isolation from ResultSetMetaData and in a DBMS-independent fashion, the DatabaseMetaData.getColumns() method can be invoked with the appropriate filter values and the result should be inspected at the position described in the DatabaseMetaData.getColumns() API documentation.

Specified by:

isNullable in interface ResultSetMetaData

Parameters:

column - the first column is 1, the second is 2, ...

Returns:

the nullability status of the given column; one of columnNoNulls, columnNullable or columnNullableUnknown

Throws:

SQLException - if a database access error occurs

isSigned

public boolean isSigned(int column)
                 throws SQLException

Indicates whether values in the designated column are signed numbers.

HSQLDB-Specific Information:

HSQLDB 2.0 fully supports this feature.

Specified by:

isSigned in interface ResultSetMetaData

Parameters:

column - the first column is 1, the second is 2, ...

Returns:

true if so; false otherwise

Throws:

SQLException - if a database access error occurs

getColumnDisplaySize

public int getColumnDisplaySize(int column)
                         throws SQLException

Indicates the designated column's normal maximum width in characters.

HSQLDB-Specific Information:

HSQLDB 2.0 fully supports this feature.

The current calculation follows these rules:

1. Long character types and datetime types:

   The maximum length/precision, repectively.

2. CHAR and VARCHAR types:
   • If the result set column is a direct pass through of a table column value and column size was declared, then the declared value is returned.
   • Otherwise, the computed length according to SQL Standard is returned. For very large values, the value of the system property hsqldb.max_xxxchar_display_size or the magic value 32766 (0x7FFE) (tested usable/accepted by most tools and compatible with assumptions made by java.io read/write UTF) when the system property is not defined or is not accessible, due to security constraints.

   It must be noted that the latter value in no way affects the ability of the HSQLDB JDBC driver to retrieve longer values and serves only as the current best effort at providing a value that maximizes usability across a wide range of tools, given that the HSQLDB database engine allows very large lengths to be declared.
3. Number types:

   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.

4. BOOLEAN type:

   The length of the character sequence "false" (5), the longer of the two boolean value String representations.

5. Remaining types:

   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.

Specified by:

getColumnDisplaySize in interface ResultSetMetaData

Parameters:

column - the first column is 1, the second is 2, ...

Returns:

the normal maximum number of characters allowed as the width of the designated column

Throws:

SQLException - if a database access error occurs

getColumnLabel

public String getColumnLabel(int column)
                      throws SQLException

Gets the designated column's suggested title for use in printouts and displays. (JDBC4 clarification:) The suggested title is usually specified by the SQL AS clause. If a SQL AS is not specified, the value returned from getColumnLabel will be the same as the value returned by the getColumnName method.

HSQLDB-Specific Information:

In HSQLDB, a ResultSet column label is determined using the following order of precedence:

1. The label (alias) specified in the generating query.
2. The name of the underlying column, if no label is specified.
   
3. C1, C2, etc. for computed columns that have no label.

Specified by:

getColumnLabel in interface ResultSetMetaData

Parameters:

column - the first column is 1, the second is 2, ...

Returns:

the suggested column title

Throws:

SQLException - if a database access error occurs

getColumnName

public String getColumnName(int column)
                     throws SQLException

Get the designated column's name.

HSQLDB-Specific Information:

In HSQLDB, a ResultSet column name is determined using the following order of precedence:

1. The name of the underlying column, if the ResultSet column represents a column in a table.
2. The label or alias specified in the generating query.
3. C1, C2, etc. for computed columns that have no label.

If the jdbc.get_column_name property of the JDBC Connection has been set to false, this method returns the same value as getColumnLabel(int).

Specified by:

getColumnName in interface ResultSetMetaData

Parameters:

column - the first column is 1, the second is 2, ...

Returns:

column name

Throws:

SQLException - if a database access error occurs

getSchemaName

public String getSchemaName(int column)
                     throws SQLException

Get the designated column's table's schema.

HSQLDB-Specific Information:

Since 1.8.0.x, HSQLDB implements standard SQL SCHEMA support; this method returns the actual schema of the column's table. Columns generated in queries have no schema name.

Specified by:

getSchemaName in interface ResultSetMetaData

Parameters:

column - the first column is 1, the second is 2, ...

Returns:

schema name or "" if not applicable

Throws:

SQLException - if a database access error occurs

getPrecision

public int getPrecision(int column)
                 throws SQLException

(JDBC4 clarification:) Get the designated column's specified column size. For numeric data, this is the maximum precision. For character data, this is the [maximum] length in characters. For datetime datatypes, this is the [maximum] length in characters of the String representation (assuming the maximum allowed precision of the fractional seconds component). For binary data, this is the [maximum] length in bytes. For the ROWID datatype, this is the length in bytes[, as returned by the implementation-specific java.sql.RowId.getBytes() method]. 0 is returned for data types where the column size is not applicable.

HSQLDB-Specific Information:

HSQLDB 2.0 reports the correct length or precision for all columns. For DOUBLE, the binary precision of 64 is returned, while for other numeric types the decimal precision is returned.

Specified by:

getPrecision in interface ResultSetMetaData

Parameters:

column - the first column is 1, the second is 2, ...

Returns:

precision

Throws:

SQLException - if a database access error occurs

getScale

public int getScale(int column)
             throws SQLException

Gets the designated column's number of digits to right of the decimal point. 0 is returned for data types where the scale is not applicable.

HSQLDB-Specific Information:

HSQLDB 2.0 reports the correct scale for all columns.

For datetime and interval types such as Timestamp or Time, the fractional second precision is reported.

The reported scale for INTEGER, BIGINT and DOUBLE is 0

Specified by:

getScale in interface ResultSetMetaData

Parameters:

column - the first column is 1, the second is 2, ...

Returns:

scale

Throws:

SQLException - if a database access error occurs

getTableName

public String getTableName(int column)
                    throws SQLException

Gets the designated column's table name.

Specified by:

getTableName in interface ResultSetMetaData

Parameters:

column - the first column is 1, the second is 2, ...

Returns:

table name or "" if not applicable

Throws:

SQLException - if a database access error occurs

getCatalogName

public String getCatalogName(int column)
                      throws SQLException

Gets the designated column's table's catalog name.

HSQLDB-Specific Information:

From 2.0, HSQLDB returns the name of the catalog. The default name is PUBLIC. This value can be changed for the database using an SQL command.

HSQLDB supports use of catalog qualification in DLL or DML when it is allowed by the Standard.

However, not all clients respect the SQL Standard and may use a catalog qualifier in a context where it is not supported by the Standard.

For greater detail, see discussion at: JDBCDatabaseMetaData.

Specified by:

getCatalogName in interface ResultSetMetaData

Parameters:

column - the first column is 1, the second is 2, ...

Returns:

the name of the catalog for the table in which the given column appears or "" if not applicable

Throws:

SQLException - if a database access error occurs

getColumnType

public int getColumnType(int column)
                  throws SQLException

Retrieves the designated column's SQL type.

HSQLDB-Specific Information:

This reports the SQL type code of the column. For time and timestamp types that are WITH TIME ZONE, the values as the SQL Standard CLI codes.

Specified by:

getColumnType in interface ResultSetMetaData

Parameters:

column - the first column is 1, the second is 2, ...

Returns:

SQL type from java.sql.Types

Throws:

SQLException - if a database access error occurs

See Also:

Types

getColumnTypeName

public String getColumnTypeName(int column)
                         throws SQLException

Retrieves the designated column's database-specific type name.

Specified by:

getColumnTypeName in interface ResultSetMetaData

Parameters:

column - the first column is 1, the second is 2, ...

Returns:

type name used by the database. If the column type is a user-defined type, then a fully-qualified type name is returned.

Throws:

SQLException - if a database access error occurs

isReadOnly

public boolean isReadOnly(int column)
                   throws SQLException

Indicates whether the designated column is definitely not writable.

HSQLDB-Specific Information:

From 2.0 this method returns true if the ResultSet is not updatable or the column in question is not updatable.

Specified by:

isReadOnly in interface ResultSetMetaData

Parameters:

column - the first column is 1, the second is 2, ...

Returns:

true if so; false otherwise

Throws:

SQLException - if a database access error occurs

isWritable

public boolean isWritable(int column)
                   throws SQLException

Indicates whether it is possible for a write on the designated column to succeed.

HSQLDB-Specific Information:

From 2.0 this method returns false if the ResultSet is not updatable or the column in question is not updatable.

Specified by:

isWritable in interface ResultSetMetaData

Parameters:

column - the first column is 1, the second is 2, ...

Returns:

true if so; false otherwise

Throws:

SQLException - if a database access error occurs

isDefinitelyWritable

public boolean isDefinitelyWritable(int column)
                             throws SQLException

Indicates whether a write on the designated column will definitely succeed.

HSQLDB-Specific Information:

From 2.0 this method returns false if the ResultSet is not updatable or the column in question is not updatable.

Specified by:

isDefinitelyWritable in interface ResultSetMetaData

Parameters:

column - the first column is 1, the second is 2, ...

Returns:

true if so; false otherwise

Throws:

SQLException - if a database access error occurs

getColumnClassName

public String getColumnClassName(int column)
                          throws SQLException

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. ResultSet.getObject may return a subclass of the class returned by this method.

HSQLDB-Specific Information:

HSQLDB 2.0 fully supports this feature.

For columns of type OTHER, there is no specific class name and java.lang.Object is returned.

Specified by:

getColumnClassName in interface ResultSetMetaData

Parameters:

column - the first column is 1, the second is 2, ...

Returns:

the fully-qualified name of the class in the Java programming language that would be used by the method ResultSet.getObject to retrieve the value in the specified column. This is the class name used for custom mapping.

Throws:

SQLException - if a database access error occurs

Since:

JDK 1.2

unwrap

public <T> T unwrap(Class<T> iface)
             throws SQLException

Returns an object that implements the given interface to allow access to non-standard methods, or standard methods not exposed by the proxy. If the receiver implements the interface then the result is the receiver or a proxy for the receiver. If the receiver is a wrapper and the wrapped object implements the interface then the result is the wrapped object or a proxy for the wrapped object. Otherwise return the the result of calling unwrap recursively on the wrapped object or a proxy for that result. If the receiver is not a wrapper and does not implement the interface, then an SQLException is thrown.

Specified by:

unwrap in interface Wrapper

Parameters:

iface - A Class defining an interface that the result must implement.

Returns:

an object that implements the interface. May be a proxy for the actual implementing object.

Throws:

SQLException - If no object found that implements the interface

Since:

JDK 1.6

isWrapperFor

public boolean isWrapperFor(Class<?> iface)
                     throws SQLException

Returns true if this either implements the interface argument or is directly or indirectly a wrapper for an object that does. Returns false otherwise. If this implements the interface then return true, else if this is a wrapper then return the result of recursively calling isWrapperFor on the wrapped object. If this does not implement the interface and is not a wrapper, return false. This method should be implemented as a low-cost operation compared to unwrap so that callers can use this method to avoid expensive unwrap calls that may fail. If this method returns true then calling unwrap with the same argument should succeed.

Specified by:

isWrapperFor in interface Wrapper

Parameters:

iface - a Class defining an interface.

Returns:

true if this implements the interface or directly or indirectly wraps an object that does.

Throws:

SQLException - if an error occurs while determining whether this is a wrapper for an object with the given interface.

Since:

JDK 1.6

toString

public String toString()

Returns a string representation of the object.

The string consists of the name of the class of which the object is an instance, the at-sign character `@', the unsigned hexadecimal representation of the hash code of the object and a comma-delimited list of this object's indexed attributes, enclosed in square brackets.

Overrides:

toString in class Object

Returns:

a string representation of the object.