11.5.4 DatabaseMetaData

Connection.getMetaData() returns information about the driver, server, schema objects, and JDBC capabilities. Result columns use JDBC standard names and ordering; read columns by name rather than numeric position.

import java.sql.DatabaseMetaData;

DatabaseMetaData metadata = connection.getMetaData();

System.out.println(metadata.getDriverName());
System.out.println(metadata.getDriverVersion());
System.out.println(metadata.getDatabaseProductName());
System.out.println(metadata.getDatabaseProductVersion());

Tables and Views

try (ResultSet tables = metadata.getTables(
         null, null, "%", new String[] {"TABLE", "VIEW"})) {
    while (tables.next()) {
        System.out.printf("%s %s%n",
            tables.getString("TABLE_NAME"),
            tables.getString("TABLE_TYPE"));
    }
}

getTables() distinguishes TABLE from VIEW. See REMARKS for the specific Machbase table type. Applications should use standard column names instead of depending on column positions.

Columns

try (ResultSet columns = metadata.getColumns(
         null, null, "SENSOR_TX", "%")) {
    while (columns.next()) {
        System.out.printf(
            "%s %s size=%d nullable=%s%n",
            columns.getString("COLUMN_NAME"),
            columns.getString("TYPE_NAME"),
            columns.getInt("COLUMN_SIZE"),
            columns.getString("IS_NULLABLE"));
    }
}

NULLABLE returns a numeric constant; IS_NULLABLE returns YES, NO, or an empty string. PRIMARY KEY columns in LOOKUP and VOLATILE tables return columnNoNulls and NO even without an explicit NOT NULL clause.

DECIMAL_DIGITS and NUM_PREC_RADIX are SQL NULL for columns without these numeric attributes, such as VARCHAR, DATETIME, BINARY, BLOB, and CLOB. Check NULL with getObject() or wasNull() instead of relying on a 0 returned by getInt().

Primary Keys and Indexes

try (ResultSet keys = metadata.getPrimaryKeys(
         null, null, "SENSOR_TX")) {
    while (keys.next()) {
        System.out.printf("%s position=%d%n",
            keys.getString("COLUMN_NAME"),
            keys.getShort("KEY_SEQ"));
    }
}

try (ResultSet indexes = metadata.getIndexInfo(
         null, null, "SENSOR_TX", false, false)) {
    while (indexes.next()) {
        System.out.printf("%s %s%n",
            indexes.getString("INDEX_NAME"),
            indexes.getString("COLUMN_NAME"));
    }
}

Do not infer PRIMARY KEY membership from ResultSetMetaData.isNullable(). Use getPrimaryKeys() and getIndexInfo().

For a direct column in a SELECT result, the Machbase JDBC extension MachResultSetMetaData.isPrimaryKey(column) reports PRIMARY KEY membership.

import com.machbase.jdbc.MachResultSetMetaData;

try (ResultSet result = statement.executeQuery(
         "SELECT ID, ID + 1 AS ID_EXPR FROM SENSOR_TX")) {
    MachResultSetMetaData resultMetadata =
        (MachResultSetMetaData) result.getMetaData();
    System.out.println(resultMetadata.isPrimaryKey(1)); // true or false
    System.out.println(resultMetadata.isPrimaryKey(2)); // expression: false
}

getPrimaryKeys() reads primary keys from the table catalog; isPrimaryKey() reads column metadata for the current SELECT result. An older server or SDK may return false for the result-column primary key flag.

Schema and Type Information

The following methods return ResultSets in the standard JDBC format:

• getSchemas(), getCatalogs(), getTableTypes()
• getTypeInfo()
• getTables(), getColumns()
• getPrimaryKeys(), getIndexInfo()

Unsupported optional metadata queries may return an empty ResultSet with standard columns instead of null or a nonstandard ResultSet. Check the capability methods before using a feature.

if (metadata.supportsSavepoints()) {
    // Use savepoints only where supported.
}

catalog

Connection.getCatalog() and setCatalog() manage the current catalog value exposed by the driver. Catalog arguments to metadata methods filter requests against this value.

String initialCatalog = connection.getCatalog();
connection.setCatalog(initialCatalog);

Returning a logical Connection to a pool restores the initial catalog determined by the URL. Do not reuse a DatabaseMetaData object from a previous connection lease in the next lease.

Check Supported Features

Machbase JDBC capability methods reflect actual support. For example, check transaction isolation levels, ResultSet types, savepoints, generated keys, and multiple open results as follows:

System.out.println(metadata.supportsTransactions());
System.out.println(metadata.supportsTransactionIsolationLevel(
    Connection.TRANSACTION_SERIALIZABLE));
System.out.println(metadata.supportsResultSetType(
    ResultSet.TYPE_FORWARD_ONLY));
System.out.println(metadata.supportsSavepoints());
System.out.println(metadata.supportsGetGeneratedKeys());
System.out.println(metadata.supportsMultipleOpenResults());

A false result from Driver.jdbcCompliant() is separate from support for individual JDBC APIs. Applications should check the features they require.

When connected to a Standard Edition server that supports ROWID, supportsGetGeneratedKeys() returns true, and getRowIdLifetime() returns ROWID_VALID_OTHER. On an unsupported server or Cluster Edition, they return false and ROWID_UNSUPPORTED, respectively. See ROWID and INSERT Result IDs for examples.