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From Pavel Bortnovskiy <pbortnovs...@jefferies.com>
Subject best way to check for the exsitence of a table
Date Tue, 22 May 2012 18:33:50 GMT
Hello:


When reading derby docs, I noticed that the function WwdUtils.wwdChk4Table in Derby demos
is implemented by executing an update on the table and then relying on the exception mechanism
to determine whether or not the table exists.



My approach was to execute DatabaseMetaData.getTables method (pls see implementation below)
and iterate through the resultset. I also wanted to assure case insensitivity.



Which method is more preferable from the point of efficiency and database operations (locks,
etc).

This code might be executed frequently and by multiple threads.



Thank you,

Pavel.



    public static boolean tableExists(final Connection connection, final String tableName)
throws SQLException {
        try {
            final DatabaseMetaData databaseMetaData = connection.getMetaData();
            final ResultSet resultSet = databaseMetaData.getTables(null, null, null, new String[]{"TABLE"});
            try {
                while (resultSet.next()) {
                    if (resultSet.getString("TABLE_NAME").equalsIgnoreCase(tableName)) {
                        return true;
                    }
                }
            } finally {
                connection.commit();
                resultSet.close();
            }
            return false;
        } catch (SQLException e) {
            Statement statement = null;
            try {
                final Connection c = Components.getMemoryDb().getConnection(true);
                statement = c.createStatement();
                final String select = "SELECT * FROM SYSCS_DIAG.LOCK_TABLE";
                final ResultSet resultSet = statement.executeQuery(select);
                final int cnt = resultSet.getMetaData().getColumnCount();
                final StringBuilder builder = new StringBuilder("Results of \"" + select +
"\":");
                while (resultSet.next()) {
                    builder.append("\n\t");
                    for (int i = 1; i <= cnt; i++) {
                        if (i > 1) {
                            builder.append(",");
                        }
                        builder.append(resultSet.getObject(i));
                    }
                }
                logger.info(builder.toString());
            } finally {
                if (statement != null) {
                    statement.close();
                }
            }
            throw e;
        }
    }
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