RE: best way to check for the exsitence of a table
Rick, thank you for your prompt and helpful response.
Regards,
Pavel.
-Original Message-
From: Rick Hillegas [mailto:rick.hille...@oracle.com]
Sent: Tuesday, May 22, 2012 3:33 PM
To: derby-user@db.apache.org
Subject: Re: best way to check for the exsitence of a table
Hi Pavel,
Querying the metadata as you suggest is a good approach. You will want to
adjust the arguments to DatabaseMetaData.getTables() however. The arguments in
your example may find false matches in other schemas and with tables created
with double-quoted names. The following example may help you adjust the
arguments to getTable():
public class z
{
public static voidmain( String... args ) throws Exception
{
Connection conn = DriverManager.getConnection(
"jdbc:derby:memory:db;create=true" );
conn.prepareStatement( "create table myTable( a int )" ).execute();
DatabaseMetaDatadbmd = conn.getMetaData();
ResultSet rs;
rs = dbmd.getTables( null, "APP", "MYTABLE", new String[] { "TABLE" }
);
System.out.println( "Table 'MYTABLE' exists = " + rs.next() );
rs = dbmd.getTables( null, "APP", "mytable", new String[] { "TABLE" }
);
System.out.println( "Table 'mytable' exists = " + rs.next() );
}
}
Hope this helps,
-Rick
On 5/22/12 11:33 AM, Pavel Bortnovskiy wrote:
>
> Hello:
>
> When reading derby docs, I noticed that the functionWwdUtils.wwdChk4Tablein
> 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;
>
> }
>
> }
>
>
> Jefferies archives and monitors outgoing and incoming
> e-mail. The contents of this email, including any
> attachments, are confidential to the ordinary user of the
> email address to which it was addressed. If you are not
> the addressee of this email you may not copy, forward,
> disclose or otherwise use it or any part of it in any form
>
Re: best way to check for the exsitence of a table
Hi Pavel,
Querying the metadata as you suggest is a good approach. You will want
to adjust the arguments to DatabaseMetaData.getTables() however. The
arguments in your example may find false matches in other schemas and
with tables created with double-quoted names. The following example may
help you adjust the arguments to getTable():
public class z
{
public static voidmain( String... args ) throws Exception
{
Connection conn = DriverManager.getConnection(
"jdbc:derby:memory:db;create=true" );
conn.prepareStatement( "create table myTable( a int )" ).execute();
DatabaseMetaDatadbmd = conn.getMetaData();
ResultSet rs;
rs = dbmd.getTables( null, "APP", "MYTABLE", new String[] {
"TABLE" } );
System.out.println( "Table 'MYTABLE' exists = " + rs.next() );
rs = dbmd.getTables( null, "APP", "mytable", new String[] {
"TABLE" } );
System.out.println( "Table 'mytable' exists = " + rs.next() );
}
}
Hope this helps,
-Rick
On 5/22/12 11:33 AM, Pavel Bortnovskiy wrote:
Hello:
When reading derby docs, I noticed that the functionWwdUtils.wwdChk4Tablein
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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best way to check for the exsitence of a table
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;
}
}
Jefferies archives and monitors outgoing and incoming e-mail. The contents of
this email, including any attachments, are confidential to the ordinary user of
the email address to which it was addressed. If you are not the addressee of
this email you may not copy, forward, disclose or otherwise use it or any part
of it in any form whatsoever. This email may be produced at the request of
regulators or in connection with civil litigation. Jefferies accepts no
liability for any errors or omissions arising as a result of transmission. Use
by other than intended recipients is prohibited. In the United Kingdom,
Jefferies operates as Jefferies International Limited; registered in England:
no. 1978621; registered office: Vintners Place, 68 Upper Thames Street, London
EC4V 3BJ. Jefferies International Limited is authorised and regulated by the
Financial Services Authority.
