如何使用 JDBC 删除 Apache Derby DB 架构中的所有表？
Shimi Bandiel
问问题
31679 次
11 回答
7
感谢博客：
第1步：
运行 SQL 语句，但不要忘记在以下 2 次出现中将模式名称“APP”替换为您的模式名称：
SELECT
'ALTER TABLE '||S.SCHEMANAME||'.'||T.TABLENAME||' DROP CONSTRAINT '||C.CONSTRAINTNAME||';'
FROM
SYS.SYSCONSTRAINTS C,
SYS.SYSSCHEMAS S,
SYS.SYSTABLES T
WHERE
C.SCHEMAID = S.SCHEMAID
AND
C.TABLEID = T.TABLEID
AND
S.SCHEMANAME = 'APP'
UNION
SELECT 'DROP TABLE ' || schemaname ||'.' || tablename || ';'
FROM SYS.SYSTABLES
INNER JOIN SYS.SYSSCHEMAS ON SYS.SYSTABLES.SCHEMAID = SYS.SYSSCHEMAS.SCHEMAID
where schemaname='APP';
第2步：
上述执行的结果是一组 SQL 语句，将它们复制到 SQL 编辑器，执行它们，然后删除约束和表。
于 2014-04-06T04:58:54.123 回答
5
有关执行此操作的实际代码，请检查Derby 分发版的 Derby 测试套件部分中的CleanDatabaseTestSetup.java 。
于 2009-11-14T15:32:05.087 回答
3
在java中执行一个小方法，在其中执行
DROP TABLE [tablename]
tablename是通过参数传递的。
还有另一种方法，您可以在其中循环由查询形成的记录集
SELECT tablename FROM SYSTABLES
调用第一种方法。
于 2008-10-05T09:58:09.727 回答
1
我认为大多数数据库提供商不允许 DROP TABLE * （或类似的）。
我认为最好的方法是显示表，然后通过结果集在循环中遍历每个删除。
HTH。
于 2008-10-05T09:44:49.160 回答
0
JDBC 允许您以与数据库无关的方式解决您的任务：
- 打开连接
- 获取数据库元数据
- 使用它列出数据库JavaDoc中的所有表
- 遍历结果集并为每个表触发 DROP TABLE
于 2008-10-05T10:31:08.613 回答
0
- 您必须从 Derby DB 系统目录生成模式和表名。
- 按关系对所有表进行排序。
- 生成删除所有表的java语句
- 使用 autoCommit() 方法并将此方法设置为 false。出错时用于手动提交或回滚事务。
- 运行你的java进程。祝你好运。
于 2008-10-05T15:48:51.047 回答
0
一个更简单的解决方案是使用 JDBC 运行“drop database foo”然后“create database foo”。但是，这将导致数据库中的所有对象都被删除（即不仅仅是表）。
于 2008-10-05T23:20:04.007 回答
0
如果您从命令提示符而不是通过 JDBC 工作，这应该可以帮助您入门。
SELECT 'DROP TABLE ' || schemaname ||'.' || tablename || ';'
FROM SYS.SYSTABLES
INNER JOIN SYS.SYSSCHEMAS ON SYS.SYSTABLES.SCHEMAID = SYS.SYSSCHEMAS.SCHEMAID
;
于 2012-12-18T07:55:28.263 回答
0
一个简单的解决方案是右键单击-> 断开连接，然后删除包含数据库的文件夹并重新连接。
于 2013-08-23T07:57:16.490 回答
0
从http://squirrel-sql.sourceforge.net/下载 Squirrel SQL
连接到数据库。
展开表节点。
选择要删除的表。
右键单击并选择 -> 脚本 -> 删除表脚本
运行生成的查询
您甚至可以选择删除记录来清空选定的表。
于 2013-11-17T15:41:20.003 回答
0
对于那些希望以编程方式删除所有模式而不必每次都手动复制粘贴 SQL 的人，这里是从org.apache.derbyTesting.junit.CleanDatabaseTestSetup和org.apache.derbyTesting.junit.JDBC中提取的代码。你只需调用 dropAllSchemas(connection);
public static void dropAllSchemas(Connection conn) throws SQLException {
DatabaseMetaData dmd = conn.getMetaData();
SQLException sqle = null;
// Loop a number of arbitary times to catch cases
// where objects are dependent on objects in
// different schemas.
for (int count = 0; count < 5; count++) {
// Fetch all the user schemas into a list
List<String> schemas = new ArrayList<String>();
ResultSet rs = dmd.getSchemas();
while (rs.next()) {
String schema = rs.getString("TABLE_SCHEM");
if (schema.startsWith("SYS"))
continue;
if (schema.equals("SQLJ"))
continue;
if (schema.equals("NULLID"))
continue;
schemas.add(schema);
}
rs.close();
// DROP all the user schemas.
sqle = null;
for (String schema : schemas) {
try {
dropSchema(dmd, schema);
} catch (SQLException e) {
sqle = e;
}
}
// No errors means all the schemas we wanted to
// drop were dropped, so nothing more to do.
if (sqle == null)
return;
}
throw sqle;
}
/**
* Constant to pass to DatabaseMetaData.getTables() to fetch
* just tables.
*/
public static final String[] GET_TABLES_TABLE = new String[] {"TABLE"};
/**
* Constant to pass to DatabaseMetaData.getTables() to fetch
* just views.
*/
public static final String[] GET_TABLES_VIEW = new String[] {"VIEW"};
/**
* Constant to pass to DatabaseMetaData.getTables() to fetch
* just synonyms.
*/
public static final String[] GET_TABLES_SYNONYM =
new String[] {"SYNONYM"};
/**
* Drop a database schema by dropping all objects in it
* and then executing DROP SCHEMA. If the schema is
* APP it is cleaned but DROP SCHEMA is not executed.
*
* TODO: Handle dependencies by looping in some intelligent
* way until everything can be dropped.
*
*
* @param dmd DatabaseMetaData object for database
* @param schema Name of the schema
* @throws SQLException database error
*/
public static void dropSchema(DatabaseMetaData dmd, String schema) throws SQLException{
Connection conn = dmd.getConnection();
Statement s = dmd.getConnection().createStatement();
// Triggers
PreparedStatement pstr = conn.prepareStatement(
"SELECT TRIGGERNAME FROM SYS.SYSSCHEMAS S, SYS.SYSTRIGGERS T "
+ "WHERE S.SCHEMAID = T.SCHEMAID AND SCHEMANAME = ?");
pstr.setString(1, schema);
ResultSet trrs = pstr.executeQuery();
while (trrs.next()) {
String trigger = trrs.getString(1);
s.execute("DROP TRIGGER " + escape(schema, trigger));
}
trrs.close();
pstr.close();
// Functions - not supported by JDBC meta data until JDBC 4
// Need to use the CHAR() function on A.ALIASTYPE
// so that the compare will work in any schema.
PreparedStatement psf = conn.prepareStatement(
"SELECT ALIAS FROM SYS.SYSALIASES A, SYS.SYSSCHEMAS S" +
" WHERE A.SCHEMAID = S.SCHEMAID " +
" AND CHAR(A.ALIASTYPE) = ? " +
" AND S.SCHEMANAME = ?");
psf.setString(1, "F" );
psf.setString(2, schema);
ResultSet rs = psf.executeQuery();
dropUsingDMD(s, rs, schema, "ALIAS", "FUNCTION");
// Procedures
rs = dmd.getProcedures((String) null,
schema, (String) null);
dropUsingDMD(s, rs, schema, "PROCEDURE_NAME", "PROCEDURE");
// Views
rs = dmd.getTables((String) null, schema, (String) null,
GET_TABLES_VIEW);
dropUsingDMD(s, rs, schema, "TABLE_NAME", "VIEW");
// Tables
rs = dmd.getTables((String) null, schema, (String) null,
GET_TABLES_TABLE);
dropUsingDMD(s, rs, schema, "TABLE_NAME", "TABLE");
// At this point there may be tables left due to
// foreign key constraints leading to a dependency loop.
// Drop any constraints that remain and then drop the tables.
// If there are no tables then this should be a quick no-op.
ResultSet table_rs = dmd.getTables((String) null, schema, (String) null,
GET_TABLES_TABLE);
while (table_rs.next()) {
String tablename = table_rs.getString("TABLE_NAME");
rs = dmd.getExportedKeys((String) null, schema, tablename);
while (rs.next()) {
short keyPosition = rs.getShort("KEY_SEQ");
if (keyPosition != 1)
continue;
String fkName = rs.getString("FK_NAME");
// No name, probably can't happen but couldn't drop it anyway.
if (fkName == null)
continue;
String fkSchema = rs.getString("FKTABLE_SCHEM");
String fkTable = rs.getString("FKTABLE_NAME");
String ddl = "ALTER TABLE " +
escape(fkSchema, fkTable) +
" DROP FOREIGN KEY " +
escape(fkName);
s.executeUpdate(ddl);
}
rs.close();
}
table_rs.close();
conn.commit();
// Tables (again)
rs = dmd.getTables((String) null, schema, (String) null,
GET_TABLES_TABLE);
dropUsingDMD(s, rs, schema, "TABLE_NAME", "TABLE");
// drop UDTs
psf.setString(1, "A" );
psf.setString(2, schema);
rs = psf.executeQuery();
dropUsingDMD(s, rs, schema, "ALIAS", "TYPE");
// drop aggregates
psf.setString(1, "G" );
psf.setString(2, schema);
rs = psf.executeQuery();
dropUsingDMD(s, rs, schema, "ALIAS", "DERBY AGGREGATE");
psf.close();
// Synonyms - need work around for DERBY-1790 where
// passing a table type of SYNONYM fails.
rs = dmd.getTables((String) null, schema, (String) null,
GET_TABLES_SYNONYM);
dropUsingDMD(s, rs, schema, "TABLE_NAME", "SYNONYM");
// sequences
if ( sysSequencesExists( conn ) )
{
psf = conn.prepareStatement
(
"SELECT SEQUENCENAME FROM SYS.SYSSEQUENCES A, SYS.SYSSCHEMAS S" +
" WHERE A.SCHEMAID = S.SCHEMAID " +
" AND S.SCHEMANAME = ?");
psf.setString(1, schema);
rs = psf.executeQuery();
dropUsingDMD(s, rs, schema, "SEQUENCENAME", "SEQUENCE");
psf.close();
}
// Finally drop the schema if it is not APP
if (!schema.equals("APP")) {
s.executeUpdate("DROP SCHEMA " + escape(schema) + " RESTRICT");
}
conn.commit();
s.close();
}
/**
* Return true if the SYSSEQUENCES table exists.
*/
private static boolean sysSequencesExists( Connection conn ) throws SQLException
{
PreparedStatement ps = null;
ResultSet rs = null;
try {
ps = conn.prepareStatement
(
"select count(*) from sys.systables t, sys.sysschemas s\n" +
"where t.schemaid = s.schemaid\n" +
"and ( cast(s.schemaname as varchar(128)))= 'SYS'\n" +
"and ( cast(t.tablename as varchar(128))) = 'SYSSEQUENCES'" );
rs = ps.executeQuery();
rs.next();
return ( rs.getInt( 1 ) > 0 );
}
finally
{
if ( rs != null ) { rs.close(); }
if ( ps != null ) { ps.close(); }
}
}
/**
* Escape a non-qualified name so that it is suitable
* for use in a SQL query executed by JDBC.
*/
public static String escape(String name)
{
StringBuffer buffer = new StringBuffer(name.length() + 2);
buffer.append('"');
for (int i = 0; i < name.length(); i++) {
char c = name.charAt(i);
// escape double quote characters with an extra double quote
if (c == '"') buffer.append('"');
buffer.append(c);
}
buffer.append('"');
return buffer.toString();
}
/**
* Escape a schema-qualified name so that it is suitable
* for use in a SQL query executed by JDBC.
*/
public static String escape(String schema, String name)
{
return escape(schema) + "." + escape(name);
}
/**
* DROP a set of objects based upon a ResultSet from a
* DatabaseMetaData call.
*
* TODO: Handle errors to ensure all objects are dropped,
* probably requires interaction with its caller.
*
* @param s Statement object used to execute the DROP commands.
* @param rs DatabaseMetaData ResultSet
* @param schema Schema the objects are contained in
* @param mdColumn The column name used to extract the object's
* name from rs
* @param dropType The keyword to use after DROP in the SQL statement
* @throws SQLException database errors.
*/
private static void dropUsingDMD(
Statement s, ResultSet rs, String schema,
String mdColumn,
String dropType) throws SQLException
{
String dropLeadIn = "DROP " + dropType + " ";
// First collect the set of DROP SQL statements.
ArrayList<String> ddl = new ArrayList<String>();
while (rs.next())
{
String objectName = rs.getString(mdColumn);
String raw = dropLeadIn + escape(schema, objectName);
if (
"TYPE".equals( dropType ) ||
"SEQUENCE".equals( dropType ) ||
"DERBY AGGREGATE".equals( dropType )
)
{ raw = raw + " restrict "; }
ddl.add( raw );
}
rs.close();
if (ddl.isEmpty())
return;
// Execute them as a complete batch, hoping they will all succeed.
s.clearBatch();
int batchCount = 0;
for (Iterator i = ddl.iterator(); i.hasNext(); )
{
Object sql = i.next();
if (sql != null) {
s.addBatch(sql.toString());
batchCount++;
}
}
int[] results;
boolean hadError;
try {
results = s.executeBatch();
//Assert.assertNotNull(results);
//Assert.assertEquals("Incorrect result length from executeBatch", batchCount, results.length);
hadError = false;
} catch (BatchUpdateException batchException) {
results = batchException.getUpdateCounts();
//Assert.assertNotNull(results);
//Assert.assertTrue("Too many results in BatchUpdateException", results.length <= batchCount);
hadError = true;
}
// Remove any statements from the list that succeeded.
boolean didDrop = false;
for (int i = 0; i < results.length; i++)
{
int result = results[i];
if (result == Statement.EXECUTE_FAILED)
hadError = true;
else if (result == Statement.SUCCESS_NO_INFO || result >= 0) {
didDrop = true;
ddl.set(i, null);
}
//else
//Assert.fail("Negative executeBatch status");
}
s.clearBatch();
if (didDrop) {
// Commit any work we did do.
s.getConnection().commit();
}
// If we had failures drop them as individual statements
// until there are none left or none succeed. We need to
// do this because the batch processing stops at the first
// error. This copes with the simple case where there
// are objects of the same type that depend on each other
// and a different drop order will allow all or most
// to be dropped.
if (hadError) {
do {
hadError = false;
didDrop = false;
for (ListIterator<String> i = ddl.listIterator(); i.hasNext();) {
String sql = i.next();
if (sql != null) {
try {
s.executeUpdate(sql);
i.set(null);
didDrop = true;
} catch (SQLException e) {
hadError = true;
}
}
}
if (didDrop)
s.getConnection().commit();
} while (hadError && didDrop);
}
}
PS：当我将我的数据库从支持 DROP ALL OBJECTS 的 H2 迁移到不支持 DROP ALL OBJECTS 的 Apache Derby 时，这段代码派上了用场（头痛）。我从 H2 迁移出来的唯一原因是它是一个完全在内存中的数据库，并且对于我的服务器的 RAM 来说太大了，所以我决定尝试 Apache Derby。H2 比 Derby 更容易、更人性化，我强烈推荐它。我很遗憾我买不起 RAM 来继续使用 H2。顺便说一句，对于那些受 Derby 缺乏 LIMIT 或 UPSERT 影响的人，请参阅这篇关于替换FETCH NEXT而不是 LIMIT 的文章以及关于正确使用MERGE INTO的这篇文章。
于 2022-01-14T04:24:40.613 回答