StringBuffer QuerySQL = new StringBuffer();
StringBuffer EmptyQuerySQL = new StringBuffer();
StringBuffer chekexistSQL = new StringBuffer();
StringBuffer UptdateSQL = new StringBuffer();
stmt = conn.createStatement();
chekexistSQL.append("SELECT * FROM ").append(tableName).append(
" WHERE ").append(colKey).append("=").append("'").append(
keyName).append("'");
EmptyQuerySQL.append("INSERT INTO ").append(tableName).append("(")
.append(colKey).append(",").append(blobName).append(
") VALUES (").append("'").append(keyName).append(
"',empty_blob()").append(")");
UptdateSQL.append("UPDATE ").append(tableName).append(" SET ")
.append(blobName).append("=empty_blob() where ").append(colKey).append("='").append(keyName).append("'");
QuerySQL.append("SELECT ").append(blobName).append(" FROM ")
.append(tableName).append(" ").append(" WHERE ").append(
colKey).append("=").append("'").append(keyName)
.append("'").append(" FOR UPDATE");
result = stmt.executeQuery(chekexistSQL.toString());
if (!result.next()) {
/* 插入空的附件 sql 中包含empty_blob() */
stmt.executeUpdate(UptdateSQL.toString());