Develop Reference

Sqlite-JDBC update with LIMIT clause?

I am trying to use the update query with the LIMIT clause using sqlite-JDBC.
Let's say there are 100 bob's in the table but I only want to update one of the records.
Sample code:
String name1 = "bob";
String name2 = "alice";
String updateSql = "update mytable set user = :name1 " +
"where user is :name2 " +
"limit 1";
try (Connection con = sql2o.open()) {
con.createQuery(updateSql)
.addParameter("bob", name1)
.addParameter("alice", name2)
.executeUpdate();
} catch(Exception e) {
e.printStackTrace();
}
I get an error:
org.sql2o.Sql2oException: Error preparing statement - [SQLITE_ERROR] SQL error or missing database (near "limit": syntax error)
Using
sqlite-jdbc 3.31
sql2o 1.6 (easy database query library)
The flag:
SQLITE_ENABLE_UPDATE_DELETE_LIMIT
needs to be set to get the limit clause to work with the update query.
I know the SELECT method works with the LIMIT clause but I would need 2 queries to do this task; SELECT then UPDATE.
If there is no way to get LIMIT to work with UPDATE then I will just use the slightly more messy method of having a query and sub query to get things to work.
Maybe there is a way to get sqlite-JDBC to use an external sqlite engine outside of the integrated one, which has been compiled with the flag set.
Any help appreciated.

You can try this query instead:
UPDATE mytable SET user = :name1
WHERE ROWID = (SELECT MIN(ROWID)
FROM mytable
WHERE user = :name2);
ROWID is a special column available in all tables (unless you use WITHOUT ROWID)

SQL Update field without unique index fields

I have table without unique index tuples, lets say table has records
A->B->Status
A->C->Status
A->B->Status
A->B->Status
A->C->Status
I am getting first and second record, processing them. After then I want to update only these two records
how can I make this process possible at java application layer?
Since there is not any unique index tupples I cannot use update SQL with proper WHERE clause
Using
Spring 3.XX
Oracle 11g

I think you may try to use ROWID pseudocolumn.
For each row in the database, the ROWID pseudocolumn returns the address of the row. Oracle Database rowid values contain information necessary to locate a row:
The data object number of the object
The data block in the datafile in which the row resides
The position of the row in the data block (first row is 0)
The datafile in which the row resides (first file is 1). The file
number is relative to the tablespace.
Usually, a rowid value uniquely identifies a row in the database. However, rows in different tables that are stored together in the same cluster can have the same rowid.
SELECT ROWID, last_name
FROM employees
WHERE department_id = 20;
The rowid for the row stays the same, even when the row migrates.

You can solve this issue by using updatable resultsets. This feature relies on rowid to perform all modifications (delete/update/insert).
This is a excerpt highlighting the feature itself:
String sqlString = "SELECT EmployeeID, Name, Office " +
" FROM employees WHERE EmployeeID=1001";
try {
stmt = con.createStatement(
ResultSet.TYPE_SCROLL_SENSITIVE,
ResultSet.CONCUR_UPDATABLE);
ResultSet rs = stmt.executeQuery(sqlString);
//Check the result set is an updatable result set
int concurrency = rs.getConcurrency();
if (concurrency == ResultSet.CONCUR_UPDATABLE) {
rs.first();
rs.updateString("Office", "HQ222");
rs.updateRow();
} else {
System.out.println("ResultSet is not an updatable result set.");
}
rs.close();
} catch(SQLException ex) {
System.err.println("SQLException: " + ex.getMessage());
}
Here is a complete example.

JDBC Return generated key or existing key

I have a table with unique index to eliminate duplicates (simplified example)
CREATE TABLE `domain` (
`id` INT(10) UNSIGNED NOT NULL AUTO_INCREMENT,
`subdomain` VARCHAR(255) NOT NULL,
`domain` VARCHAR(63) NOT NULL,
`zone` VARCHAR(63) NOT NULL,
PRIMARY KEY (`id`),
UNIQUE INDEX `UNIQUE` (`subdomain` ASC, `domain` ASC, `zone` ASC),
ENGINE = InnoDB;
I insert a lot of rows and i need to get primary keys returned (for other one-to-many inserts).
My problem is, that I insert a lot of duplicates and I need those keys returned too.
This is my solution which works, but isn't there more simple solution? With this I cannot use batch inserts and I want this to be most efficient.
PreparedStatement selectDomain = connection.prepareStatement("SELECT id FROM domain WHERE subdomain = ? AND domain = ? AND zone = ?");
PreparedStatement insertDomain = connection.prepareStatement("INSERT INTO domain(subdomain, domain, zone) VALUES (?,?,?)", Statement.RETURN_GENERATED_KEYS);
public int insertDomain(String subdomain, String domain, String zone) throws SQLException {
int domainId = 0;
selectDomain.setString(1, subdomain);
selectDomain.setString(2, domain);
selectDomain.setString(3, zone);
ResultSet resultSet = selectDomain.executeQuery();
if (resultSet.next()) {
domainId = resultSet.getInt(1);
} else {
insertDomain.setString(1, subdomain);
insertDomain.setString(2, subdomain);
insertDomain.setString(3, subdomain);
insertDomain.executeUpdate();
resultSet = insertDomain.getGeneratedKeys();
if (resultSet.next()) {
domainId = resultSet.getInt(1);
}
}
selectDomain.clearParameters();
insertDomain.clearParameters();
}

As I understand its not so easy approach for using batch execution. Your apporach is the best way to get the auto generated keys. There are few limitations of JDBC driver and it varies version to version, where getGeneratedKeys() works for single entry.
Please look into below links, it may help you :-
How to get generated keys from JDBC batch insert in Oracle?
http://docs.oracle.com/database/121/JJDBC/jdbcvers.htm#JJDBC28099

You could modify your INSERT to be something like this:
INSERT INTO domain (subdomain, domain, zone)
SELECT $subdomain, $domain, $zone
FROM domain
WHERE NOT EXISTS(
SELECT subdomain, domain, zone
FROM domain d
WHERE d.subdomain= $subdomain and d.domain=$domain and d.zone=$zone
)
LIMIT 1
Where $subdomain, $domain, $zone are the tag (properly quoted or as a placeholder of course) that you want to add if it isn't already there. This approach won't even trigger an INSERT (and the subsequent autoincrement wastage) if the tag is already there. You could probably come up with nicer SQL than that but the above should do the trick.
If your table is properly indexed then the extra SELECT for the existence check will be fast and the database is going to have to perform that check anyway.

Deciding addition or updation

I need to add a record if already a record with the primary key doesn't exist; otherwise existing record is to be updated. For this I am querying the db with the primary key. If no record exist, I am adding; otherwise updating. I am coding this in java using raw JDBC.
Is there a better way to do this?

insert … select … where not exist
INSERT INTO ... VALUES ... ON duplicate KEY UPDATE id = id
REPLACE INTO ... SELECT ... FROM ...

The most soft way to do this is to use special query INSERT ... ON DUPLICATE KEY UPDATE query in My Sql. It is much more effective than check is conflict exist on the application side.
Code snippet for example:
PreparedStatement statement = null;
try {
statement = connection.prepareStatement(
"INSERT INTO table (a,b,c) VALUES (?,?,?) ON DUPLICATE KEY UPDATE c=?;"
);
int paramIndex = 1;
statement.setInt(parameterIndex++, primaryKeyValue);
statement.setInt(parameterIndex++, secondValue);
statement.setInt(parameterIndex++, thirdValue);
statement.setInt(parameterIndex++, thirdValue);
int updatedCount = statement.executeUpdate();
} finally {
statement.close();
}

Another way would be REPLACE INTO which takes the same syntax as INSERT but removes the old entry when the primary key already exists before inserting.

The simplest and the most general way is to count the record before insert/update.
Pseudo Code:
SELECT COUNT(*) as recordCount FROM mytable WHERE keyField = ?
if (recordCount > 0) {
UPDATE mytable SET value1=? WHERE keyField = ?
} else {
INSERT INTO mytable (keyField, value1) VALUES (?, ?)
}

SQL query to select tablename

I want to get all database table names that ends with _tbl like xyz_tbl, pqr_tbl,etc..
in mysql using java.pls help me.. currently my query retreives all tablename but i jst want table names that ends with _tbl.
My code is...
public List selectTable() {
List tableNameList= new ArrayList();
try {
DatabaseMetaData dbm = c.conn.getMetaData();
String[] types = {"TABLE"};
c.rs = dbm.getTables(null, null, "%", types);
while (c.rs.next()) {
tableNameList.add(c.rs.getString("TABLE_NAME"));
}
} catch(Exception e) {
System.out.println(e.toString());
}
return tableNameList;
}

Did you try using a different table name pattern?
You can try this: -
c.rs = dbm.getTables(null, null, "%_tbl", types);

You can use mysql query
show tables from tablename like '%_tbl';

I am unable to reply to Rohit's post. his answer looks correct.
If you do to JDK documentation for DatabaseMetaData's getTables method following is the signature and documentation comment.
ResultSet getTables(String catalog, String schemaPattern, String tableNamePattern,
String[] types) throws SQLException
Parameters:
catalog - a catalog name; must match the catalog name as it is stored
in the database; "" retrieves those without a catalog; null means that
the catalog name should not be used to narrow the search
schemaPattern
- a schema name pattern; must match the schema name as it is stored in the database; "" retrieves those without a schema; null means that the
schema name should not be used to narrow the search tableNamePattern -
a table name pattern; must match the table name as it is stored in the
database types - a list of table types, which must be from the list of
table types returned from getTableTypes(),to include; null returns all
types
In this case using %_tbl should work.

Use the String.endsWith() method to check if the table name ends with "_tbl".
For example inside your while loop:
while (c.rs.next())
{
String tableName = c.rs.getString("TABLE_NAME");
if(tableName.endsWith("_tbl"))
{
tableNameList.add(c.rs.getString("TABLE_NAME"));
}
}