Multiple queries executed in java in single statement

ghz 1years ago ⋅ 2990 views

Question

Hi I was wondering if it is possible to execute something like this using JDBC as it currently provides an exception even though it is possible in the MySQL query browser.

"SELECT FROM * TABLE;INSERT INTO TABLE;"

While I do realize that it is possible with having the SQL query string being split and the statement executed twice but I was wondering if there is a one time approach for this.

    String url = "jdbc:mysql://localhost:3306/";
    String dbName = "databaseinjection";
    String driver = "com.mysql.jdbc.Driver";
    String sqlUsername = "root"; 
    String sqlPassword = "abc";

    Class.forName(driver).newInstance();

    connection = DriverManager.getConnection(url+dbName, sqlUsername, sqlPassword);

Answer

I was wondering if it is possible to execute something like this using JDBC.

"SELECT * FROM TABLE;INSERT INTO TABLE;"

Yes it is possible. There are two ways, as far as I know. They are

  1. By setting database connection property to allow multiple queries, separated by a semi-colon by default.
  2. By calling a stored procedure that returns cursors implicit.

Following examples demonstrate the above two possibilities.

Example 1 : ( To allow multiple queries ):

While sending a connection request, you need to append a connection property allowMultiQueries=true to the database url. This is additional connection property to those if already exists some, like autoReConnect=true, etc.. Acceptable values for allowMultiQueries property are true, false, yes, and no. Any other value is rejected at runtime with an SQLException.

String dbUrl = "jdbc:mysql:///test?allowMultiQueries=true";

Unless such instruction is passed, an SQLException is thrown.

You have to use execute( String sql ) or its other variants to fetch results of the query execution.

boolean hasMoreResultSets = stmt.execute( multiQuerySqlString );

To iterate through and process results you require following steps:

READING_QUERY_RESULTS: // label  
    while ( hasMoreResultSets || stmt.getUpdateCount() != -1 ) {  
        if ( hasMoreResultSets ) {  
            Resultset rs = stmt.getResultSet();
            // handle your rs here
        } // if has rs
        else { // if ddl/dml/...
            int queryResult = stmt.getUpdateCount();  
            if ( queryResult == -1 ) { // no more queries processed  
                break READING_QUERY_RESULTS;  
            } // no more queries processed  
            // handle success, failure, generated keys, etc here
        } // if ddl/dml/...

        // check to continue in the loop  
        hasMoreResultSets = stmt.getMoreResults();  
    } // while results

Example 2 : Steps to follow:

  1. Create a procedure with one or more select, and DML queries.
  2. Call it from java using CallableStatement.
  3. You can capture multiple ResultSets executed in procedure.
    DML results can't be captured but can issue another select
    to find how the rows are affected in the table.

Sample table and procedure :

mysql> create table tbl_mq( i int not null auto_increment, name varchar(10), primary key (i) );
Query OK, 0 rows affected (0.16 sec)

mysql> delimiter //
mysql> create procedure multi_query()
    -> begin
    ->  select count(*) as name_count from tbl_mq;
    ->  insert into tbl_mq( names ) values ( 'ravi' );
    ->  select last_insert_id();
    ->  select * from tbl_mq;
    -> end;
    -> //
Query OK, 0 rows affected (0.02 sec)
mysql> delimiter ;
mysql> call multi_query();
+------------+
| name_count |
+------------+
|          0 |
+------------+
1 row in set (0.00 sec)

+------------------+
| last_insert_id() |
+------------------+
|                3 |
+------------------+
1 row in set (0.00 sec)

+---+------+
| i | name |
+---+------+
| 1 | ravi |
+---+------+
1 row in set (0.00 sec)

Query OK, 0 rows affected (0.00 sec)

Call Procedure from Java :

CallableStatement cstmt = con.prepareCall( "call multi_query()" );  
boolean hasMoreResultSets = cstmt.execute();  
READING_QUERY_RESULTS:  
    while ( hasMoreResultSets ) {  
        Resultset rs = stmt.getResultSet();
        // handle your rs here
    } // while has more rs
#mysql