如何从存储过程返回值

Question

I have a MySql procedure that gets some input arguments and as a result selects a single value like this:

declare rez int;
///
...some other code...
///
select rez;

Now, i want to call that stored procedure from another stored procedure and obtain "selected" value. I tried something like this:

declare myVar int;
set myVar = call existingStoredProcedure();

but it won't do. How should i do this? I was googling for the solution and all solutions i found begin with something like "create >existingStoredProcedure< with OUT param". For me that's not an option - "existingStoredProcedure" can't be changed as it's being used in many parts of the application so adding another parameter would ask for a lot of changes i presume.

Is there a way to return a value without adding "out" parameter? I'm a Java programmer so it would be very nice if mysql stored procedure could just "return" selected rows and values to any entity that placed a call :)

Answer 1

If a procedure just executes a select statement, then you can read the results into an instance of ResultSet .

CallableStatement cst = con.prepareCall( "{call sql_procedureName()}" );
ResultSet rs = cst.executeQuery();

Working Example :

Let us say, you have a stored procedure that returns current date and current day name.

drop procedure if exists today;
create procedure today() 
    select @dt:=current_date as today, dayname( @dt ) as dayname;

Now, call the same from JAVA program.

CallableStatement cst = con.prepareCall( "{call today()}" );

ResultSet rs = cst.executeQuery();
ResultSetMetaData  rsmd = rs.getMetaData();
int columnCount = rsmd.getColumnCount();
System.out.println( "Column Count: " + columnCount );
for ( int i = 1; i <= columnCount; i++ ) {
    System.out.print( ( i == 1 ? "Column Names: " : ", " ) 
                        + rsmd.getColumnLabel( i ) );
} // for each column
System.out.println();

int rowNumber = 1;
while( rs.next() ) {
    for ( int i = 1; i <= columnCount; i++ ) {
        System.out.print( ( i == 1 ? ( "Record " + rowNumber++ + ": " ) : ", " ) 
                         + rsmd.getColumnLabel( i ) + ": " + rs.getString( i ) );
    } // for each column
    System.out.println();
} // while rs

Output :

Column Count: 2
Column Names: today, dayname
Record 1: today: 2014-04-03, dayname: Thursday

Refer to :

• java.sql.CallableStatement
  • A CallableStatement can return one ResultSet object or multiple ResultSet objects.