Programming with SQL Relay using the Perl DBI API

Establishing a Session

To use SQL Relay, you have to identify the connection that you intend to use.

#!/usr/bin/env perl

use DBI;

my $dbh=DBI->connect("DBI:SQLRelay:host=sqlrserver;port=9000;socket=/tmp/example.socket;tries=0;retrytime=1;debug=0","exampleuser","examplepassword");

... execute some queries ...

$dbh->disconnect;

The following connect string variables control attributes of the connection:

• host - The SQL Relay server to connect to.
• port - The port that the SQL Relay server is listening on. Either port or socket must be specified. If both are specified, socket will be preferred to port.
• socket - The socket that the SQL Relay server is listening on. Either port or socket must be specified. If both are specified, socket will be preferred to port.
• tries - If a connection fails, it will be retried this many times.
• retrytime - If a connection fails, it will be retried on this interval (in seconds).
• db - The database to switch to when logging into SQL Relay. May be left empty or omitted to accept the default database that SQL Relay is already connected to.
• debug - If this is set to 1 or to a file name then debug is enabled. If set to a file name then debug will be written to the file. If set to 1 then debug will be written to standard output. Defaults to 0.
• lazyconnect - By default, the SQL Relay client does "lazy connects". I.e. the connection to the SQL Relay server isn't established until the first query or other operation is run. This optimizes availability of the connection pool but is inconstent with most other database API's. Setting this parameter to 0 causes the connection to the SQL Relay server to be established immediately and the constructor to fail, returning undef, if the connection cannot be established. Defaults to 1.

In addition, the following connect string variables can be used to establish Kerberos or Active Directory encryption and authentication with the server:

Executing Queries

Call prepare() and execute() to run a query.

#!/usr/bin/env perl

use DBI;

my $dbh=DBI->connect("DBI:SQLRelay:host=sqlrserver;port=9000;socket=/tmp/example.socket;tries=0;retrytime=1;debug=0","exampleuser","examplepassword");

my $sth=$dbh->prepare("select * from user_tables");

$sth->execute();

... process the result set ...

$dbh->disconnect;

Commits and Rollbacks

If you need to execute a commit or rollback, you should use the commit() and rollback() methods rather than sending a "commit" or "rollback" query. There are two reasons for this. First, it's much more efficient to call the methods. Second, if you're writing code that can run on transactional or non-transactional databases, some non-transactional databases will throw errors if they receive a "commit" or "rollback" query, but by calling the commit() and rollback() methods you instruct the database connection daemon to call the commit and rollback API methods for that database rather than issuing them as queries. If the API's have no commit or rollback methods, the calls do nothing and the database throws no error.

Temporary Tables

Some databases support temporary tables. That is, tables which are automatically dropped or truncated when an application closes its connection to the database or when a transaction is committed or rolled back.

For databases which drop or truncate tables when a transaction is committed or rolled back, temporary tables work naturally.

However, for databases which drop or truncate tables when an application closes its connection to the database, there is an issue. Since SQL Relay maintains persistent database connections, when an application disconnects from SQL Relay, the connection between SQL Relay and the database remains, so the database does not know to drop or truncate the table. To remedy this situation, SQL Relay parses each query to see if it created a temporary table, keeps a list of temporary tables and drops (or truncates them) when the application disconnects from SQL Relay. Since each database has slightly different syntax for creating a temporary table, SQL Relay parses each query according to the rules for that database.

In effect, temporary tables should work when an application connects to SQL Relay in the same manner that they would work if the application connected directly to the database.

Catching Errors

If your calls to connect(), prepare() or execute() fail, you can catch the error in DBI->errstr.

#!/usr/bin/env perl

use DBI;

my $dbh=DBI->connect("DBI:SQLRelay:host=sqlrserver;port=9000;socket=/tmp/example.socket;tries=0;retrytime=1;debug=0","exampleuser","examplepassword")
        or die DBI->errstr;

my $sth=$dbh->prepare("select * from user_tables")
        or die DBI->errstr;

$sth->execute()
        or die DBI->errstr;

... process the result set ...

$dbh->disconnect;

Bind Variables

Programs rarely execute fixed queries. More often than not, some part of the query is dynamically generated. The Perl DBI API provides means for using bind variables in those queries.

Re-Binding and Re-Execution

A feature of the prepare/bind/execute paradigm is the ability to prepare, bind and execute a query once, then re-bind and re-execute the query over and over without re-preparing it. If your back-end database natively supports this paradigm, you can reap a substantial performance improvement.

#!/usr/bin/env perl

use DBI;

my $dbh=DBI->connect("DBI:SQLRelay:host=sqlrserver;port=9000;socket=/tmp/example.socket;tries=0;retrytime=1;debug=0","exampleuser","examplepassword");

my $sth=$dbh->prepare("select * from my_table where col1=:0 and col2=:1 and col3=:2");

$sth->execute(undef,"hello",1,1.1);

... process result set ...

$sth->execute(undef,"hi",2,2.2);

... process result set ...

$sth->execute(undef,"goodbye",3,3.3);

... process result set ...

$dbh->disconnect;

Accessing Fields in the Result Set

The fetchrow_array(), bind_columns() and fetch() functions are useful for processing result sets. fetchrow_array() returns an array of values. bind_columns() associates variables with columns which are set when fetch() is called.

Here's an example using fetchrow_array().

#!/usr/bin/env perl

use DBI;

my $dbh=DBI->connect("DBI:SQLRelay:host=sqlrserver;port=9000;socket=/tmp/example.socket;tries=0;retrytime=1;debug=0","exampleuser","examplepassword");

my $sth=$dbh->prepare("select * from user_tables");

$sth->execute();

while (@data=$sth->fetchrow_array()) {
        
        foreach $col (@data) {
                print "\"$col\",";
        }
        print "\n";
}

$dbh->disconnect;

Here's an example using bind_columns() and fetch(). Note that the first bind_columns() parameter must be "undef".

#!/usr/bin/env perl

use DBI;

my $dbh=DBI->connect("DBI:SQLRelay:host=sqlrserver;port=9000;socket=/tmp/example.socket;tries=0;retrytime=1;debug=0","exampleuser","examplepassword");

my $sth=$dbh->prepare("select * from my_table");

$sth->execute();
$sth->bind_columns(undef,\$col1,\$col2,\$col3,\$col4);

while ($sth->fetch()) {
        print "$col, $col2, $col3, $col4\n";
}

$dbh->disconnect;

Dealing With Large Result Sets

SQL Relay normally buffers the entire result set. This can speed things up at the cost of memory. With large enough result sets, it makes sense to buffer the result set in chunks instead of all at once.

Statements

It's possible to execute new queries while processing the result set of another query. You can select rows from a table in one query, then iterate through its result set, inserting rows into another table, using only 1 database connection for both operations.

For example:

#!/usr/bin/env perl

use DBI;

my $dbh=DBI->connect("DBI:SQLRelay:host=sqlrserver;port=9000;socket=/tmp/example.socket;tries=0;retrytime=1;debug=0","exampleuser","examplepassword");

my $sth=$dbh->prepare("select * from my_table where col1=:0 and col2=:1 and col3=:2");

$sth->execute(undef,"hello",1,1.1);

... process result set ...

$sth->execute(undef,"hi",2,2.2);

... process result set ...

$sth->execute(undef,"goodbye",3,3.3);

... process result set ...

$dbh->disconnect;

Getting Column Information

After executing a query, the column count is stored in the NUMBER_OF_FIELDS statement property and column names are stored in the NAME statement property. They are accessible as follows:

#!/usr/bin/env perl

use DBI;

my $dbh=DBI->connect("DBI:SQLRelay:host=sqlrserver;port=9000;socket=/tmp/example.socket;tries=0;retrytime=1;debug=0","exampleuser","examplepassword");

my $sth=$dbh->prepare("select * from my_table");

$sth->execute();

for ($i=1; $i<=$sth->{NUM_OF_FIELDS}; $i++) {
       print "Column $i: $sth->{NAME}->[$i-1]\n";
}

$dbh->disconnect;

Stored Procedures

Many databases support stored procedures. Stored procedures are sets of queries and procedural code that are executed inside of the database itself. For example, a stored procedure may select rows from one table, iterate through the result set and, based on the values in each row, insert, update or delete rows in other tables. A client program could do this as well, but a stored procedure is generally more efficient because queries and result sets don't have to be sent back and forth between the client and database. Also, stored procedures are generally stored in the database in a compiled state, while queries may have to be re-parsed and re-compiled each time they are sent.

While many databases support stored procedures. The syntax for creating and executing stored procedures varies greatly between databases.

Stored procedures typically take input paramters from client programs through input bind variables and return values back to client programs either through bind variables or result sets. Stored procedures can be broken down into several categories, based on the values that they return. Some stored procedures don't return any values, some return a single value, some return multiple values and some return entire result sets.

No Values

Some stored procedures don't return any values. Below are examples, illustrating how to create, execute and drop this kind of stored procedure for each database that SQL Relay supports.

Oracle

To create the stored procedure, run a query like the following.

create procedure exampleproc(in1 in number, in2 in number, in3 in varchar2) is
begin
        insert into mytable values (in1,in2,in3);
end;

To execute the stored procedure from an SQL Relay program, use code like the following.

my $sth->$dbh->prepare("begin exampleproc(:in1,:in2,:in3); end;");
$sth->bind_param("in1",1);
$sth->bind_param("in2",1.1,2,1);
$sth->bind_param("in3","hello");
$sth->execute();

To drop the stored procedure, run a query like the following.

drop procedure exampleproc

Sybase and Microsoft SQL Server

To create the stored procedure, run a query like the following.

create procedure exampleproc @in1 int, @in2 float, @in3 varchar(20) as
        insert into mytable values (@in1,@in2,@in3)

To execute the stored procedure from an SQL Relay program, use code like the following.

my $sth->$dbh->prepare("exec exampleproc");
$sth->bind_param("in1",1);
$sth->bind_param("in2",1.1,2,1);
$sth->bind_param("in3","hello");
$sth->execute();

To drop the stored procedure, run a query like the following.

drop procedure exampleproc

Firebird

To create the stored procedure, run a query like the following.

create procedure exampleproc(in1 integer, in2 float, in3 varchar(20)) as
begin
        insert into mytable values (in1,in2,in3);
        suspend;
end;

To execute the stored procedure from an SQL Relay program, use code like the following.

my $sth=$dbh->prepare("execute procedure exampleproc ?, ?, ?");
$sth->bind_param("1",1);
$sth->bind_param("2",1.1,2,1);
$sth->bind_param("3","hello");
$sth->execute();

To drop the stored procedure, run a query like the following.

drop procedure exampleproc

DB2

To create the stored procedure, run a query like the following.

create procedure exampleproc(in in1 int, in in2 double, in in3 varchar(20)) language sql
begin
        insert into mytable values (in1,in2,in3);
end;

To execute the stored procedure from an SQL Relay program, use code like the following.

my $sth=$dbh->prepare("call exampleproc(?,?,?)");
$sth->bind_param("1",1);
$sth->bind_param("2",1.1,2,1);
$sth->bind_param("3","hello");
$sth->execute();

To drop the stored procedure, run a query like the following.

drop procedure exampleproc

Postgresql

To create the stored procedure, run a query like the following.

create function examplefunc(int,float,varchar(20)) returns void as '
begin
        insert into mytable values ($1,$2,$3);
        return;
end;' language plpgsql

To execute the stored procedure from an SQL Relay program, use code like the following.

my $sth=$dbh->prepare("select examplefunc($1,$2,$3)");
$sth->bind_param("1",1);
$sth->bind_param("2",1.1,2,1);
$sth->bind_param("3","hello");
$sth->execute();

To drop the stored procedure, run a query like the following.

drop function examplefunc(int,float,varchar(20))

MySQL/MariaDB

To create the stored procedure, run a query like the following.

create procedure exampleproc(in in1 int, in in2 float, in in3 varchar(20))
begin
        insert into mytable values (in1,in2,in3);
end;

To execute the stored procedure from an SQL Relay program, use code like the following.

my $sth=$dbh->prepare("select examplefunc(?,?,?)");
$sth->bind_param("1",1);
$sth->bind_param("2",1.1,4,2);
$sth->bind_param("3","hello");
$sth->execute();

To drop the stored procedure, run a query like the following.

drop procedure exampleproc

Single Values

Some stored procedures return single values. Below are examples, illustrating how to create, execute and drop this kind of stored procedure for each database that SQL Relay supports.

Oracle

In Oracle, stored procedures can return values through output parameters or as return values of the procedure itself.

Here is an example where the procedure itself returns a value. Note that Oracle calls these functions.

To create the stored procedure, run a query like the following.

create function exampleproc(in1 in number, in2 in number, in3 in varchar2) returns number is
begin
        return in1;
end;

To execute the stored procedure from an SQL Relay program, use code like the following.

my $sth=$dbh->prepare("select exampleproc(:in1,:in2,:in3) from dual");
$sth->bind_param("in1",1);
$sth->bind_param("in2",1.1,2,1);
$sth->bind_param("in3","hello");
$sth->execute();
my $result;
$sth->bind_columns(undef,\$result);
$sth->fetch();

To drop the stored procedure, run a query like the following.

drop procedure exampleproc

Here is an example where the value is returned through an output parameter.

To create the stored procedure, run a query like the following.

create procedure exampleproc(in1 in number, in2 in number, in3 in varchar2, out1 out number) as
begin
        out1:=in1;
end;

To execute the stored procedure from an SQL Relay program, use code like the following.

my $sth=$dbh->prepare("begin exampleproc(:in1,:in2,:in3,:out1); end;");
$sth->bind_param("in1",1);
$sth->bind_param("in2",1.1,2,1);
$sth->bind_param("in3","hello");
my $result;
$sth->bind_param_inout("out1",\$result,20);
$sth->execute();

To drop the stored procedure, run a query like the following.

drop procedure exampleproc

Sybase and Microsoft SQL Server

In Sybase and Microsoft SQL Server, stored procedures return values through output parameters rather than as return values of the procedure itself.

To create the stored procedure, run a query like the following.

create procedure exampleproc @in1 int, @in2 float, @in3 varchar(20), @out1 int output as
        select @out1=convert(varchar(20),@in1)

To execute the stored procedure from an SQL Relay program, use code like the following.

my $sth=$dth->prepare("exec exampleproc");
$sth->bind_param("in1",1);
$sth->bind_param("in2",1.1,2,1);
$sth->bind_param("in3","hello");
my $result;
$sth->bind_param_inout("out1",\$result,20);
$sth->execute();

To drop the stored procedure, run a query like the following.

drop procedure exampleproc

Firebird

To create the stored procedure, run a query like the following.

create procedure exampleproc(in1 integer, in2 float, in3 varchar(20)) returns (out1 integer) as
begin
        out1=in1;
        suspend;
end;

To execute the stored procedure from an SQL Relay program, use code like the following.

my $sth=$dth->prepare("select * from exampleproc(?,?,?)");
$sth->bind_param("1",1);
$sth->bind_param("2",1.1,2,1);
$sth->bind_param("3","hello");
$sth->execute();
my $result;
$sth->bind_columns(undef,\$result);
$sth->fetch();

Alternatively, you can run a query like the following and receive the result using an output bind variable. Note that in Firebird, input and output bind variable indices are distict from one another. The index of the output bind variable is 1 rather than 4, even though there were 3 input bind variables.

my $sth=$dbh->prepare("execute procedure exampleproc ?, ?, ?");
$sth->bind_param("1",1);
$sth->bind_param("2",1.1,2,1);
$sth->bind_param("3","hello");
my $result;
$sth->bind_param_inout("1",\$result,20);
$sth->execute();

To drop the stored procedure, run a query like the following.

drop procedure exampleproc

DB2

In DB2, stored procedures return values through output parameters rather than as return values of the procedure itself.

To create the stored procedure, run a query like the following.

create procedure exampleproc(in in1 int, in in2 double, in in3 varchar(20), out out1 int) language sql
begin
        set out1 = in1;
end

To execute the stored procedure from an SQL Relay program, use code like the following.

my $sth=$dbh->prepare("call exampleproc(?,?,?,?)");
$sth->bind_param("1",1);
$sth->bind_param("2",1.1,2,1);
$sth->bind_param("3","hello");
my $result;
$sth->bind_param_inout("4",\$result,25);
$sth->execute();

To drop the stored procedure, run a query like the following.

drop procedure exampleproc

Postgresql

To create the stored procedure, run a query like the following.

create function examplefunc(int,float,char(20)) returns int as '
declare
        in1 int;
        in2 float;
        in3 char(20);
begin
        in1:=$1;
        return;
end;
' language plpgsql

To execute the stored procedure from an SQL Relay program, use code like the following.

my $sth=$dbh->prepare("select * from examplefunc($1,$2,$3)");
$sth->bind_param("1",1);
$sth->bind_param("2",1.1,4,2);
$sth->bind_param("3","hello");
$sth->execute();
my $result;
$sth->bind_columns(undef,\$result);
$sth->fetch();

To drop the stored procedure, run a query like the following.

drop function examplefunc(int,float,char(20))

MySQL/MariaDB

A single value can be returned from a MySQL/MariaDB function.

To create the function, run a query like the following.

create function examplefunc(in in1 int, in in2 float, in in3 varchar(20)) returns int return in1;

To execute the function from an SQL Relay program, use code like the following.

my $sth=$dbh->prepare("select examplefunc(?,?,?)");
$sth->bind_param("1",1);
$sth->bind_param("2",1.1,4,2);
$sth->bind_param("3","hello");
$sth->execute();
my $out1;
$sth->bind_columns(undef,\$out1);
$sth->fetch();

To drop the function, run a query like the following.

drop procedure exampleproc

A single value can be returned in the result set of a MySQL/MariaDB procedure.

To create the procedure, run a query like the following.

create procedure exampleproc() begin select 1; end;

To execeute the procedure from an SQL Relay program, use code like the following.

my $sth=$dbh->prepare("select exampleproc()");
$sth->execute();
$sth->bind_columns(undef,\$out1);
$sth->fetch();

To drop the procedure, run a query like the following.

drop procedure exampleproc

A single value can be returned using the output variable of a MySQL/MariaDB procedure.

To create the procedure, run a query like the following.

create procedure exampleproc(out out1 int) begin select 1 into out1; end;

To execeute the procedure from an SQL Relay program, use code like the following.

my $sth=$dbh->prepare("select \@out1=0");
$sth->execute();
my $sth=$dbh->prepare("call exampleproc(\@out1)");
$sth->execute();
my $sth=$dbh->prepare("select \@out1");
$sth->execute();
$sth->bind_columns(undef,\$out1);
$sth->fetch();

To drop the procedure, run a query like the following.

drop procedure exampleproc

Multiple Values

Some stored procedures return multiple values. Below are examples, illustrating how to create, execute and drop this kind of stored procedure for each database that SQL Relay supports.

Oracle

In Oracle, stored procedures can return values through output parameters or as return values of the procedure itself. If a procedure needs to return multiple values, it can return one of them as the return value of the procedure itself, but the rest must be returned through output parameters.

To create the stored procedure, run a query like the following.

create procedure exampleproc(in1 in number, in2 in number, in3 in varchar2, out1 out number, out2 out number, out3 out varchar2) is
begin
        out1:=in1;
        out2:=in2;
        out3:=in3;
end;

To execute the stored procedure from an SQL Relay program, use code like the following.

my $sth=$dbh->prepare("begin exampleproc(:in1,:in2,:in3,:out1,:out2,:out3); end;");
$sth->bind_param("in1",1);
$sth->bind_param("in2",1.1,2,1);
$sth->bind_param("in3","hello");
my $out1;
my $out2;
my $out3;
$sth->bind_input_param("out1",\$out1,20);
$sth->bind_input_param("out2",\$out2,20);
$sth->bind_input_param("out3",\$out3,20);

To drop the stored procedure, run a query like the following.

drop procedure exampleproc

Sybase and Microsoft SQL Server

To create the stored procedure, run a query like the following.

create procedure exampleproc @in1 int, @in2 float, @in3 varchar(20), @out1 int output, @out2 int output, @out3 int output as
        select @out1=convert(varchar(20),@in1),
                @out2=convert(varchar(20),@in2),
                @out2=convert(varchar(20),@in2)

To execute the stored procedure from an SQL Relay program, use code like the following.

my $sth=$dth->prepare("exec exampleproc");
$sth->bind_param("in1",1);
$sth->bind_param("in2",1.1,2,1);
$sth->bind_param("in3","hello");
my $out1;
my $out2;
my $out3;
$sth->bind_param_inout("out1",\$out1,20);
$sth->bind_param_inout("out2",\$out2,20);
$sth->bind_param_inout("out3",\$out3,20);
$sth->execute();

To drop the stored procedure, run a query like the following.

drop procedure exampleproc

Firebird

To create the stored procedure, run a query like the following.

create procedure exampleproc(in1 integer, in2 float, in3 varchar(20)) returns (out1 integer, out2 float, out3 varchar(20)) as
begin
        out1=in1;
        out2=in2;
        out3=in3;
        suspend;
end;

To execute the stored procedure from an SQL Relay program, use code like the following.

my $sth=$dth->prepare("select * from exampleproc(?,?,?)");
$sth->bind_param("1",1);
$sth->bind_param("2",1.1,2,1);
$sth->bind_param("3","hello");
$sth->execute();
my $out1;
my $out2;
my $out3;
$sth->bind_columns(undef,\$out1,\$out1,\$out3);
$sth->fetch();

Alternatively, you can run a query like the following and receive the result using a output bind variables. Note that in Firebird, input and output bind variable indices are distict from one another. The index of the first output bind variable is 1 rather than 4, even though there were 3 input bind variables.

my $sth=$dbh->prepare("execute procedure exampleproc ?, ?, ?");
$sth->bind_param("1",1);
$sth->bind_param("2",1.1,2,1);
$sth->bind_param("3","hello");
my $out1;
my $out2;
my $out3;
$sth->bind_param_inout("1",\$out1,20);
$sth->bind_param_inout("2",\$out2,20);
$sth->bind_param_inout("3",\$out3,20);
$sth->execute();

To drop the stored procedure, run a query like the following.

drop procedure exampleproc

DB2

To create the stored procedure, run a query like the following.

create procedure exampleproc(in in1 int, in in2 double, in in3 varchar(20), out out1 int, out out2 double, out out3 varchar(20)) language sql
begin
        set out1 = in1;
        set out2 = in2;
        set out3 = in3;
end

To execute the stored procedure from an SQL Relay program, use code like the following.

my $sth=$dbh->prepare("call exampleproc(?,?,?,?,?,?)");
$sth->bind_param("1",1);
$sth->bind_param("2",1.1,2,1);
$sth->bind_param("3","hello");
my $out1;
my $out2;
my $out3;
$sth->bind_param_inout("4",\$out1,25);
$sth->bind_param_inout("5",\$out2,25);
$sth->bind_param_inout("6",\$out3,25);
$sth->execute();

To drop the stored procedure, run a query like the following.

drop procedure exampleproc

Postgresql

To create the stored procedure, run a query like the following.

create function examplefunc(int,float,char(20)) returns record as '
declare
        output record;
begin
        select $1,$2,$3 into output;
        return output;
end;
' language plpgsql

To execute the stored procedure from an SQL Relay program, use code like the following.

my $sth=$dbh->prepare("select * from examplefunc($1,$2,$3) as (col1 int, col2 float, col3 char(20))");
$sth->bind_param("1",1);
$sth->bind_param("2",1.1,4,2);
$sth->bind_param("3","hello");
$sth->execute();
my $out1;
my $out2;
my $out3;
$sth->bind_columns(undef,\$out1,\$out2,\$out3);
$sth->fetch();

To drop the stored procedure, run a query like the following.

drop function examplefunc(int,float,char(20))

MySQL/MariaDB

Here's how you can get multiple values from the result set of a MySQL/MariaDB procedure.

To create the stored procedure, run a query like the following.

create procedure exampleproc(in in1 int, in in2 float, in in3 varchar(20)) begin select in1, in2, in3; end;

To execute the stored procedure from an SQL Relay program, use code like the following.

my $sth=$dbh->prepare("call exampleproc(?,?,?)");
$sth->bind_param("1",1);
$sth->bind_param("2",1.1,4,2);
$sth->bind_param("3","hello");
$sth->execute();
my $out1;
my $out2;
my $out3;
$sth->bind_columns(undef,\$out1,\$out2,\$out3);
$sth->fetch();

To drop the stored procedure, run a query like the following.

drop procedure exampleproc

Here's how you can get multiple values from the output variables of a MySQL/MariaDB procedure.

To create the stored procedure, run a query like the following.

create procedure exampleproc(out out1 int, out out2 float, out out3 varchar(20)) begin select 1,1.1,'hello' into out1, out2, out3; end;

To execute the stored procedure from an SQL Relay program, use code like the following.

my $sth=$dbh->prepare("set \@out1=0, \@out2=0.0, \@out3='')");
$sth->execute();
$sth=$dbh->prepare("call exampleproc(\@out1,\@out2,\@out3)");
$sth->execute();
$sth=$dbh->prepare("select \@out1,\@out2,\@out3");
$sth->execute();
my $out1;
my $out2;
my $out3;
$sth->bind_columns(undef,\$out1,\$out2,\$out3);
$sth->fetch();

To drop the stored procedure, run a query like the following.

drop procedure exampleproc

Result Sets

Some stored procedures return entire result sets. Below are examples, illustrating how to create, execute and drop this kind of stored procedure for each database that SQL Relay supports.

Oracle

Stored procedures in Oracle can return open cursors as return values or output parameters. A client-side cursor can be bound to this open cursor and rows can be fetched from it. However the SQL Relay driver for Perl DBI does not currently support output bind cursors.

Sybase and Microsoft SQL Server

To create the stored procedure, run a query like the following.

create procedure exampleproc as select * from exampletable

To exceute the stored procedure from an SQL Relay program, ue code like the following.

my $sth=$dbh->prepareQuery("exec exampleproc");
$sth->execute();
my $out1;
my $out2;
my $out3;
$sth->bind_columns(undef,\$out1,\$out2,\$out3);
while ($sth->fetch()) {
        print "$out1, $out2, $out3\n";
}

To drop the stored procedure, run a query like the following.

drop procedure exampleproc

Firebird

Stored procedures in Firebird can return a result set if a select query in the procedure selects values into the output parameters and then issues a suspend command, however SQL Relay doesn't currently support stored procedures that return result sets.

DB2

Stored procedures in DB2 can return a result set if the procedure is declared to return one, however SQL Relay doesn't currently support stored procedures that return result sets.

Postgresql

To create the stored procedure, run a query like the following.

create function examplefunc() returns setof record as '
        declare output record;
begin
        for output in select * from mytable loop
                return next output;
        end loop;
        return;
end;
' language plpgsql

To execute the stored procedure from an SQL Relay program, use code like the following.

my $sth=$dbh->prepare("select * from examplefunc() as (exampleint int, examplefloat float, examplechar char(40))");
$sth->execute();
my $col1;
my $col2;
my $col3;
$sth->bind_columns(undef,\$col1,\$col2,\$col3);
while ($sth->fetch()) {
        print "$col1, $col2, $col3\n";
}

To drop the stored procedure, run a query like the following.

drop function examplefunc

MySQL/MariaDB

The result sets of all select statements called within MySQL/MariaDB stored procedures (that aren't selected into variables) are returned from the procedure call. Though MySQL/MariaDB stored procedures can return multiple result sets, currently SQL Relay can only fetch the first result set.

To create the stored procedure which returns a result set, run a query like the following.

create procedure exampleproc() begin select * from mytable; end;

To execute the stored procedure from an SQL Relay program, use code like the following.

my $sth=$dbh->prepareQuery("call exampleproc(?,?,?)");
$sth->bind_param("1",1);
$sth->bind_param("2",1.1,4,2);
$sth->bind_param("3","hello");
$sth->execute();
my $out1;
my $out2;
my $out3;
$sth->bind_columns(undef,\$out1,\$out2,\$out3);
while ($sth->fetch()) {
        print "$out1, $out2, $out3\n";
}

To drop the stored procedure, run a query like the following.

drop procedure exampleproc

Getting the Last Insert ID

Databases with autoincrement or identity columns often provide functions which return the "last insert id"; the value of the autoincrement column that was generated during the insert into the database.

DBI provides the $dbh->last_insert_id() method to get this value.

When using the SQLite database, you can also get the last insert id by running the query:

select last insert rowid

Driver-Specific Attributes

Perl DBI allows drivers to define their own attributes for database handles and statements. These attributes can be set to control various parameters unique to the driver. SQL Relay implements several of these.

Database handle attributes defined by the SQL Relay driver:

• DBD::SQLRelay::Debug - set-only (1, 0 or file name), when set to 1, debug is enabled to standard output, when set to 0, debug is disabled, when set to a file name, debug is sent to that file.

Statement handle attributes defined by the SQL Relay driver: