I want to copy a single record from a table, modify some of the fields in the record and insert into the same table. The table has 90 columns.
Thought of using insert..select in one statement but there are 90 columns and i need to tell the column name in the select query. How can i do it in a better way in perldbi. Pls provide me an example.
Fetch and cache the column names for your table using the NAME statement attribute
my $sth = $dbh->prepare('SELECT * FROM my_table where 1=0');
$sth->execute;
my $cols = $sth->{NAME};
then use $cols to construct your insert...select using some replacement function to inject your modifications in the select.
my %mods_for_column = ( 'foo' => 'foo+10', 'bar' => 'trim(bar)' );
my $inscols = join(',', #$cols);
my $selcols = join(',',
map { exists($mods_for_column($_)) ? $mods_for_column($_) : $_ } #$cols
);
my $sql = "insert into my_table ($inscols) select $selcols from my_table where mumble...";
Related
I keep getting errors when attempting to use placeholders in my perl script for a Mysql routine.
Code :
use DBI;
my $driver = "mysql";
my $database = "database";
my $user = "exxxxxx";
my $password = "xxxxx";
my $dsn = "DBI:mysql:$database;mysql_local_infile=ON";
my $dbh = DBI->connect($dsn,$user,$password);
$dbh->do("SET \#tempc5 = (SELECT temp FROM day5 WHERE time = '00:00') ");
my $inter1 = i24;
$sth = $dbh->prepare( "SET \#sumadd5 = (SELECT ? FROM humid WHERE temp=\#tempc5) " );
$sth->bind_param( 1, $inter1 );
$sth->finish();
$dbh->disconnect();
This produces the following error:
Global symbol "$sth" requires explicit...
If I add a my $sth I get the following error:
Scalar found where operator expected...
Note that I am have no objection in trying this with $dbh->do("SET"
if possible.
The placeholders are not allowed for column names according to MySQL Manual for mysql_stmt_prepare() which is the function behind prepare.
The markers are legal only in certain places in SQL statements. For
example, they are permitted in the VALUES() list of an INSERT
statement (to specify column values for a row), or in a comparison
with a column in a WHERE clause to specify a comparison value.
However, they are not permitted for identifiers (such as table or
column names), or to specify both operands of a binary operator such
as the = equal sign. The latter restriction is necessary because it
would be impossible to determine the parameter type. In general,
parameters are legal only in Data Manipulation Language (DML)
statements, and not in Data Definition Language (DDL) statements.
If you think about it, it would not make sense to prepare a statement where you can change a column. Preparation of statement includes execution plan, but you can't plan execution of a statement where you don't know if given column has or doesn't have an index on it.
You can't use a placeholder there.
When you call prepare, all structural information about your tables is baked into the query, waiting for you to pass in data values to replace placeholders when you execute the query.
But you're trying to use a placeholder for a column name, which is part of the table's structure.
If you fix the Perl syntax to be:
my $inter1 = 'i24';
my $sth = $dbh->prepare( "SET \#sumadd5 = (SELECT ? FROM humid WHERE temp=\#tempc5) " );
$sth->execute($inter1);
it should run, but the ? will be treated as a data value rather than a column name (structural information). So you'll get the results of the SQL query
SET #sumadd5 = (SELECT 'i24' FROM humid WHERE temp=#tempc5)
instead of
SET #sumadd5 = (SELECT i24 FROM humid WHERE temp=#tempc5)
The subquery will return the literal value "i24" for each matching row rather than the value found in column i24.
You didn't quoted the vaule of $inter1. Change $inter1 = i24; to $inter1 = 'i24';. Just edited in your code, this will not give you syntax error.
use warnings;
use strict;
use DBI;
my $driver = "mysql";
my $database = "database";
my $user = "exxxxxx";
my $password = "xxxxx";
my $dsn = "DBI:mysql:$database;mysql_local_infile=ON";
my $dbh = DBI->connect($dsn,$user,$password);
$dbh->do("SET \#tempc5 = (SELECT temp FROM day5 WHERE time = '00:00') ");
my $inter1 = 'i24';
my $sth = $dbh->prepare( "SET \#sumadd5 = (SELECT ? FROM humid WHERE temp=\#tempc5) " );
$sth->bind_param( 1, $inter1 );
$sth->finish();
$dbh->disconnect();
sub insert {
my ($self) = #_;
my $data = $self->{data};
my $keys = join( ', ', keys $data);
my $values = join( ', ', map qq('$_'), values $data);
my $sql = "INSERT INTO tbl ($keys) VALUES ($values);";
my $sth = $self->{dbh}->prepare($sql);
$sth->execute();
}
I have a method that inserts the contents of a hash ref into a one table sqlite database. I was wondering if there was a simple way to add a column to the table if the hash key is not already a column. Obviously if one of the keys is not a column name, the insert will fail. Can I capitalize on that failure, add the missing columns, and redo the insert. Or would I have to check all columns against all the keys each time I want to insert into the database? (All keys have TEXT values)
Alter your table based on the info you get using PRAGMA
my $inf_query = $db->prepare("PRAGMA table_info('tbl')");
$inf_query->execute();
my #inf = map { $_->[1] } #{$inf_query->fetchall_arrayref()};
#inf will be an array containing the columns present in the table, and you can use that info to construct your ALTER query.
Edited to return an array you can use to grep ;)
When I fetch the data this way is it possible then to access the column names and the column types or do I need an explicit prepare to reach this?
use DBI;
my $dbh = DBI->connect( ... );
my $select = "...";
my #arguments = ( ... );
my $ref = $dbh->selectall_arrayref( $select, {}, #arguments, );
Update:
With prepare I would do it this way:
my $sth = $dbh->prepare( $select );
$sth->execute( #arguments );
my $col_names = $sth->{NAME};
my $col_types = $sth->{TYPE};
my $ref = $sth->fetchall_arrayref;
unshift #$ref, $col_names;
The best solution is to use prepare to get a statement handle, as you describe in the second part of your question. If you use selectall_hashref or selectall_arrayref, you don't get a statement handle, and have to query the column type information yourself via $dbh->column_info (docs):
my $sth = $dbh->column_info('','',$table,$column); # or $column='' for all
my $info = $sth->fetchall_arrayref({});
use Data::Dumper; print Dumper($info);
(specifically, the COLUMN_NAME and TYPE_NAME attributes).
However, this introduces a race condition if the table changes schema between the two queries.
Also, you may use selectall_arrayref with the Slice parameter to fetch all the columns into a hash ref, it needs no prepared statement and will return an array ref of the result set rows, with each rows columns the key's to a hash and the values are the column values. ie:
my $result = $dbh->selectall_arrayref( qq{
SELECT * FROM table WHERE condition = value
}, { Slice => {} }) or die "Error: ".$dbh->errstr;
$result = [
[0] = { column1 => 'column1Value', column2 => 'column2Value', etc...},
[1] = { column1 => 'column1Value', column2 => 'column2Value', etc...},
];
Making it easy to iterate over results.. ie:
for my $row ( #$results ){
print "$row->{column1Value}, $row->{column2Value}\n";
}
You can also specify which columns to extract but it's pretty useless due to the fact it's more efficient to do that in your SQL query syntax.
{ Slice => { column1Name => 1, column2Name => 1 } }
That would only return the values for column1Name and column2Name just like saying in your SQL:
SELECT column1Name, column2Name FROM table...
The access to read from the db has been given to me via mssql stored procedures that return result sets rather than tables or views. But I want to be able to read the data using ORM.
I tried to use DBIx::Class::ResultSource::View to do the procedure call (e.g. EXEC my_stored_proc ?) as a custom query but this didn't work because it tried to convert the procedure call into a select statement.
Does anyone have another suggestion?
No, there is no reasonable way to execute a stored procedure in the context of DBIx::Class.
As far as I can tell, the closest thing to a workaround is "using the ORM" to get a database handle, which is weak soup:
my #results = $schema->storage->dbh_do(sub{
my ($storage, $dbh, #args) = #_;
my $sth = $dbh->prepare('call storedProcNameFooBar()');
my #data;
$sth->execute();
while( my $row = $sth->fetchrow_hashref){
push #data, $row;
}
return #data;
},());
[ see details at
http://metacpan.org/pod/DBIx::Class::Storage::DBI#dbh_do ]
...as you get none of the benefits of an ORM for your trouble.
You can use register_source
package My::Schema::User;
use base qw/DBIx::Class/;
# ->load_components, ->table, ->add_columns, etc.
# Make a new ResultSource based on the User class
my $source = __PACKAGE__->result_source_instance();
my $new_source = $source->new( $source );
$new_source->source_name( 'UserFriendsComplex' );
# Hand in your query as a scalar reference
# It will be added as a sub-select after FROM,
# so pay attention to the surrounding brackets!
$new_source->name( \<<SQL );
( SELECT u.* FROM user u
INNER JOIN user_friends f ON u.id = f.user_id
WHERE f.friend_user_id = ?
UNION
SELECT u.* FROM user u
INNER JOIN user_friends f ON u.id = f.friend_user_id
WHERE f.user_id = ? )
SQL
# Finally, register your new ResultSource with your Schema
My::Schema->register_source( 'UserFriendsComplex' => $new_source );
To call with parameters do the following
my $friends = [ $schema->resultset( 'UserFriendsComplex' )->search( {
+},
{
bind => [ 12345, 12345 ]
}
) ];
I'm trying to use fetchAll on a query that has 2 variables. I can't figure out the syntax.
I can manage with only 1 variable:
$sql = "SELECT * FROM mytable WHERE field1 = ?";
$this->_db->fetchAll($sql,$value1); # that works
However I'm having some issues when query has multiple variables
$sql = "SELECT * FROM mytable WHERE field1 = ? AND field2 = ?";
$this->_db->fetchAll($sql,$value1,$value2); # doesn't work
$this->_db->fetchAll($sql,array("field1"=>$value1,"field2"=>$value2)); # doesn't work either
The reason why I want to use ? instead of placing the variables directly into the query is that I've learned that using ? allows for the query to be compiled generically by the db engine and improves performances.
There are two types of parameter, named parameters and positional parameters. You're mixing the two types and that won't work.
Named parameters match a placeholder by name. Names are started with the : symbol. The parameter names are not the same as the names of the columns you happen to use them for. You supply parameter values in an associative array, using the parameter name (not the column name) as the array keys. For example:
$sql = "SELECT * FROM mytable WHERE field1 = :param1 AND field2 = :param2";
$this->_db->fetchAll($sql,array("param1"=>$value1,"param2"=>$value2));
Positional parameters use the ? symbol for the placeholder. You supply parameter values using a simple (non-associative) array, and the order of values in the array must match the order of parameter placeholders in your query. For example:
$sql = "SELECT * FROM mytable WHERE field1 = ? AND field2 = ?";
$this->_db->fetchAll($sql,array($value1,$value2));
Most brands of SQL database natively support only one style or the other, but PDO attempts to support both, by rewriting the SQL if necessary before preparing the query. Since Zend_Db is modeled after PDO, Zend_Db also supports both parameter styles.
This question is a bit old, but I thought I'd just add to it for reference sake.
I would recommend starting to use Zend_Db_Select with Zend_Db. I've been doing a lot with Zend_Db lately. More from Zend_Db_Select reference guide.
Lets assume you have a Zend_Db adapter: $this->_db
# this will get the Zend_Db_Select object
$select = $this->_db->select();
# now you build up your query with Zend_Db_Select functions
$select->from('mytable');
$select->where('field1 = ?', $field1);
$select->where('field2 = ?', $field2);
[...]
# echo to see the SQL (helps in debugging)
# SELECT * FROM mytable WHERE field1 = ? AND field2 = ? [...]
echo '<p>My SQL: ' . $select . '</p>';
# Execute the SQL / Fetch results
$results = $select->query()->fetchAll();
That's the basics from your given example, but the Zend Framework reference guide on the select object has a lot of good information on how to build even more complex queries with JOINS, UNIONS, GROUP BY, LIMIT, HAVING, etc.
If you wanted to use an alias name for a table or parameters, you use an associative array with the alias name being the index value:
# SELECT p.* FROM products AS p
$select->from('p' => 'products');
If you want to return only selected fields, you add an array of field names as a second parameter:
# SELECT model FROM products
$select->from(products, array(model));
Actually, the above could should produce fully qualified SQL as:
SELECT 'products'.model FROM 'products'
but I wrote the above for brevity and clarity in the example.
One thing I just came across is using AND and OR in the WHERE condition.
# WHERE a = $a
$select->where('a = ?', $a);
# WHERE a = $a AND b = $b
$select->where('a = ?', $a);
$select->where('b = ?', $b);
# WHERE a = $a OR b = $b
$select->where('a = ?', $a);
$select->orWhere('b = ?', $b);
# WHERE a = $a AND b = $b
$select->orWhere('a = ?', $a);
$select->where('b = ?', $b);
Notice, that whatever the following "where" function you use, will combine with the previous statement as that operand. Ok, that sounded confusing.
If the second "where" is an "OR" it will be an "OR" conditional. If the second "where" is a "AND" the statement will be "AND".
In other words, the first WHERE function is ignored in terms of what condition it will use.
In fact, I just asked a question on Stack Overflow yesterday regarding doing a complex WHERE using select.
Hope that helps!
Cheers!
Try this:
$sql = "SELECT * FROM mytable WHERE field1 = ? AND field2 = ?";
$statement = $this->_db->query($sql,array("field1"=>$value1,"field2"=>$value2));
$data = $statement->fetchAll();
$this->_db must be an instance of Db adapter.
Heres the actual Zend way to code for this.
$sql = "SELECT * FROM mytable WHERE field1 = :param1 AND field2 = :param2";
$this->_db->fetchAll($sql,array("param1"=>$value1,"param2"=>$value2));
$where = $this->_db->select()
->from('mytable')
->where('field1 = ?',$value1)
->where('field2 = ?',$value2);
$rowSet = $this->_db->fetchAll($where);
This works great for me