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Queries
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.. contents:: Table of Contents

************
Query Basics
************

Regular Queries
===============

To submit a query, use the **query** function::

	$db->query('YOUR QUERY HERE');

The query() function returns a database result **object** when "read"
type queries are run which you can use to :doc:`show your
results <results>`. When "write" type queries are run it simply
returns TRUE or FALSE depending on success or failure. When retrieving
data you will typically assign the query to your own variable, like
this::

	$query = $db->query('YOUR QUERY HERE');

Simplified Queries
==================

The **simpleQuery** method is a simplified version of the
$db->query() method. It DOES
NOT return a database result set, nor does it set the query timer, or
compile bind data, or store your query for debugging. It simply lets you
submit a query. Most users will rarely use this function.

It returns whatever the database drivers' "execute" function returns.
That typically is TRUE/FALSE on success or failure for write type queries
such as INSERT, DELETE or UPDATE statements (which is what it really
should be used for) and a resource/object on success for queries with
fetchable results.

::

	if ($db->simpleQuery('YOUR QUERY'))
	{
		echo "Success!";
	}
	else
	{
		echo "Query failed!";
	}

.. note:: PostgreSQL's ``pg_exec()`` function (for example) always
	returns a resource on success even for write type queries.
	So keep that in mind if you're looking for a boolean value.

***************************************
Working with Database prefixes manually
***************************************

If you have configured a database prefix and would like to prepend it to
a table name for use in a native SQL query for example, then you can use
the following::

	$db->prefixTable('tablename'); // outputs prefix_tablename

If for any reason you would like to change the prefix programmatically
without needing to create a new connection you can use this method::

	$db->setPrefix('newprefix');
	$db->prefixTable('tablename'); // outputs newprefix_tablename

**********************
Protecting identifiers
**********************

In many databases it is advisable to protect table and field names - for
example with backticks in MySQL. **Query Builder queries are
automatically protected**, but if you need to manually protect an
identifier you can use::

	$db->protectIdentifiers('table_name');

.. important:: Although the Query Builder will try its best to properly
	quote any field and table names that you feed it. Note that it
	is NOT designed to work with arbitrary user input. DO NOT feed it
	with unsanitized user data.

This function will also add a table prefix to your table, assuming you
have a prefix specified in your database config file. To enable the
prefixing set TRUE (boolean) via the second parameter::

	$db->protectIdentifiers('table_name', TRUE);

****************
Escaping Queries
****************

It's a very good security practice to escape your data before submitting
it into your database. CodeIgniter has three methods that help you do
this:

#. **$db->escape()** This function determines the data type so
   that it can escape only string data. It also automatically adds
   single quotes around the data so you don't have to:
   ::

	$sql = "INSERT INTO table (title) VALUES(".$db->escape($title).")";

#. **$db->escapeString()** This function escapes the data passed to
   it, regardless of type. Most of the time you'll use the above
   function rather than this one. Use the function like this:
   ::

	$sql = "INSERT INTO table (title) VALUES('".$db->escapeString($title)."')";

#. **$db->escapeLikeString()** This method should be used when
   strings are to be used in LIKE conditions so that LIKE wildcards
   ('%', '\_') in the string are also properly escaped.

::

        $search = '20% raise';
        $sql = "SELECT id FROM table WHERE column LIKE '%" .
        $db->escapeLikeString($search)."%' ESCAPE '!'";

.. important:: The ``escapeLikeString()`` method uses '!' (exclamation mark)
	to escape special characters for *LIKE* conditions. Because this
	method escapes partial strings that you would wrap in quotes
	yourself, it cannot automatically add the ``ESCAPE '!'``
	condition for you, and so you'll have to manually do that.

**************
Query Bindings
**************

Bindings enable you to simplify your query syntax by letting the system
put the queries together for you. Consider the following example::

	$sql = "SELECT * FROM some_table WHERE id = ? AND status = ? AND author = ?";
	$db->query($sql, [3, 'live', 'Rick']);

The question marks in the query are automatically replaced with the
values in the array in the second parameter of the query function.

Binding also work with arrays, which will be transformed to IN sets::

	$sql = "SELECT * FROM some_table WHERE id IN ? AND status = ? AND author = ?";
	$db->query($sql, array(array(3, 6), 'live', 'Rick'));

The resulting query will be::

	SELECT * FROM some_table WHERE id IN (3,6) AND status = 'live' AND author = 'Rick'

The secondary benefit of using binds is that the values are
automatically escaped producing safer queries. 
You don't have to remember to manually escape data — the engine does it automatically for you.

Named Bindings
==============

Instead of using the question mark to mark the location of the bound values,
you can name the bindings, allowing the keys of the values passed in to match
placeholders in the query::

        $sql = "SELECT * FROM some_table WHERE id = :id: AND status = :status: AND author = :name:";
        $db->query($sql, [
                'id'     => 3,
                'status' => 'live',
                'name'   => 'Rick'
        ]);

.. note:: Each name in the query MUST be surrounded by colons.

***************
Handling Errors
***************

**$db->error();**

If you need to get the last error that has occurred, the error() method
will return an array containing its code and message. Here's a quick
example::

	if ( ! $db->simpleQuery('SELECT `example_field` FROM `example_table`'))
	{
		$error = $db->error(); // Has keys 'code' and 'message'
	}

****************
Prepared Queries
****************

Most database engines support some form of prepared statements, that allow you to prepare a query once, and then run
that query multiple times with new sets of data. This eliminates the possibility of SQL injection since the data is
passed to the database in a different format than the query itself. When you need to run the same query multiple times
it can be quite a bit faster, too. However, to use it for every query can have major performance hits, since you're calling
out to the database twice as often. Since the Query Builder and Database connections already handle escaping the data
for you, the safety aspect is already taken care of for you. There will be times, though, when you need to ability
to optimize the query by running a prepared statement, or prepared query.

Preparing the Query
===================

This can be easily done with the ``prepare()`` method. This takes a single parameter, which is a Closure that returns
a query object. Query objects are automatically generated by any of the "final" type queries, including **insert**,
**update**, **delete**, **replace**, and **get**. This is handled the easiest by using the Query Builder to
run a query. The query is not actually run, and the values don't matter since they're never applied, acting instead
as placeholders. This returns a PreparedQuery object::

    $pQuery = $db->prepare(function($db)
    {
        return $db->table('user')
                   ->insert([
                        'name'    => 'x',
                        'email'   => 'y',
                        'country' => 'US'
                   ]);
    });

If you don't want to use the Query Builder you can create the Query object manually using question marks for
value placeholders::

    $pQuery = $db->prepare(function($db)
    {
        $sql = "INSERT INTO user (name, email, country) VALUES (?, ?, ?)";

        return new Query($db)->setQuery($sql);
    });

If the database requires an array of options passed to it during the prepare statement phase you can pass that
array through in the second parameter::

    $pQuery = $db->prepare(function($db)
    {
        $sql = "INSERT INTO user (name, email, country) VALUES (?, ?, ?)";

        return new Query($db)->setQuery($sql);
    }, $options);

Executing the Query
===================

Once you have a prepared query you can use the ``execute()`` method to actually run the query. You can pass in as
many variables as you need in the query parameters. The number of parameters you pass must match the number of
placeholders in the query. They must also be passed in the same order as the placeholders appear in the original
query::

    // Prepare the Query
    $pQuery = $db->prepare(function($db)
    {
        return $db->table('user')
                   ->insert([
                        'name'    => 'x',
                        'email'   => 'y',
                        'country' => 'US'
                   ]);
    });

    // Collect the Data
    $name    = 'John Doe';
    $email   = 'j.doe@example.com';
    $country = 'US';

    // Run the Query
    $results = $pQuery->execute($name, $email, $country);

This returns a standard :doc:`result set </database/results>`.

Other Methods
=============

In addition to these two primary methods, the prepared query object also has the following methods:

**close()**

While PHP does a pretty good job of closing all open statements with the database it's always a good idea to
close out the prepared statement when you're done with it::

    $pQuery->close();

**getQueryString()**

This returns the prepared query as a string.

**hasError()**

Returns boolean true/false if the last execute() call created any errors.

**getErrorCode()**
**getErrorMessage()**

If any errors were encountered these methods can be used to retrieve the error code and string.

**************************
Working with Query Objects
**************************

Internally, all queries are processed and stored as instances of
\CodeIgniter\Database\Query. This class is responsible for binding
the parameters, otherwise preparing the query, and storing performance
data about its query.

**getLastQuery()**

When you just need to retrieve the last Query object, use the
getLastQuery() method::

	$query = $db->getLastQuery();
	echo (string)$query;

The Query Class
===============

Each query object stores several pieces of information about the query itself.
This is used, in part, by the Timeline feature, but is available for your use
as well.

**getQuery()**

Returns the final query after all processing has happened. This is the exact
query that was sent to the database::

	$sql = $query->getQuery();

This same value can be retrieved by casting the Query object to a string::

	$sql = (string)$query;

**getOriginalQuery()**

Returns the raw SQL that was passed into the object. This will not have any
binds in it, or prefixes swapped out, etc::

	$sql = $query->getOriginalQuery();

**hasError()**

If an error was encountered during the execution of this query this method
will return true::

	if ($query->hasError())
	{
		echo 'Code: '. $query->getErrorCode();
		echo 'Error: '. $query->getErrorMessage();
	}

**isWriteType()**

Returns true if the query was determined to be a write-type query (i.e.
INSERT, UPDATE, DELETE, etc)::

	if ($query->isWriteType())
	{
		... do something
	}

**swapPrefix()**

Replaces one table prefix with another value in the final SQL. The first
parameter is the original prefix that you want replaced, and the second
parameter is the value you want it replaced with::

	$sql = $query->swapPrefix('ci3_', 'ci4_');

**getStartTime()**

Gets the time the query was executed in seconds with microseconds::

	$microtime = $query->getStartTime();

**getDuration()**

Returns a float with the duration of the query in seconds with microseconds::

	$microtime = $query->getDuration();
