summaryrefslogtreecommitdiffstats
path: root/user_guide_src/source/database/query_builder.rst
blob: 3203ff103748da29462b72a94550f7ec0acd50ed (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
###################
Query Builder Class
###################

CodeIgniter gives you access to a Query Builder class. This pattern 
allows information to be retrieved, inserted, and updated in your 
database with minimal scripting. In some cases only one or two lines
of code are necessary to perform a database action.
CodeIgniter does not require that each database table be its own class
file. It instead provides a more simplified interface.

Beyond simplicity, a major benefit to using the Query Builder features
is that it allows you to create database independent applications, since
the query syntax is generated by each database adapter. It also allows
for safer queries, since the values are escaped automatically by the
system.

.. note:: If you intend to write your own queries you can disable this
	class in your database config file, allowing the core database library
	and adapter to utilize fewer resources.

.. contents::
    :local:
    :depth: 1

**************
Selecting Data
**************

The following functions allow you to build SQL **SELECT** statements.

$this->db->get()
----------------

Runs the selection query and returns the result. Can be used by itself
to retrieve all records from a table::

	$query = $this->db->get('mytable');  // Produces: SELECT * FROM mytable

The second and third parameters enable you to set a limit and offset
clause::

	$query = $this->db->get('mytable', 10, 20);
	// Produces: SELECT * FROM mytable LIMIT 20, 10 
        // (in MySQL. Other databases have slightly different syntax)

You'll notice that the above function is assigned to a variable named
$query, which can be used to show the results::

	$query = $this->db->get('mytable');

	foreach ($query->result() as $row)
	{
		echo $row->title;
	}

Please visit the :doc:`result functions <results>` page for a full
discussion regarding result generation.

:returns:	DB_Result for a successful "read", 
                TRUE for a successful "write", FALSE if an error

$this->db->get_compiled_select()
--------------------------------

Compiles the selection query just like **$this->db->get()** but does not *run*
the query. This method simply returns the SQL query as a string.

Example::

	$sql = $this->db->get_compiled_select('mytable');
	echo $sql;

	// Produces string: SELECT * FROM mytable

The second parameter enables you to set whether or not the query builder query
will be reset (by default it will be reset, just like when using `$this->db->get()`)::

	echo $this->db->limit(10,20)->get_compiled_select('mytable', FALSE);
	// Produces string: SELECT * FROM mytable LIMIT 20, 10
	// (in MySQL. Other databases have slightly different syntax)

	echo $this->db->select('title, content, date')->get_compiled_select();

	// Produces string: SELECT title, content, date FROM mytable LIMIT 20, 10

The key thing to notice in the above example is that the second query did not
utilize **$this->db->from()** and did not pass a table name into the first
parameter. The reason for this outcome is because the query has not been
executed using **$this->db->get()** which resets values or reset directly
using **$this->db->reset_query()**.

:returns:	The SQL select string

$this->db->get_where()
----------------------

Identical to the above function except that it permits you to add a
"where" clause in the second parameter, instead of using the db->where()
function::

	$query = $this->db->get_where('mytable', array('id' => $id), $limit, $offset);

Please read the about the where function below for more information.

.. note:: get_where() was formerly known as getwhere(), which has been removed

:returns:	DB_Result for a successful "read", 
                TRUE for a successful "write", FALSE if an error

$this->db->select()
-------------------

Permits you to write the SELECT portion of your query::

	$this->db->select('title, content, date');
	$query = $this->db->get('mytable');  // Produces: SELECT title, content, date FROM mytable


.. note:: If you are selecting all (\*) from a table you do not need to
	use this function. When omitted, CodeIgniter assumes you wish to SELECT *

$this->db->select() accepts an optional second parameter. If you set it
to FALSE, CodeIgniter will not try to protect your field or table names
with backticks. This is useful if you need a compound select statement.

::

	$this->db->select('(SELECT SUM(payments.amount) FROM payments WHERE payments.invoice_id=4') AS amount_paid', FALSE);
	$query = $this->db->get('mytable');

:returns:	The query builder object

$this->db->select_max()
-----------------------

Writes a "SELECT MAX(field)" portion for your query. You can optionally
include a second parameter to rename the resulting field.

::

	$this->db->select_max('age');
	$query = $this->db->get('members');  // Produces: SELECT MAX(age) as age FROM members

	$this->db->select_max('age', 'member_age');
	$query = $this->db->get('members'); // Produces: SELECT MAX(age) as member_age FROM members


**$this->db->select_min()**

Writes a "SELECT MIN(field)" portion for your query. As with
select_max(), You can optionally include a second parameter to rename
the resulting field.

::

	$this->db->select_min('age');
	$query = $this->db->get('members'); // Produces: SELECT MIN(age) as age FROM members


**$this->db->select_avg()**

Writes a "SELECT AVG(field)" portion for your query. As with
select_max(), You can optionally include a second parameter to rename
the resulting field.

::

	$this->db->select_avg('age');
	$query = $this->db->get('members'); // Produces: SELECT AVG(age) as age FROM members


**$this->db->select_sum()**

Writes a "SELECT SUM(field)" portion for your query. As with
select_max(), You can optionally include a second parameter to rename
the resulting field.

::

	$this->db->select_sum('age');
	$query = $this->db->get('members'); // Produces: SELECT SUM(age) as age FROM members

:returns:	The query builder object


$this->db->from()
-----------------

Permits you to write the FROM portion of your query::

	$this->db->select('title, content, date');
	$this->db->from('mytable');
	$query = $this->db->get();  // Produces: SELECT title, content, date FROM mytable

.. note:: As shown earlier, the FROM portion of your query can be specified
	in the $this->db->get() function, so use whichever method you prefer.

:returns:	The query builder object

$this->db->join()
-----------------

Permits you to write the JOIN portion of your query::

	$this->db->select('*');
	$this->db->from('blogs');
	$this->db->join('comments', 'comments.id = blogs.id');
	$query = $this->db->get();

	// Produces:
	// SELECT * FROM blogs JOIN comments ON comments.id = blogs.id

Multiple function calls can be made if you need several joins in one
query.

If you need a specific type of JOIN you can specify it via the third
parameter of the function. Options are: left, right, outer, inner, left
outer, and right outer.

::

	$this->db->join('comments', 'comments.id = blogs.id', 'left');
	// Produces: LEFT JOIN comments ON comments.id = blogs.id

:returns:	The query builder object

*************************
Looking for Specific Data
*************************

$this->db->where()
------------------

This function enables you to set **WHERE** clauses using one of four
methods:

.. note:: All values passed to this function are escaped automatically,
	producing safer queries.

#. **Simple key/value method:**

	::

		$this->db->where('name', $name); // Produces: WHERE name = 'Joe'

	Notice that the equal sign is added for you.

	If you use multiple function calls they will be chained together with
	AND between them:

	::

		$this->db->where('name', $name);
		$this->db->where('title', $title);
		$this->db->where('status', $status);
		// WHERE name = 'Joe' AND title = 'boss' AND status = 'active'

#. **Custom key/value method:**
	You can include an operator in the first parameter in order to
	control the comparison:

	::

		$this->db->where('name !=', $name);
		$this->db->where('id <', $id); // Produces: WHERE name != 'Joe' AND id < 45

#. **Associative array method:**

	::

		$array = array('name' => $name, 'title' => $title, 'status' => $status);
		$this->db->where($array);
		// Produces: WHERE name = 'Joe' AND title = 'boss' AND status = 'active'

	You can include your own operators using this method as well:

	::

		$array = array('name !=' => $name, 'id <' => $id, 'date >' => $date);
		$this->db->where($array);

#. **Custom string:**
	You can write your own clauses manually::

		$where = "name='Joe' AND status='boss' OR status='active'";
		$this->db->where($where);


$this->db->where() accepts an optional third parameter. If you set it to
FALSE, CodeIgniter will not try to protect your field or table names
with backticks.

::

	$this->db->where('MATCH (field) AGAINST ("value")', NULL, FALSE);

**$this->db->or_where()**

This function is identical to the one above, except that multiple
instances are joined by OR::

	$this->db->where('name !=', $name);
	$this->db->or_where('id >', $id);  // Produces: WHERE name != 'Joe' OR id > 50

.. note:: or_where() was formerly known as orwhere(), which has been
	removed.

:returns:	The query builder object

$this->db->where_in()
---------------------

Generates a WHERE field IN ('item', 'item') SQL query joined with AND if
appropriate

::

	$names = array('Frank', 'Todd', 'James');
	$this->db->where_in('username', $names);
	// Produces: WHERE username IN ('Frank', 'Todd', 'James')


**$this->db->or_where_in()**

Generates a WHERE field IN ('item', 'item') SQL query joined with OR if
appropriate

::

	$names = array('Frank', 'Todd', 'James');
	$this->db->or_where_in('username', $names);
	// Produces: OR username IN ('Frank', 'Todd', 'James')

:returns:	The query builder object

$this->db->where_not_in()
-------------------------

Generates a WHERE field NOT IN ('item', 'item') SQL query joined with
AND if appropriate

::

	$names = array('Frank', 'Todd', 'James');
	$this->db->where_not_in('username', $names);
	// Produces: WHERE username NOT IN ('Frank', 'Todd', 'James')


**$this->db->or_where_not_in()**

Generates a WHERE field NOT IN ('item', 'item') SQL query joined with OR
if appropriate

::

	$names = array('Frank', 'Todd', 'James');
	$this->db->or_where_not_in('username', $names);
	// Produces: OR username NOT IN ('Frank', 'Todd', 'James')

:returns:	The query builder object


************************
Looking for Similar Data
************************

$this->db->like()
-----------------

This method enables you to generate **LIKE** clauses, useful for doing
searches.

.. note:: All values passed to this method are escaped automatically.

#. **Simple key/value method:**

	::

		$this->db->like('title', 'match');
		// Produces: WHERE `title` LIKE '%match%' ESCAPE '!'

	If you use multiple method calls they will be chained together with
	AND between them::

		$this->db->like('title', 'match');
		$this->db->like('body', 'match');
		// WHERE `title` LIKE '%match%' ESCAPE '!' AND  `body` LIKE '%match% ESCAPE '!'

	If you want to control where the wildcard (%) is placed, you can use
	an optional third argument. Your options are 'before', 'after' and
	'both' (which is the default).

	::

		$this->db->like('title', 'match', 'before');	// Produces: WHERE `title` LIKE '%match' ESCAPE '!'
		$this->db->like('title', 'match', 'after');	// Produces: WHERE `title` LIKE 'match%' ESCAPE '!'
		$this->db->like('title', 'match', 'both');	// Produces: WHERE `title` LIKE '%match%' ESCAPE '!'

#. **Associative array method:**

	::

		$array = array('title' => $match, 'page1' => $match, 'page2' => $match);
		$this->db->like($array);
		// WHERE `title` LIKE '%match%' ESCAPE '!' AND  `page1` LIKE '%match%' ESCAPE '!' AND  `page2` LIKE '%match%' ESCAPE '!'


**$this->db->or_like()**

This method is identical to the one above, except that multiple
instances are joined by OR::

	$this->db->like('title', 'match'); $this->db->or_like('body', $match);
	// WHERE `title` LIKE '%match%' ESCAPE '!' OR  `body` LIKE '%match%' ESCAPE '!'

.. note:: ``or_like()`` was formerly known as ``orlike()``, which has been removed.

**$this->db->not_like()**

This method is identical to ``like()``, except that it generates
NOT LIKE statements::

	$this->db->not_like('title', 'match');	// WHERE `title` NOT LIKE '%match% ESCAPE '!'

**$this->db->or_not_like()**

This method is identical to ``not_like()``, except that multiple
instances are joined by OR::

	$this->db->like('title', 'match');
	$this->db->or_not_like('body', 'match');
	// WHERE `title` LIKE '%match% OR  `body` NOT LIKE '%match%' ESCAPE '!'

:returns:	The query builder object

$this->db->group_by()
---------------------

Permits you to write the GROUP BY portion of your query::

	$this->db->group_by("title"); // Produces: GROUP BY title

You can also pass an array of multiple values as well::

	$this->db->group_by(array("title", "date"));  // Produces: GROUP BY title, date

.. note:: group_by() was formerly known as groupby(), which has been
	removed.

:returns:	The query builder object

$this->db->distinct()
---------------------

Adds the "DISTINCT" keyword to a query

::

	$this->db->distinct();
	$this->db->get('table'); // Produces: SELECT DISTINCT * FROM table

:returns:	The query builder object

$this->db->having()
-------------------

Permits you to write the HAVING portion of your query. There are 2
possible syntaxes, 1 argument or 2::

	$this->db->having('user_id = 45');  // Produces: HAVING user_id = 45
	$this->db->having('user_id',  45);  // Produces: HAVING user_id = 45

You can also pass an array of multiple values as well::

	$this->db->having(array('title =' => 'My Title', 'id <' => $id));
	// Produces: HAVING title = 'My Title', id < 45


If you are using a database that CodeIgniter escapes queries for, you
can prevent escaping content by passing an optional third argument, and
setting it to FALSE.

::

	$this->db->having('user_id',  45);  // Produces: HAVING `user_id` = 45 in some databases such as MySQL
	$this->db->having('user_id',  45, FALSE);  // Produces: HAVING user_id = 45


**$this->db->or_having()**

Identical to having(), only separates multiple clauses with "OR".

:returns:	The query builder object

****************
Ordering results
****************

$this->db->order_by()
---------------------

Lets you set an ORDER BY clause.

The first parameter contains the name of the column you would like to order by.

The second parameter lets you set the direction of the result.
Options are **ASC**, **DESC** AND **RANDOM**.

::

	$this->db->order_by('title', 'DESC');
	// Produces: ORDER BY `title` DESC

You can also pass your own string in the first parameter::

	$this->db->order_by('title DESC, name ASC');
	// Produces: ORDER BY `title` DESC, `name` ASC

Or multiple function calls can be made if you need multiple fields.

::

	$this->db->order_by('title', 'DESC');
	$this->db->order_by('name', 'ASC');
	// Produces: ORDER BY `title` DESC, `name` ASC

If you choose the **RANDOM** direction option, then the first parameters will
be ignored, unless you specify a numeric seed value.

::

	$this->db->order_by('title', 'RANDOM');
	// Produces: ORDER BY RAND()

	$this->db->order_by(42, 'RANDOM');
	// Produces: ORDER BY RAND(42)

.. note:: order_by() was formerly known as orderby(), which has been
	removed.

.. note:: Random ordering is not currently supported in Oracle and
	will default to ASC instead.

:returns:	The query builder object

****************************
Limiting or Counting Results
****************************

$this->db->limit()
------------------

Lets you limit the number of rows you would like returned by the query::

	$this->db->limit(10);  // Produces: LIMIT 10

The second parameter lets you set a result offset.

::

	$this->db->limit(10, 20);  // Produces: LIMIT 20, 10 (in MySQL.  Other databases have slightly different syntax)

:returns:	The query builder object

$this->db->count_all_results()
------------------------------

Permits you to determine the number of rows in a particular Active
Record query. Queries will accept Query Builder restrictors such as
where(), or_where(), like(), or_like(), etc. Example::

	echo $this->db->count_all_results('my_table');  // Produces an integer, like 25
	$this->db->like('title', 'match');
	$this->db->from('my_table');
	echo $this->db->count_all_results(); // Produces an integer, like 17

:returns:	Count of all the records returned by a query

$this->db->count_all()
----------------------

Permits you to determine the number of rows in a particular table.
Submit the table name in the first parameter. Example::

	echo $this->db->count_all('my_table');  // Produces an integer, like 25

:returns:	Count of all the records in the specified table

**************
Query grouping
**************

Query grouping allows you to create groups of WHERE clauses by enclosing them in parentheses. This will allow
you to create queries with complex WHERE clauses. Nested groups are supported. Example::

	$this->db->select('*')->from('my_table')
		->group_start()
			->where('a', 'a')
			->or_group_start()
				->where('b', 'b')
				->where('c', 'c')
			->group_end()
		->group_end()
		->where('d', 'd')
	->get();

	// Generates:
	// SELECT * FROM (`my_table`) WHERE ( `a` = 'a' OR ( `b` = 'b' AND `c` = 'c' ) ) AND `d` = 'd'

.. note:: groups need to be balanced, make sure every group_start() is matched by a group_end().

**$this->db->group_start()**

Starts a new group by adding an opening parenthesis to the WHERE clause of the query.

**$this->db->or_group_start()**

Starts a new group by adding an opening parenthesis to the WHERE clause of the query, prefixing it with 'OR'.

**$this->db->not_group_start()**

Starts a new group by adding an opening parenthesis to the WHERE clause of the query, prefixing it with 'NOT'.

**$this->db->or_not_group_start()**

Starts a new group by adding an opening parenthesis to the WHERE clause of the query, prefixing it with 'OR NOT'.

**$this->db->group_end()**

Ends the current group by adding an closing parenthesis to the WHERE clause of the query.

:returns:	The query builder object

**************
Inserting Data
**************

$this->db->insert()
-------------------

Generates an insert string based on the data you supply, and runs the
query. You can either pass an **array** or an **object** to the
function. Here is an example using an array::

	$data = array(
		'title' => 'My title',
		'name' => 'My Name',
		'date' => 'My date'
	);

	$this->db->insert('mytable', $data);
	// Produces: INSERT INTO mytable (title, name, date) VALUES ('My title', 'My name', 'My date')

The first parameter will contain the table name, the second is an
associative array of values.

Here is an example using an object::

	/*
	class Myclass {
		public $title = 'My Title';
		public $content = 'My Content';
		public $date = 'My Date';
	}
	*/

	$object = new Myclass;
	$this->db->insert('mytable', $object);
	// Produces: INSERT INTO mytable (title, content, date) VALUES ('My Title', 'My Content', 'My Date')

The first parameter will contain the table name, the second is an
object.

.. note:: All values are escaped automatically producing safer queries.

:returns:	DB_Query on success, FALSE on failure

$this->db->get_compiled_insert()
--------------------------------

Compiles the insertion query just like `$this->db->insert()`_ but does not
*run* the query. This method simply returns the SQL query as a string.

Example::

	$data = array(
		'title' => 'My title',
		'name'  => 'My Name',
		'date'  => 'My date'
	);

	$sql = $this->db->set($data)->get_compiled_insert('mytable');
	echo $sql;

	// Produces string: INSERT INTO mytable (title, name, date) VALUES ('My title', 'My name', 'My date')

The second parameter enables you to set whether or not the query builder query
will be reset (by default it will be--just like `$this->db->insert()`_)::

	echo $this->db->set('title', 'My Title')->get_compiled_insert('mytable', FALSE);

	// Produces string: INSERT INTO mytable (title) VALUES ('My Title')

	echo $this->db->set('content', 'My Content')->get_compiled_insert();

	// Produces string: INSERT INTO mytable (title, content) VALUES ('My Title', 'My Content')

The key thing to notice in the above example is that the second query did not
utlize `$this->db->from()` nor did it pass a table name into the first
parameter. The reason this worked is because the query has not been executed
using `$this->db->insert()` which resets values or reset directly using
`$this->db->reset_query()`.

.. note:: This method doesn't work for batched inserts.

:returns:	The SQL insert string

$this->db->insert_batch()
-------------------------

Generates an insert string based on the data you supply, and runs the
query. You can either pass an **array** or an **object** to the
function. Here is an example using an array::

	$data = array(
		array(
			'title' => 'My title',
			'name' => 'My Name',
			'date' => 'My date'
		),
		array(
			'title' => 'Another title',
			'name' => 'Another Name',
			'date' => 'Another date'
		)
	);

	$this->db->insert_batch('mytable', $data);
	// Produces: INSERT INTO mytable (title, name, date) VALUES ('My title', 'My name', 'My date'),  ('Another title', 'Another name', 'Another date')

The first parameter will contain the table name, the second is an
associative array of values.

.. note:: All values are escaped automatically producing safer queries.

:returns:	Count of the number of records inserted on success, FALSE on failure

*************
Updating Data
*************

$this->db->replace()
--------------------

This method executes a REPLACE statement, which is basically the SQL
standard for (optional) DELETE + INSERT, using *PRIMARY* and *UNIQUE*
keys as the determining factor.
In our case, it will save you from the need to implement complex
logics with different combinations of  ``select()``, ``update()``,
``delete()`` and ``insert()`` calls.

Example::

	$data = array(
		'title' => 'My title',
		'name'  => 'My Name',
		'date'  => 'My date'
	);

	$this->db->replace('table', $data);

	// Executes: REPLACE INTO mytable (title, name, date) VALUES ('My title', 'My name', 'My date')

In the above example, if we assume that the *title* field is our primary
key, then if a row containing 'My title' as the *title* value, that row
will be deleted with our new row data replacing it.

Usage of the ``set()`` method is also allowed and all fields are
automatically escaped, just like with ``insert()``.

:returns:	DB_query object on success, FALSE on failure

$this->db->set()
----------------

This function enables you to set values for inserts or updates.

**It can be used instead of passing a data array directly to the insert
or update functions:**

::

	$this->db->set('name', $name);
	$this->db->insert('mytable');  // Produces: INSERT INTO mytable (name) VALUES ('{$name}')

If you use multiple function called they will be assembled properly
based on whether you are doing an insert or an update::

	$this->db->set('name', $name);
	$this->db->set('title', $title);
	$this->db->set('status', $status);
	$this->db->insert('mytable');

**set()** will also accept an optional third parameter ($escape), that
will prevent data from being escaped if set to FALSE. To illustrate the
difference, here is set() used both with and without the escape
parameter.

::

	$this->db->set('field', 'field+1', FALSE);
	$this->db->insert('mytable'); // gives INSERT INTO mytable (field) VALUES (field+1)
	$this->db->set('field', 'field+1');
	$this->db->insert('mytable'); // gives INSERT INTO mytable (field) VALUES ('field+1')


You can also pass an associative array to this function::

	$array = array(
		'name' => $name,
		'title' => $title,
		'status' => $status
	);

	$this->db->set($array);
	$this->db->insert('mytable');

Or an object::

	/*
	class Myclass {
		public $title = 'My Title';
		public $content = 'My Content';
		public $date = 'My Date';
	}
	*/

	$object = new Myclass;
	$this->db->set($object);
	$this->db->insert('mytable');

:returns:	The query builder object

$this->db->update()
-------------------

Generates an update string and runs the query based on the data you
supply. You can pass an **array** or an **object** to the function. Here
is an example using an array::

	$data = array(
		'title' => $title,
		'name' => $name,
		'date' => $date
	);

	$this->db->where('id', $id);
	$this->db->update('mytable', $data);
	// Produces: // UPDATE mytable  // SET title = '{$title}', name = '{$name}', date = '{$date}' // WHERE id = $id

Or you can supply an object::

	/*
	class Myclass {
		public $title = 'My Title';
		public $content = 'My Content';
		public $date = 'My Date';
	}
	*/

	$object = new Myclass;
	$this->db->where('id', $id);
	$this->db->update('mytable', $object);
	// Produces: // UPDATE mytable  // SET title = '{$title}', name = '{$name}', date = '{$date}' // WHERE id = $id

.. note:: All values are escaped automatically producing safer queries.

You'll notice the use of the $this->db->where() function, enabling you
to set the WHERE clause. You can optionally pass this information
directly into the update function as a string::

	$this->db->update('mytable', $data, "id = 4");

Or as an array::

	$this->db->update('mytable', $data, array('id' => $id));

You may also use the $this->db->set() function described above when
performing updates.

:returns:	DB_query object on success, FALSE on failure

$this->db->update_batch()
-------------------------

Generates an update string based on the data you supply, and runs the query.
You can either pass an **array** or an **object** to the function.
Here is an example using an array::

	$data = array(
	   array(
	      'title' => 'My title' ,
	      'name' => 'My Name 2' ,
	      'date' => 'My date 2'
	   ),
	   array(
	      'title' => 'Another title' ,
	      'name' => 'Another Name 2' ,
	      'date' => 'Another date 2'
	   )
	);

	$this->db->update_batch('mytable', $data, 'title');

	// Produces:
	// UPDATE `mytable` SET `name` = CASE
	// WHEN `title` = 'My title' THEN 'My Name 2'
	// WHEN `title` = 'Another title' THEN 'Another Name 2'
	// ELSE `name` END,
	// `date` = CASE
	// WHEN `title` = 'My title' THEN 'My date 2'
	// WHEN `title` = 'Another title' THEN 'Another date 2'
	// ELSE `date` END
	// WHERE `title` IN ('My title','Another title')

The first parameter will contain the table name, the second is an associative
array of values, the third parameter is the where key.

.. note:: All values are escaped automatically producing safer queries.

.. note:: ``affected_rows()`` won't give you proper results with this method,
	due to the very nature of how it works. Instead, ``update_batch()``
	returns the number of rows affected.

:returns:	Count of the number of records affected on success, FALSE on failure

$this->db->get_compiled_update()
--------------------------------

This works exactly the same way as ``$this->db->get_compiled_insert()`` except
that it produces an UPDATE SQL string instead of an INSERT SQL string.

For more information view documentation for `$this->db->get_compiled_insert()`.

.. note:: This method doesn't work for batched updates.

:returns:	The SQL update string

*************
Deleting Data
*************

$this->db->delete()
-------------------

Generates a delete SQL string and runs the query.

::

	$this->db->delete('mytable', array('id' => $id));  // Produces: // DELETE FROM mytable  // WHERE id = $id

The first parameter is the table name, the second is the where clause.
You can also use the where() or or_where() functions instead of passing
the data to the second parameter of the function::

	$this->db->where('id', $id);
	$this->db->delete('mytable');

	// Produces:
	// DELETE FROM mytable
	// WHERE id = $id


An array of table names can be passed into delete() if you would like to
delete data from more than 1 table.

::

	$tables = array('table1', 'table2', 'table3');
	$this->db->where('id', '5');
	$this->db->delete($tables);


If you want to delete all data from a table, you can use the truncate()
function, or empty_table().

:returns:	DB_Query on success, FALSE on failure

$this->db->empty_table()
------------------------

Generates a delete SQL string and runs the
query.::

	  $this->db->empty_table('mytable'); // Produces: DELETE FROM mytable

:returns:	DB_Query on success, FALSE on failure


$this->db->truncate()
---------------------

Generates a truncate SQL string and runs the query.

::

	$this->db->from('mytable');
	$this->db->truncate();

	// or

	$this->db->truncate('mytable');

	// Produce:
	// TRUNCATE mytable

.. note:: If the TRUNCATE command isn't available, truncate() will
	execute as "DELETE FROM table".

:returns:	DB_Query on success, FALSE on failure

$this->db->get_compiled_delete()
--------------------------------

This works exactly the same way as ``$this->db->get_compiled_insert()`` except
that it produces a DELETE SQL string instead of an INSERT SQL string.

For more information view documentation for `$this->db->get_compiled_insert()`_.

:returns:	The SQL delete string



***************
Method Chaining
***************

Method chaining allows you to simplify your syntax by connecting
multiple functions. Consider this example::

	$query = $this->db->select('title')
			->where('id', $id)
			->limit(10, 20)
			->get('mytable');

.. _ar-caching:

*********************
Query Builder Caching
*********************

While not "true" caching, Query Builder enables you to save (or "cache")
certain parts of your queries for reuse at a later point in your
script's execution. Normally, when an Query Builder call is completed,
all stored information is reset for the next call. With caching, you can
prevent this reset, and reuse information easily.

Cached calls are cumulative. If you make 2 cached select() calls, and
then 2 uncached select() calls, this will result in 4 select() calls.
There are three Caching functions available:

**$this->db->start_cache()**

This function must be called to begin caching. All Query Builder queries
of the correct type (see below for supported queries) are stored for
later use.

**$this->db->stop_cache()**

This function can be called to stop caching.

**$this->db->flush_cache()**

This function deletes all items from the Query Builder cache.

:returns:	void

An example of caching
---------------------

Here's a usage example::

	$this->db->start_cache();
	$this->db->select('field1');
	$this->db->stop_cache();
	$this->db->get('tablename');
	//Generates: SELECT `field1` FROM (`tablename`)

	$this->db->select('field2');
	$this->db->get('tablename');
	//Generates:  SELECT `field1`, `field2` FROM (`tablename`)

	$this->db->flush_cache();
	$this->db->select('field2');
	$this->db->get('tablename');
	//Generates:  SELECT `field2` FROM (`tablename`)


.. note:: The following statements can be cached: select, from, join,
	where, like, group_by, having, order_by, set


***********************
Resetting Query Builder
***********************

$this->db->reset_query()
------------------------

Resetting Query Builder allows you to start fresh with your query without
executing it first using a method like $this->db->get() or $this->db->insert().
Just like the methods that execute a query, this will *not* reset items you've
cached using `Query Builder Caching`_.

This is useful in situations where you are using Query Builder to generate SQL
(ex. ``$this->db->get_compiled_select()``) but then choose to, for instance,
run the query::

	// Note that the second parameter of the get_compiled_select method is FALSE
	$sql = $this->db->select(array('field1','field2'))
					->where('field3',5)
					->get_compiled_select('mytable', FALSE);

	// ...
	// Do something crazy with the SQL code... like add it to a cron script for
	// later execution or something...
	// ...

	$data = $this->db->get()->result_array();

	// Would execute and return an array of results of the following query:
	// SELECT field1, field1 from mytable where field3 = 5;

.. note:: Double calls to ``get_compiled_select()`` while you're using the
	Query Builder Caching functionality and NOT resetting your queries
	will results in the cache being merged twice. That in turn will
	i.e. if you're caching a ``select()`` - select the same field twice.

:returns:	void