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1 | =head1 NAME |
2 | |
3 | DBIx::Class::Manual::SQLHackers::SELECT - DBIx::Class for SQL Hackers - SELECT |
4 | |
5 | =over |
6 | |
7 | =item L<Introduction|DBIx::Class::Manual::SQLHackers::Introduction> |
8 | |
9 | =item L<CREATE|DBIx::Class::Manual::SQLHackers::CREATE> |
10 | |
11 | =item L<INSERT|DBIx::Class::Manual::SQLHackers::INSERT> |
12 | |
13 | =item SELECT |
14 | |
15 | =item L<UPDATE|DBIx::Class::Manual::SQLHackers::UPDATE> |
16 | |
17 | =item L<DELETE|DBIx::Class::Manual::SQLHackers::DELETE> |
18 | |
19 | =item L<BEGIN, COMMIT|DBIx::Class::Manual::SQLHackers::Transactions> |
20 | |
21 | =back |
22 | |
23 | =head1 SELECTing data |
24 | |
25 | =head2 Fetching rows from a query |
26 | |
27 | SELECT id, username, dob, realname, password |
28 | FROM users; |
29 | |
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30 | In DBIx::Class queries (or more specifically query plans) are represented by ResultSet objects. These are created by calling B<search> on existing resultsets, while passing new search conditions or attributes. A query is not run against the database until data is explicitly requested. |
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31 | |
32 | You can either fetch all the data at once, or iterate over the results: |
33 | |
34 | =over |
35 | |
36 | =item 1. Create a Schema object representing the database you are working with: |
37 | |
38 | my $schema = MyDatabase::Schema->connect('dbi:SQLite:my.db'); |
39 | |
2f41b1a9 |
40 | =item 2. The B<resultset> method returns a ResultSet representing a query retrieving all columns of the given B<ResultSource> without conditions: |
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41 | |
42 | my $user_resultset = $schema->resultset('User'); |
43 | |
44 | =item 3. Fetch all users as Row objects using the B<all> method: |
45 | |
46 | my @users = $user_resultset->all(); |
47 | |
48 | =item 4. OR, fetch each user as a Row object using B<next>: |
49 | |
50 | while( my $user = $user_resultset->next()) { |
51 | } |
52 | |
53 | =back |
54 | |
55 | =head2 Fetching column values from a Row object |
56 | |
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57 | The Row object represents the results from a single data source in the query. The column values can be retrieved by using the accessor methods named after the column names. (By default that is; accessors can be changed in the L<Result Class|DBIx::Class::ResulSource> if needed.) |
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58 | |
59 | print $user->username; |
60 | |
abc32120 |
61 | See the L<DBIx::Class::Row> documentation for more things you can do |
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62 | with Row objects. |
63 | |
64 | =head2 Simple SELECT, one row via the primary key |
65 | |
66 | SELECT id, username, dob, realname, password |
67 | FROM users |
68 | WHERE id = 1; |
69 | |
70 | The B<find> method on a ResultSet is a shortcut to create a query based on the inputs, run the query, and return a single row as a Row object result. |
71 | |
72 | If passed a condition which matches multiple rows, a warning is given. |
73 | |
74 | =over |
75 | |
76 | =item 1. Create a Schema object representing the database you are working with: |
77 | |
78 | my $schema = MyDatabase::Schema->connect('dbi:SQLite:my.db'); |
79 | |
80 | =item 2. Call the B<find> method on the resultset for the L<ResultSource|DBIx::Class::ResultSource> you wish to fetch data from: |
81 | |
82 | my $fred_user = $schema->resultset('User')->find({ id => 1 }); |
83 | |
84 | =back |
85 | |
86 | B<$fred_user> is a now Row object. |
87 | |
88 | =head2 Simple SELECT, one row via a unique key |
89 | |
90 | SELECT id, username, dob, realname, password |
91 | FROM users |
92 | WHERE username = 'fredbloggs'; |
93 | |
abc32120 |
94 | B<find> also works well on unique constraints, for example the username of our user. Unique constraints can be defined on Result classes using B<add_unique_constraint> (See L<CREATE|DBIx::Class::Manual::SQLHackers::CREATE>). |
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95 | |
96 | =over |
97 | |
98 | =item 1. Create a Schema object representing the database you are working with: |
99 | |
100 | my $schema = MyDatabase::Schema->connect('dbi:SQLite:my.db'); |
101 | |
102 | =item 2. Call the B<find> method on the resultset for the L<ResultSource|DBIx::Class::ResultSource> you wish to fetch data from: |
103 | |
104 | my $fred_user = $schema->resultset('User')->find( |
105 | { username => 'fredbloggs' }, |
106 | { key => 'uniq_username' } |
107 | ); |
108 | |
109 | =back |
110 | |
111 | "uniq_username" is the name of a constraint defined on the User L<ResultSource|DBIx::Class::ResultSource> which specifies that the username column is unique across the table. The second argument to B<find> is a set of attributes, of which the "key" attribute defines which constraint to do a lookup on. |
112 | |
113 | =head2 Simple SELECT, with WHERE condition |
114 | |
115 | SELECT id, username, dob, realname, password |
116 | FROM users |
117 | WHERE dob = '1910-02-01'; |
118 | |
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119 | To select all users born on the date '1910-02-01', we can use the B<search> method to prepare a query. Search returns a new resultset with the search conditions stored in it; it does not run the query on the database. |
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120 | |
121 | =over |
122 | |
123 | =item 1. Create a Schema object representing the database you are working with: |
124 | |
125 | my $schema = MyDatabase::Schema->connect('dbi:SQLite:my.db'); |
126 | |
127 | =item 2. Call the B<search> method on the resultset for the L<ResultSource|DBIx::Class::ResultSource> you wish to fetch data from: |
128 | |
129 | my $dob_search = $schema->resultset('User')->search( |
130 | { dob => '1910-02-01' } |
131 | ); |
132 | |
133 | =back |
134 | |
abc32120 |
135 | To run the query, use the B<all> or B<next> methods shown at the beginning of this page. |
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136 | |
137 | =head2 SELECT with different WHERE conditions |
138 | |
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139 | Shown below are some common SQL WHERE conditions. The syntax for these is parsed by a module called L<SQL::Abstract>, which DBIx::Class uses. They can all be passed to the B<search> method as conditions. |
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140 | |
141 | SELECT id, username, dob, realname, password |
142 | FROM users |
143 | WHERE username LIKE 'fred%'; |
144 | |
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145 | =cut |
146 | |
147 | =pod |
148 | |
149 | my $name_search = $schema->resultset('User')->search( |
150 | { username => { '-like' => 'fred%' } } |
151 | ); |
152 | |
153 | =cut |
154 | |
155 | =pod |
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156 | |
157 | SELECT id, username, dob, realname, password |
158 | FROM users |
159 | WHERE dob BETWEEN '1910-01-01' AND '1910-12-31'; |
160 | |
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161 | =cut |
162 | |
163 | =pod |
164 | |
165 | my $year_dob_search = $schema->resultset('User')->search( |
166 | { dob => { '-between' => ['1910-01-01', '1910-12-31'] } } |
167 | ); |
168 | |
169 | =cut |
170 | |
171 | =pod |
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172 | |
173 | SELECT id, username, dob, realname, password |
174 | FROM users |
175 | WHERE dob IN ('1910-02-01', '1910-02-02'); |
176 | |
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177 | =cut |
178 | |
179 | =pod |
180 | |
181 | my $feb_dob_search = $schema->resultset('User')->search( |
182 | { dob => { '-in' => ['1910-02-01', '1910-02-02'] } } |
183 | ); |
184 | |
185 | =cut |
186 | |
187 | =pod |
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188 | |
189 | SELECT id, username, dob, realname, password |
190 | FROM users |
191 | WHERE dob >= 1911-01-01; |
192 | |
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193 | =cut |
194 | |
195 | =pod |
196 | |
197 | my $next_year_dob = $schema->resultset('User')->search( |
198 | { dob => { '>=', '1911-01-01' } } |
199 | ); |
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200 | |
201 | |
202 | =head2 SELECT with WHERE condition on JOINed table |
203 | |
204 | SELECT posts.id, created_date, title, post |
205 | FROM posts |
206 | JOIN users user ON user.id = posts.user_id |
207 | WHERE user.username = 'fredbloggs'; |
208 | |
209 | The second argument to B<search> is a hashref of attributes to apply to the query. One of them is B<join>, which is used to connect to other tables using the relationships defined in the Result classes. |
210 | |
211 | =over |
212 | |
213 | =item 1. Create a Schema object representing the database you are working with: |
214 | |
215 | my $schema = MyDatabase::Schema->connect('dbi:SQLite:my.db'); |
216 | |
217 | =item 2. Call the B<search> method on the resultset for the L<ResultSource|DBIx::Class::ResultSource> you wish to fetch data from: |
218 | |
219 | my $freds_posts = $schema->resultset('Post')->search( |
220 | { 'user.username' => 'fredbloggs' }, |
221 | { join => 'user' } |
222 | ); |
223 | |
224 | =back |
225 | |
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226 | Note that the string "user", used twice here, refers to the B<name> of the L<Relationship|DBIx::Class::Relationship> between the "Post" source and the "User" source. All dealings with related tables are referred to by relationship names, not table names. |
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227 | |
228 | To run the query, use the B<all> or B<next> methods show at the beginning of this page. |
229 | |
230 | =head2 SELECT with fewer columns |
231 | |
232 | SELECT id, title |
233 | FROM posts |
234 | |
235 | There's usually little reason to do this sort of query, as fetching all the data in a row doesn't cost any more time than fetching some of it. Unless of course your source is a View with calculations, or has huge blobs, or.. Okay, you might well want to do this occasionally. |
236 | |
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237 | =over |
238 | |
239 | =item 1. Create a Schema object representing the database you are working with: |
240 | |
241 | my $schema = MyDatabase::Schema->connect('dbi:SQLite:my.db'); |
242 | |
243 | =item 2. Call the B<search> method on the resultset for the L<ResultSource|DBIx::Class::ResultSource> you wish to fetch data from: |
244 | |
245 | my $post_titles = $schema->resultset('Post')->search( |
246 | { }, |
247 | { columns => [qw/id title/] } |
248 | ); |
249 | |
250 | =back |
251 | |
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252 | Note that accessors for other columns not fetched will return B<undef>, which is also the perl equivalent of the SQL C<NULL> value. To disambiguate between an C<undef> meaning "this column is set null" and "we never retrieved the value of this column" use L<DBIx::Class::Row::has_column_loaded|DBIx::Class::Row/has_column_loaded>. |
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253 | |
254 | |
255 | =head2 SELECT with aggregates |
256 | |
257 | SELECT COUNT(*) |
258 | FROM users; |
259 | |
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260 | Finding out how many users exist can be achieved with a built-in method, B<count>. |
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261 | |
262 | =over |
263 | |
264 | =item 1. Create a Schema object representing the database you are working with: |
265 | |
266 | my $schema = MyDatabase::Schema->connect('dbi:SQLite:my.db'); |
267 | |
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268 | =item 2. Call the B<count> method on the resultset for the L<ResultSource|DBIx::Class::ResultSource> you wish to fetch data from: |
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269 | |
270 | my $posts_count = $schema->resultset('Post')->count(); |
271 | |
272 | =back |
273 | |
274 | The result is not an object, just a number. |
275 | |
276 | SELECT SUM(amount) |
277 | FROM prices; |
278 | |
279 | A rather pointless exercise in summing an entire "amount" column from an imaginary "prices" table. This can be done in several ways, first, the built-in L<DBIx::Class::ResultSet::Column> method, by calling B<get_column>. |
280 | |
281 | =over |
282 | |
283 | =item 1. Create a Schema object representing the database you are working with: |
284 | |
285 | my $schema = MyDatabase::Schema->connect('dbi:SQLite:my.db'); |
286 | |
287 | =item 2. Call the B<get_column> method on the resultset for the L<ResultSource|DBIx::Class::ResultSource> you wish to fetch data from, then the B<sum> method: |
288 | |
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289 | my $sum_prices = $schema->resultset('Price')->get_column('amount')->sum(); |
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290 | |
291 | =back |
292 | |
293 | The result is just a number. |
294 | |
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295 | The alternative way uses the B<search> method and is easier to build further refinements into. |
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296 | |
297 | =over |
298 | |
299 | =item 1. Create a Schema object representing the database you are working with: |
300 | |
301 | my $schema = MyDatabase::Schema->connect('dbi:SQLite:my.db'); |
302 | |
303 | =item 2. Call the B<search> method on the resultset for the L<ResultSource|DBIx::Class::ResultSource> you wish to fetch data from: |
304 | |
305 | my $sum_prices_rs = $schema->resultset('Price')->search( |
306 | { }, |
abc32120 |
307 | { columns => { sum_amount => { SUM => 'amount'} } }, |
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308 | ); |
309 | |
310 | =back |
311 | |
312 | The result is a resultset. To fetch the one-row result, call B<single> or B<all>. The resulting Row object will not contain an accessor for the virtual "sum_amount" column, we'll need to fetch it using the Row method B<get_column>. |
313 | |
314 | print $sum_prices_rs->single->get_column('sum_amount'); |
315 | |
316 | =head2 SELECT from JOINed tables |
317 | |
318 | SELECT users.id, username, posts.id, posts.title |
319 | FROM users |
320 | JOIN posts posts ON posts.used_id = users.id |
321 | |
322 | To select data from other tables, use the B<join> attribute to name the table relationships to create a JOIN clause to. |
323 | |
324 | =over |
325 | |
326 | =item 1. Create a Schema object representing the database you are working with: |
327 | |
328 | my $schema = MyDatabase::Schema->connect('dbi:SQLite:my.db'); |
329 | |
330 | =item 2. Call the B<search> method on the resultset of the L<ResultSource|DBIx::Class::ResultSource> you wish to group data on: |
331 | |
332 | my $posts_count_per_user = $schema->resultset('User')->search( |
333 | { }, |
abc32120 |
334 | { columns => [ qw/id username posts.id posts.title/ ], |
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335 | join => 'posts', |
336 | } |
337 | ); |
338 | |
339 | =back |
340 | |
341 | Here "posts" refers to the name of the L<Relationship|DBIx::Class::Relationship> between the "User" source and the "Post" source. |
342 | |
343 | To retrieve the extra data, call the usual relationship accessor: |
344 | |
345 | while( my $row = $sorted_users->next) { |
346 | print "user/post: ", $row->username; |
347 | print $_->title for $row->posts; |
348 | print "\n"; |
349 | } |
350 | |
351 | |
352 | =head2 SELECT with GROUP BY |
353 | |
354 | SELECT users.id, username, COUNT(posts.id) |
355 | FROM users |
356 | JOIN posts posts ON posts.used_id = users.id |
357 | GROUP BY users.id, username; |
358 | |
abc32120 |
359 | To group your results, use the B<group_by> attribute on a B<search> method. We also use the B<columns> attribute to select and name a subset of columns. |
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360 | |
361 | =over |
362 | |
363 | =item 1. Create a Schema object representing the database you are working with: |
364 | |
365 | my $schema = MyDatabase::Schema->connect('dbi:SQLite:my.db'); |
366 | |
1060e1bd |
367 | =item 2. Call the B<search> method on the resultset of the L<ResultSource|DBIx::Class::ResultSource> you wish to group data on: |
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368 | |
369 | my $posts_count_per_user = $schema->resultset('User')->search( |
370 | { }, |
abc32120 |
371 | { columns => [ qw/id username/, { post_count => { count => 'posts.id' } } ], |
6c2a4396 |
372 | join => 'posts', |
373 | group_by => [qw/id username/], |
374 | } |
375 | ); |
376 | |
377 | =back |
378 | |
379 | Here "posts" refers to the name of the L<Relationship|DBIx::Class::Relationship> between the "User" source and the "Post" source. |
380 | |
381 | The results will contain two columns with the usual accessors, "id" and "username", and one with no accessor, as it is a virtual column. |
382 | |
383 | while( my $row = $posts_count_per_user->next) { |
384 | print "user: ", $row->username, " posts: ", $row->get_column('post_count'); |
385 | } |
386 | |
387 | Note: Remember to disambiguate the columns when joining two tables with identical column names. |
388 | |
0e8be732 |
389 | =begin comment |
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390 | |
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391 | Commented out section as ordering by a related source does not work yet. Fix in progress, will comment back in when DBIC is updated. |
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392 | |
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393 | =head2 SELECT with simple ORDER BY |
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394 | |
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395 | SELECT users.id, username, dob, realname, password, posts.title |
396 | FROM users |
397 | JOIN posts posts ON posts.used_id = users.id |
398 | ORDER BY username, posts.title; |
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399 | |
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400 | To sort the results, use the B<order_by> attributes on a B<search> method. Content can of course be ordered by columns in the current table, or in a joined table |
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401 | |
0e8be732 |
402 | =over |
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403 | |
0e8be732 |
404 | =item 1. Create a Schema object representing the database you are working with: |
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405 | |
0e8be732 |
406 | my $schema = MyDatabase::Schema->connect('dbi:SQLite:my.db'); |
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407 | |
0e8be732 |
408 | =item 2. Call the B<search> method on the resultset of the L<ResultSource|DBIx::Class::ResultSource> you wish to sort data on: |
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409 | |
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410 | my $sorted_users = $schema->resultset('User')->search( |
411 | { }, |
412 | { '+columns' => [ qw/posts.id posts.title/ ], |
413 | join => 'posts', |
414 | order_by => [qw/username posts.title/], |
415 | } |
416 | ); |
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417 | |
0e8be732 |
418 | =back |
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419 | |
0e8be732 |
420 | Here "posts" refers to the name of the L<Relationship|DBIx::Class::Relationship> between the "User" source and the "Post" source. |
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421 | |
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422 | The results will be ordered by username, then post title, ready for outputting. |
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423 | |
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424 | Note how we have added the title of each post, this prevents us having to fire off a second query to fetch the post data to output it. The B<+columns> attribute specifies an extended set of columns to fetch, in addition to the columns of the main query table. |
425 | |
426 | To retrieve the extra data, call the usual relationship accessor: |
427 | |
428 | while( my $row = $sorted_users->next) { |
429 | print "user/post: ", $row->username; |
430 | print $_->title for $row->posts; |
431 | print "\n"; |
432 | } |
433 | |
434 | =end comment |
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435 | |
436 | =head2 SELECT with HAVING |
437 | |
438 | SELECT users.id, username, dob |
439 | FROM users |
440 | JOIN posts posts ON posts.used_id = users.id |
abc32120 |
441 | GROUP BY users.id, username, dob |
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442 | HAVING count(posts.id) = 1 |
443 | |
444 | To add a B<having> clause to your query, use the corresponding B<having> attribute. |
445 | |
446 | =over |
447 | |
448 | =item 1. Create a Schema object representing the database you are working with: |
449 | |
450 | my $schema = MyDatabase::Schema->connect('dbi:SQLite:my.db'); |
451 | |
452 | =item 2. Call the B<search> method on the resultset of the L<ResultSource|DBIx::Class::ResultSource> you wish to filter data on: |
453 | |
454 | my $filtered_users = $schema->resultset('User')->search( |
455 | { }, |
abc32120 |
456 | { 'columns' => [ qw/me.id me.username me.dob/ ], |
6c2a4396 |
457 | join => 'posts', |
abc32120 |
458 | group_by => [qw/me.id me.username me.dob/], |
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459 | having => [{ 'posts.id' => 1 }], |
460 | } |
461 | ); |
462 | |
463 | =back |
464 | |
465 | Here "posts" refers to the name of the L<Relationship|DBIx::Class::Relationship> between the "User" source and the "Post" source. |
466 | |
467 | The results will be filtered by the HAVING clause. |
468 | |
469 | =head2 SELECT with DISTINCT |
470 | |
471 | SELECT DISTINCT(posts.title) |
472 | FROM posts |
473 | |
abc32120 |
474 | To produce DISTINCT clauses, we need to use a hashref argument to the list of items passed to the B<columns> attribute. |
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475 | |
476 | =over |
477 | |
478 | =item 1. Create a Schema object representing the database you are working with: |
479 | |
480 | my $schema = MyDatabase::Schema->connect('dbi:SQLite:my.db'); |
481 | |
abc32120 |
482 | =item 2. Call the B<search> method on the resultset of the L<ResultSource|DBIx::Class::ResultSource> you wish to find distinct rows on: |
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483 | |
484 | my $distinct_posts = $schema->resultset('Post')->search( |
485 | { }, |
abc32120 |
486 | { columns => [{ 'd_title' => { distinct => 'me.title' } }], |
6c2a4396 |
487 | } |
488 | ); |
489 | |
490 | =back |
491 | |
abc32120 |
492 | This can also be achieved by using the ResultSet method B<get_column>. The method returns a ResultSetColumn object based on the given column name argument, which can call SQL aggregate functions based upon the column of that data. |
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493 | |
abc32120 |
494 | So we can also do this, for single column DISTINCT clauses: |
495 | |
496 | =over |
497 | |
498 | =item 1. Create a Schema object representing the database you are working with: |
499 | |
500 | my $schema = MyDatabase::Schema->connect('dbi:SQLite:my.db'); |
501 | |
502 | =item 2. Call the B<get_column> method on the resultset of the L<ResultSource|DBIx::Class::ResultSource> you wish to find distinct rows on: |
503 | |
504 | my $rs_column = $schema->resultset('Post')->get_column('title'); |
505 | |
506 | =item 3. Call the B<func> method on the resultset column object and pass it the name of the function to apply: |
507 | |
508 | my $titles = $rs_column->func('distinct'); |
509 | |
510 | =back |
511 | |
512 | The result will be an arrayref of the actual values. If a ResultSet object is needed for further refinement, use B<func_rs> instead. |
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513 | |
514 | =head2 SELECT ... FOR UPDATE |
515 | |
516 | SELECT users.id, users.username, users.dob |
517 | FROM users |
518 | FOR UPDATE |
519 | |
1060e1bd |
520 | To fetch data and lock it for updating from other transactions, use the B<for> attribute and pass it the value B<update>. This should be done inside a L<Transaction|DBIx::Class::Manual::SQLHackers::Transactions>. |
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521 | |
522 | =over |
523 | |
524 | =item 1. Create a Schema object representing the database you are working with: |
525 | |
526 | my $schema = MyDatabase::Schema->connect('dbi:SQLite:my.db'); |
527 | |
528 | =item 2. Call the B<search> method on the resultset of the L<ResultSource|DBIx::Class::ResultSource> you wish to lock data on: |
529 | |
530 | my $locked_posts = $schema->resultset('User')->search( |
531 | { }, |
532 | { columns => [qw/me.id me.username me.dob/], |
533 | for => 'update' |
534 | } |
535 | ); |
536 | |
537 | =back |
538 | |
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539 | The resultset and rows will be returned as normal, and can be used to update the rows without worrying about other processes modifying the table behind your back. |
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540 | |
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541 | =head2 SELECT with LIMIT and OFFSET |
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542 | |
543 | SELECT users.id, users.username |
544 | FROM users |
545 | ORDER BY user.dob DESC |
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546 | LIMIT 10 OFFSET 11; |
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547 | |
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548 | To reduce the set of rows fetched, use the B<rows> and B<page> attributes. The value of B<page> will default to 1, which means no OFFSET will be applied. |
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549 | |
550 | =over |
551 | |
552 | =item 1. Create a Schema object representing the database you are working with: |
553 | |
554 | my $schema = MyDatabase::Schema->connect('dbi:SQLite:my.db'); |
555 | |
556 | =item 2. Call the B<search> method on the resultset of the L<ResultSource|DBIx::Class::ResultSource> you wish to limit data on: |
557 | |
558 | my $limited_posts = $schema->resultset('User')->search( |
559 | { }, |
560 | { columns => [qw/me.id me.username/], |
561 | order_by => { '-desc' => ['user.dob'] }, |
562 | rows => 10, |
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563 | page => 2, |
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564 | } |
565 | ); |
566 | |
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567 | This will return exactly 10 row objects, sorted by descending date of birth of the users, starting at the 11th row of the sorted result. |
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568 | |
569 | =back |