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1#
2# Run this Tcl script to generate the pragma.html file.
3#
4set rcsid {$Id: pragma.tcl,v 1.28 2007/08/28 08:19:49 danielk1977 Exp $}
5source common.tcl
6header {Pragma statements supported by SQLite}
7
8proc Section {name {label {}}} {
9 puts "\n<hr />"
10 if {$label!=""} {
11 puts "<a name=\"$label\"></a>"
12 }
13 puts "<h1>$name</h1>\n"
14}
15
16puts {
17<p>The <a href="#syntax">PRAGMA command</a> is a special command used to
18modify the operation of the SQLite library or to query the library for
19internal (non-table) data. The PRAGMA command is issued using the same
20interface as other SQLite commands (e.g. SELECT, INSERT) but is
21different in the following important respects:
22</p>
23<ul>
24<li>Specific pragma statements may be removed and others added in future
25 releases of SQLite. Use with caution!
26<li>No error messages are generated if an unknown pragma is issued.
27 Unknown pragmas are simply ignored. This means if there is a typo in
28 a pragma statement the library does not inform the user of the fact.
29<li>Some pragmas take effect during the SQL compilation stage, not the
30 execution stage. This means if using the C-language sqlite3_prepare(),
31 sqlite3_step(), sqlite3_finalize() API (or similar in a wrapper
32 interface), the pragma may be applied to the library during the
33 sqlite3_prepare() call.
34<li>The pragma command is unlikely to be compatible with any other SQL
35 engine.
36</ul>
37
38<p>The available pragmas fall into four basic categories:</p>
39<ul>
40<li>Pragmas used to <a href="#modify">modify the operation</a> of the
41 SQLite library in some manner, or to query for the current mode of
42 operation.
43<li>Pragmas used to <a href="#schema">query the schema</a> of the current
44 database.
45<li>Pragmas used to <a href="#version">query or modify the databases two
46 version values</a>, the schema-version and the user-version.
47<li>Pragmas used to <a href="#debug">debug the library</a> and verify that
48 database files are not corrupted.
49</ul>
50}
51
52Section {PRAGMA command syntax} syntax
53
54Syntax {sql-statement} {
55PRAGMA <name> [= <value>] |
56PRAGMA <function>(<arg>)
57}
58
59puts {
60<p>The pragmas that take an integer <b><i>value</i></b> also accept
61symbolic names. The strings "<b>on</b>", "<b>true</b>", and "<b>yes</b>"
62are equivalent to <b>1</b>. The strings "<b>off</b>", "<b>false</b>",
63and "<b>no</b>" are equivalent to <b>0</b>. These strings are case-
64insensitive, and do not require quotes. An unrecognized string will be
65treated as <b>1</b>, and will not generate an error. When the <i>value</i>
66is returned it is as an integer.</p>
67}
68
69Section {Pragmas to modify library operation} modify
70
71puts {
72<ul>
73<a name="pragma_auto_vacuum"></a>
74<li><p><b>PRAGMA auto_vacuum;<br>
75 PRAGMA auto_vacuum = </b>
76 <i>0 | none | 1 | full | 2 | incremental</i><b>;</b></p>
77 <p>Query or set the auto-vacuum flag in the database.</p>
78
79 <p>Normally, (that is to say when auto_vacuum is 0 or "none")
80 when a transaction that deletes data from a database is
81 committed, the database file remains the same size. Unused database file
82 pages are added to a "freelist" are reused for subsequent inserts. The
83 database file does not shrink.
84 In this mode the <a href="lang_vacuum.html">VACUUM</a>
85 command can be used to reclaim unused space.</p>
86
87 <p>When the auto-vacuum flag is 1 (full), the freelist pages are
88 moved to the end of the file and the file is truncated to remove
89 the freelist pages at every commit.
90 Note, however, that auto-vacuum only truncates the freelist pages
91 from the file. Auto-vacuum does not defragment the database nor
92 repack individual database pages the way that the
93 <a href="lang_vacuum.html">VACUUM</a> command does. In fact, because
94 it moves pages around within the file, auto-vacuum can actually
95 make fragmentation worse.</p>
96
97 <p>Auto-vacuuming is only possible if the database stores some
98 additional information that allows each database page to be
99 traced backwards to its referer. Therefore, auto-vacuuming must
100 be turned on before any tables are created. It is not possible
101 to enable or disable auto-vacuum after a table has been created.</p>
102
103 <p>When the value of auto-vacuum is 2 (incremental) then the additional
104 information needed to do autovacuuming is stored in the database file
105 but autovacuuming does not occur automatically at each commit as it
106 does with auto_vacuum==full. In incremental mode, the separate
107 <a href="#pragma_incremental_vacuum">incremental_vacuum</a> pragma must
108 be invoked to cause the vacuum to occur.</p>
109
110 <p>The database connection can be changed between full and incremental
111 autovacuum mode at will. However, the connection cannot be changed
112 in and out of the "none" mode after any table has been created in the
113 database.
114 </p></li>
115
116<a name="pragma_cache_size"></a>
117<li><p><b>PRAGMA cache_size;
118 <br>PRAGMA cache_size = </b><i>Number-of-pages</i><b>;</b></p>
119 <p>Query or change the maximum number of database disk pages that SQLite
120 will hold in memory at once. Each page uses about 1.5K of memory.
121 The default cache size is 2000. If you are doing UPDATEs or DELETEs
122 that change many rows of a database and you do not mind if SQLite
123 uses more memory, you can increase the cache size for a possible speed
124 improvement.</p>
125 <p>When you change the cache size using the cache_size pragma, the
126 change only endures for the current session. The cache size reverts
127 to the default value when the database is closed and reopened. Use
128 the <a href="#pragma_default_cache_size"><b>default_cache_size</b></a>
129 pragma to check the cache size permanently.</p></li>
130
131<a name="pragma_case_sensitive_like"></a>
132<li><p><b>PRAGMA case_sensitive_like;
133 <br>PRAGMA case_sensitive_like = </b><i>0 | 1</i><b>;</b></p>
134 <p>The default behavior of the LIKE operator is to ignore case
135 for latin1 characters. Hence, by default <b>'a' LIKE 'A'</b> is
136 true. The case_sensitive_like pragma can be turned on to change
137 this behavior. When case_sensitive_like is enabled,
138 <b>'a' LIKE 'A'</b> is false but <b>'a' LIKE 'a'</b> is still true.</p>
139 </li>
140
141<a name="pragma_count_changes"></a>
142<li><p><b>PRAGMA count_changes;
143 <br>PRAGMA count_changes = </b><i>0 | 1</i><b>;</b></p>
144 <p>Query or change the count-changes flag. Normally, when the
145 count-changes flag is not set, INSERT, UPDATE and DELETE statements
146 return no data. When count-changes is set, each of these commands
147 returns a single row of data consisting of one integer value - the
148 number of rows inserted, modified or deleted by the command. The
149 returned change count does not include any insertions, modifications
150 or deletions performed by triggers.</p>
151
152<a name="pragma_default_cache_size"></a>
153<li><p><b>PRAGMA default_cache_size;
154 <br>PRAGMA default_cache_size = </b><i>Number-of-pages</i><b>;</b></p>
155 <p>Query or change the maximum number of database disk pages that SQLite
156 will hold in memory at once. Each page uses 1K on disk and about
157 1.5K in memory.
158 This pragma works like the
159 <a href="#pragma_cache_size"><b>cache_size</b></a>
160 pragma with the additional
161 feature that it changes the cache size persistently. With this pragma,
162 you can set the cache size once and that setting is retained and reused
163 every time you reopen the database.</p></li>
164
165<a name="pragma_default_synchronous"></a>
166<li><p><b>PRAGMA default_synchronous;</b></p>
167 <p>This pragma was available in version 2.8 but was removed in version
168 3.0. It is a dangerous pragma whose use is discouraged. To help
169 dissuide users of version 2.8 from employing this pragma, the documentation
170 will not tell you what it does.</p></li>
171
172
173<a name="pragma_empty_result_callbacks"></a>
174<li><p><b>PRAGMA empty_result_callbacks;
175 <br>PRAGMA empty_result_callbacks = </b><i>0 | 1</i><b>;</b></p>
176 <p>Query or change the empty-result-callbacks flag.</p>
177 <p>The empty-result-callbacks flag affects the sqlite3_exec API only.
178 Normally, when the empty-result-callbacks flag is cleared, the
179 callback function supplied to the sqlite3_exec() call is not invoked
180 for commands that return zero rows of data. When empty-result-callbacks
181 is set in this situation, the callback function is invoked exactly once,
182 with the third parameter set to 0 (NULL). This is to enable programs
183 that use the sqlite3_exec() API to retrieve column-names even when
184 a query returns no data.
185 </p>
186
187<a name="pragma_encoding"></a>
188<li><p><b>PRAGMA encoding;
189 <br>PRAGMA encoding = "UTF-8";
190 <br>PRAGMA encoding = "UTF-16";
191 <br>PRAGMA encoding = "UTF-16le";
192 <br>PRAGMA encoding = "UTF-16be";</b></p>
193 <p>In first form, if the main database has already been
194 created, then this pragma returns the text encoding used by the
195 main database, one of "UTF-8", "UTF-16le" (little-endian UTF-16
196 encoding) or "UTF-16be" (big-endian UTF-16 encoding). If the main
197 database has not already been created, then the value returned is the
198 text encoding that will be used to create the main database, if
199 it is created by this session.</p>
200 <p>The second and subsequent forms of this pragma are only useful if
201 the main database has not already been created. In this case the
202 pragma sets the encoding that the main database will be created with if
203 it is created by this session. The string "UTF-16" is interpreted
204 as "UTF-16 encoding using native machine byte-ordering". If the second
205 and subsequent forms are used after the database file has already
206 been created, they have no effect and are silently ignored.</p>
207
208 <p>Once an encoding has been set for a database, it cannot be changed.</p>
209
210 <p>Databases created by the ATTACH command always use the same encoding
211 as the main database.</p>
212</li>
213
214<a name="pragma_full_column_names"></a>
215<li><p><b>PRAGMA full_column_names;
216 <br>PRAGMA full_column_names = </b><i>0 | 1</i><b>;</b></p>
217 <p>Query or change the full-column-names flag. This flag affects
218 the way SQLite names columns of data returned by SELECT statements
219 when the expression for the column is a table-column name or the
220 wildcard "*". Normally, such result columns are named
221 &lt;table-name/alias&gt;&lt;column-name&gt; if the SELECT statement joins
222 two or
223 more tables together, or simply &lt;column-name&gt; if the SELECT
224 statement queries a single table. When the full-column-names flag
225 is set, such columns are always named &lt;table-name/alias&gt;
226 &lt;column-name&gt; regardless of whether or not a join is performed.
227 </p>
228 <p>If both the short-column-names and full-column-names are set,
229 then the behaviour associated with the full-column-names flag is
230 exhibited.
231 </p>
232</li>
233
234<a name="pragma_fullfsync"></a>
235<li><p><b>PRAGMA fullfsync
236 <br>PRAGMA fullfsync = </b><i>0 | 1</i><b>;</b></p>
237 <p>Query or change the fullfsync flag. This flag affects
238 determines whether or not the F_FULLFSYNC syncing method is used
239 on systems that support it. The default value is off. As of this
240 writing (2006-02-10) only Mac OS X supports F_FULLFSYNC.
241 </p>
242</li>
243
244<a name="pragma_incremental_vacuum"></a>
245<li><p><b>PRAGMA incremental_vacuum</b><i>(N)</i><b>;</b></p>
246 <p>The incremental_vacuum pragma causes up to <i>N</i> pages to
247 be removed from the freelist. The database file is truncated by
248 the same amount. The incremental_vacuum pragma has no effect if
249 the database is not in
250 <a href="#pragma_auto_vacuum">auto_vacuum==incremental</a> mode
251 or if there are no pages on the freelist. If there are fewer than
252 <i>N</i> pages on the freelist, then the entire freelist is cleared.</p>
253
254 <p>As of version 3.4.0 (the first version that supports
255 incremental_vacuum) this feature is still experimental. Possible
256 future changes include enhancing incremental vacuum to do
257 defragmentation and node repacking just as the full-blown
258 <a href="lang_vacuum.html">VACUUM</a> command does. And
259 incremental vacuum may be promoted from a pragma to a separate
260 SQL command, or perhaps some variation on the VACUUM command.
261 Programmers are cautioned to not become enamored with the
262 current syntax or functionality as it is likely to change.</p>
263</li>
264
265
266<a name="pragma_legacy_file_format"></a>
267<li><p><b>PRAGMA legacy_file_format;
268 <br>PRAGMA legacy_file_format = <i>ON | OFF</i></b></p>
269 <p>This pragma sets or queries the value of the legacy_file_format
270 flag. When this flag is on, new SQLite databases are created in
271 a file format that is readable and writable by all versions of
272 SQLite going back to 3.0.0. When the flag is off, new databases
273 are created using the latest file format which might not be
274 readable or writable by older versions of SQLite.</p>
275
276 <p>This flag only affects newly created databases. It has no
277 effect on databases that already exist.</p>
278</li>
279
280<a name="pragma_locking_mode"></a>
281<li><p><b>PRAGMA locking_mode;
282 <br>PRAGMA locking_mode = <i>NORMAL | EXCLUSIVE</i></b></p>
283 <p>This pragma sets or queries the database connection locking-mode.
284 The locking-mode is either NORMAL or EXCLUSIVE.
285
286 <p>In NORMAL locking-mode (the default), a database connection
287 unlocks the database file at the conclusion of each read or
288 write transaction. When the locking-mode is set to EXCLUSIVE, the
289 database connection never releases file-locks. The first time the
290 database is read in EXCLUSIVE mode, a shared lock is obtained and
291 held. The first time the database is written, an exclusive lock is
292 obtained and held.</p>
293
294 <p>Database locks obtained by a connection in EXCLUSIVE mode may be
295 released either by closing the database connection, or by setting the
296 locking-mode back to NORMAL using this pragma and then accessing the
297 database file (for read or write). Simply setting the locking-mode to
298 NORMAL is not enough - locks are not be released until the next time
299 the database file is accessed.</p>
300
301 <p>There are two reasons to set the locking-mode to EXCLUSIVE. One
302 is if the application actually wants to prevent other processes from
303 accessing the database file. The other is that a small number of
304 filesystem operations are saved by optimizations enabled in this
305 mode. This may be significant in embedded environments.</p>
306
307 <p>When the locking_mode pragma specifies a particular database,
308 for example:</p>
309
310 <blockquote>
311PRAGMA <b>main.</b>locking_mode=EXCLUSIVE;
312 </blockquote>
313
314 <p>Then the locking mode applies only to the named database. If no
315 database name qualifier preceeds the "locking_mode" keyword then
316 the locking mode is applied to all databases, including any new
317 databases added by subsequent <a href="lang_attach.html">ATTACH</a>
318 commands.</p>
319
320 <p>The "temp" database (in which TEMP tables and indices are stored)
321 always uses exclusive locking mode. The locking mode of temp cannot
322 be changed. All other databases use the normal locking mode by default
323 and are affected by this pragma.</p>
324</li>
325
326<a name="pragma_page_size"></a>
327<li><p><b>PRAGMA page_size;
328 <br>PRAGMA page_size = </b><i>bytes</i><b>;</b></p>
329 <p>Query or set the page-size of the database. The page-size
330 may only be set if the database has not yet been created. The page
331 size must be a power of two greater than or equal to 512 and less
332 than or equal to 8192. The upper limit may be modified by setting
333 the value of macro SQLITE_MAX_PAGE_SIZE during compilation. The
334 maximum upper bound is 32768.
335 </p>
336</li>
337
338<a name="pragma_max_page_count"></a>
339<li><p><b>PRAGMA max_page_count;
340 <br>PRAGMA max_page_count = </b><i>N</i><b>;</b></p>
341 <p>Query or set the maximum number of pages in the database file.
342 Both forms of the pragma return the maximum page count. The second
343 form attempts to modify the maximum page count. The maximum page
344 count cannot be reduced below the current database size.
345 </p>
346</li>
347
348<a name="pragma_read_uncommitted"></a>
349<li><p><b>PRAGMA read_uncommitted;
350 <br>PRAGMA read_uncommitted = </b><i>0 | 1</i><b>;</b></p>
351 <p>Query, set, or clear READ UNCOMMITTED isolation. The default isolation
352 level for SQLite is SERIALIZABLE. Any process or thread can select
353 READ UNCOMMITTED isolation, but SERIALIZABLE will still be used except
354 between connections that share a common page and schema cache.
355 Cache sharing is enabled using the
356 <a href="capi3ref.html#sqlite3_enable_shared_cache">
357 sqlite3_enable_shared_cache()</a> API and is only available between
358 connections running the same thread. Cache sharing is off by default.
359 </p>
360</li>
361
362<a name="pragma_short_column_names"></a>
363<li><p><b>PRAGMA short_column_names;
364 <br>PRAGMA short_column_names = </b><i>0 | 1</i><b>;</b></p>
365 <p>Query or change the short-column-names flag. This flag affects
366 the way SQLite names columns of data returned by SELECT statements
367 when the expression for the column is a table-column name or the
368 wildcard "*". Normally, such result columns are named
369 &lt;table-name/alias&gt;lt;column-name&gt; if the SELECT statement
370 joins two or more tables together, or simply &lt;column-name&gt; if
371 the SELECT statement queries a single table. When the short-column-names
372 flag is set, such columns are always named &lt;column-name&gt;
373 regardless of whether or not a join is performed.
374 </p>
375 <p>If both the short-column-names and full-column-names are set,
376 then the behaviour associated with the full-column-names flag is
377 exhibited.
378 </p>
379</li>
380
381<a name="pragma_synchronous"></a>
382<li><p><b>PRAGMA synchronous;
383 <br>PRAGMA synchronous = FULL; </b>(2)<b>
384 <br>PRAGMA synchronous = NORMAL; </b>(1)<b>
385 <br>PRAGMA synchronous = OFF; </b>(0)</p>
386 <p>Query or change the setting of the "synchronous" flag.
387 The first (query) form will return the setting as an
388 integer. When synchronous is FULL (2), the SQLite database engine will
389 pause at critical moments to make sure that data has actually been
390 written to the disk surface before continuing. This ensures that if
391 the operating system crashes or if there is a power failure, the database
392 will be uncorrupted after rebooting. FULL synchronous is very
393 safe, but it is also slow.
394 When synchronous is NORMAL, the SQLite database
395 engine will still pause at the most critical moments, but less often
396 than in FULL mode. There is a very small (though non-zero) chance that
397 a power failure at just the wrong time could corrupt the database in
398 NORMAL mode. But in practice, you are more likely to suffer
399 a catastrophic disk failure or some other unrecoverable hardware
400 fault.
401 With synchronous OFF (0), SQLite continues without pausing
402 as soon as it has handed data off to the operating system.
403 If the application running SQLite crashes, the data will be safe, but
404 the database might become corrupted if the operating system
405 crashes or the computer loses power before that data has been written
406 to the disk surface. On the other hand, some
407 operations are as much as 50 or more times faster with synchronous OFF.
408 </p>
409 <p>In SQLite version 2, the default value is NORMAL. For version 3, the
410 default was changed to FULL.
411 </p>
412</li>
413
414
415<a name="pragma_temp_store"></a>
416<li><p><b>PRAGMA temp_store;
417 <br>PRAGMA temp_store = DEFAULT;</b> (0)<b>
418 <br>PRAGMA temp_store = FILE;</b> (1)<b>
419 <br>PRAGMA temp_store = MEMORY;</b> (2)</p>
420 <p>Query or change the setting of the "<b>temp_store</b>" parameter.
421 When temp_store is DEFAULT (0), the compile-time C preprocessor macro
422 TEMP_STORE is used to determine where temporary tables and indices
423 are stored. When
424 temp_store is MEMORY (2) temporary tables and indices are kept in memory.
425 When temp_store is FILE (1) temporary tables and indices are stored
426 in a file. The <a href="#pragma_temp_store_directory">
427 temp_store_directory</a> pragma can be used to specify the directory
428 containing this file.
429 <b>FILE</b> is specified. When the temp_store setting is changed,
430 all existing temporary tables, indices, triggers, and views are
431 immediately deleted.</p>
432
433 <p>It is possible for the library compile-time C preprocessor symbol
434 TEMP_STORE to override this pragma setting. The following table summarizes
435 the interaction of the TEMP_STORE preprocessor macro and the
436 temp_store pragma:</p>
437
438 <blockquote>
439 <table cellpadding="2" border="1">
440 <tr><th valign="bottom">TEMP_STORE</th>
441 <th valign="bottom">PRAGMA<br>temp_store</th>
442 <th>Storage used for<br>TEMP tables and indices</th></tr>
443 <tr><td align="center">0</td>
444 <td align="center"><em>any</em></td>
445 <td align="center">file</td></tr>
446 <tr><td align="center">1</td>
447 <td align="center">0</td>
448 <td align="center">file</td></tr>
449 <tr><td align="center">1</td>
450 <td align="center">1</td>
451 <td align="center">file</td></tr>
452 <tr><td align="center">1</td>
453 <td align="center">2</td>
454 <td align="center">memory</td></tr>
455 <tr><td align="center">2</td>
456 <td align="center">0</td>
457 <td align="center">memory</td></tr>
458 <tr><td align="center">2</td>
459 <td align="center">1</td>
460 <td align="center">file</td></tr>
461 <tr><td align="center">2</td>
462 <td align="center">2</td>
463 <td align="center">memory</td></tr>
464 <tr><td align="center">3</td>
465 <td align="center"><em>any</em></td>
466 <td align="center">memory</td></tr>
467 </table>
468 </blockquote>
469 </li>
470 <br>
471
472<a name="pragma_temp_store_directory"></a>
473<li><p><b>PRAGMA temp_store_directory;
474 <br>PRAGMA temp_store_directory = 'directory-name';</b></p>
475 <p>Query or change the setting of the "temp_store_directory" - the
476 directory where files used for storing temporary tables and indices
477 are kept. This setting lasts for the duration of the current connection
478 only and resets to its default value for each new connection opened.
479
480 <p>When the temp_store_directory setting is changed, all existing temporary
481 tables, indices, triggers, and viewers are immediately deleted. In
482 practice, temp_store_directory should be set immediately after the
483 database is opened. </p>
484
485 <p>The value <i>directory-name</i> should be enclosed in single quotes.
486 To revert the directory to the default, set the <i>directory-name</i> to
487 an empty string, e.g., <i>PRAGMA temp_store_directory = ''</i>. An
488 error is raised if <i>directory-name</i> is not found or is not
489 writable. </p>
490
491 <p>The default directory for temporary files depends on the OS. For
492 Unix/Linux/OSX, the default is the is the first writable directory found
493 in the list of: <b>/var/tmp, /usr/tmp, /tmp,</b> and <b>
494 <i>current-directory</i></b>. For Windows NT, the default
495 directory is determined by Windows, generally
496 <b>C:\Documents and Settings\<i>user-name</i>\Local Settings\Temp\</b>.
497 Temporary files created by SQLite are unlinked immediately after
498 opening, so that the operating system can automatically delete the
499 files when the SQLite process exits. Thus, temporary files are not
500 normally visible through <i>ls</i> or <i>dir</i> commands.</p>
501
502 </li>
503</ul>
504}
505
506Section {Pragmas to query the database schema} schema
507
508puts {
509<ul>
510<a name="pragma_database_list"></a>
511<li><p><b>PRAGMA database_list;</b></p>
512 <p>For each open database, invoke the callback function once with
513 information about that database. Arguments include the index and
514 the name the database was attached with. The first row will be for
515 the main database. The second row will be for the database used to
516 store temporary tables.</p></li>
517
518<a name="pragma_foreign_key_list"></a>
519<li><p><b>PRAGMA foreign_key_list(</b><i>table-name</i><b>);</b></p>
520 <p>For each foreign key that references a column in the argument
521 table, invoke the callback function with information about that
522 foreign key. The callback function will be invoked once for each
523 column in each foreign key.</p></li>
524
525<a name="pragma_freelist_count"></a>
526<li><p><b>PRAGMA [database].freelist_count;</b></p>
527 <p>Return the number of unused pages in the database file. Running
528 a <a href="#pragma_incremental_vacuum">"PRAGMA incremental_vaccum(N);"</a>
529 command with a large value of N will shrink the database file by this
530 number of pages. </p></li>
531
532<a name="pragma_index_info"></a>
533<li><p><b>PRAGMA index_info(</b><i>index-name</i><b>);</b></p>
534 <p>For each column that the named index references, invoke the
535 callback function
536 once with information about that column, including the column name,
537 and the column number.</p></li>
538
539<a name="pragma_index_list"></a>
540<li><p><b>PRAGMA index_list(</b><i>table-name</i><b>);</b></p>
541 <p>For each index on the named table, invoke the callback function
542 once with information about that index. Arguments include the
543 index name and a flag to indicate whether or not the index must be
544 unique.</p></li>
545
546<a name="pragma_table_info"></a>
547<li><p><b>PRAGMA table_info(</b><i>table-name</i><b>);</b></p>
548 <p>For each column in the named table, invoke the callback function
549 once with information about that column, including the column name,
550 data type, whether or not the column can be NULL, and the default
551 value for the column.</p></li>
552</ul>
553}
554
555Section {Pragmas to query/modify version values} version
556
557puts {
558
559<ul>
560<a name="pragma_schema_version"></a>
561<a name="pragma_user_version"></a>
562<li><p><b>PRAGMA [database.]schema_version;
563 <br>PRAGMA [database.]schema_version = </b><i>integer </i><b>;
564 <br>PRAGMA [database.]user_version;
565 <br>PRAGMA [database.]user_version = </b><i>integer </i><b>;</b>
566
567
568<p> The pragmas schema_version and user_version are used to set or get
569 the value of the schema-version and user-version, respectively. Both
570 the schema-version and the user-version are 32-bit signed integers
571 stored in the database header.</p>
572
573<p> The schema-version is usually only manipulated internally by SQLite.
574 It is incremented by SQLite whenever the database schema is modified
575 (by creating or dropping a table or index). The schema version is
576 used by SQLite each time a query is executed to ensure that the
577 internal cache of the schema used when compiling the SQL query matches
578 the schema of the database against which the compiled query is actually
579 executed. Subverting this mechanism by using "PRAGMA schema_version"
580 to modify the schema-version is potentially dangerous and may lead
581 to program crashes or database corruption. Use with caution!</p>
582
583<p> The user-version is not used internally by SQLite. It may be used by
584 applications for any purpose.</p>
585</li>
586</ul>
587}
588
589Section {Pragmas to debug the library} debug
590
591puts {
592<ul>
593<a name="pragma_integrity_check"></a>
594<li><p><b>PRAGMA integrity_check;
595 <br>PRAGMA integrity_check(</b><i>integer</i><b>)</b></p>
596 <p>The command does an integrity check of the entire database. It
597 looks for out-of-order records, missing pages, malformed records, and
598 corrupt indices.
599 If any problems are found, then strings are returned (as multiple
600 rows with a single column per row) which describe
601 the problems. At most <i>integer</i> errors will be reported
602 before the analysis quits. The default value for <i>integer</i>
603 is 100. If no errors are found, a single row with the value "ok" is
604 returned.</p></li>
605
606<a name="pragma_parser_trace"></a>
607<li><p><b>PRAGMA parser_trace = ON; </b>(1)<b>
608 <br>PRAGMA parser_trace = OFF;</b> (0)</p>
609 <p>Turn tracing of the SQL parser inside of the
610 SQLite library on and off. This is used for debugging.
611 This only works if the library is compiled without the NDEBUG macro.
612 </p></li>
613
614<a name="pragma_vdbe_trace"></a>
615<li><p><b>PRAGMA vdbe_trace = ON; </b>(1)<b>
616 <br>PRAGMA vdbe_trace = OFF;</b> (0)</p>
617 <p>Turn tracing of the virtual database engine inside of the
618 SQLite library on and off. This is used for debugging. See the
619 <a href="vdbe.html#trace">VDBE documentation</a> for more
620 information.</p></li>
621
622<a name="pragma_vdbe_listing"></a>
623<li><p><b>PRAGMA vdbe_listing = ON; </b>(1)<b>
624 <br>PRAGMA vdbe_listing = OFF;</b> (0)</p>
625 <p>Turn listings of virtual machine programs on and off.
626 With listing is on, the entire content of a program is printed
627 just prior to beginning execution. This is like automatically
628 executing an EXPLAIN prior to each statement. The statement
629 executes normally after the listing is printed.
630 This is used for debugging. See the
631 <a href="vdbe.html#trace">VDBE documentation</a> for more
632 information.</p></li>
633</ul>
634
635}
generated by cgit v1.1 at 2025-04-25 06:37:37 +0000