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Overview
Comment: | Update the FAQ. |
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Downloads: | Tarball | ZIP archive |
Timelines: | family | ancestors | descendants | both | trunk |
Files: | files | file ages | folders |
SHA1: |
eb122dda421700e8960eed56befb81c0 |
User & Date: | drh 2014-04-21 13:12:24.415 |
Context
2014-04-21
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18:20 | Update the command-line shell documentation with a discussion of CSV import and export. (check-in: 070bfddab9 user: drh tags: trunk) | |
13:12 | Update the FAQ. (check-in: eb122dda42 user: drh tags: trunk) | |
2014-04-05
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12:04 | Fix a typo on the 3.8.4.3 news page. (check-in: 7401266cf0 user: drh tags: trunk) | |
Changes
Changes to pages/faq.in.
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12 13 14 15 16 17 18 | faq { How do I create an AUTOINCREMENT field. } { <p>Short answer: A column declared [INTEGER PRIMARY KEY] will autoincrement.</p> | | | | | 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 | faq { How do I create an AUTOINCREMENT field. } { <p>Short answer: A column declared [INTEGER PRIMARY KEY] will autoincrement.</p> <p>Longer answer: If you declare a column of a table to be [INTEGER PRIMARY KEY], then whenever you insert a NULL into that column of the table, the NULL is automatically converted into an integer which is one greater than the largest value of that column over all other rows in the table, or 1 if the table is empty. Or, if the largest existing integer key 9223372036854775807 is in use then an unused key value is chosen at random. For example, suppose you have a table like this: <blockquote><pre> CREATE TABLE t1( a INTEGER PRIMARY KEY, b INTEGER ); </pre></blockquote> |
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63 64 65 66 67 68 69 | REAL, TEXT, BLOB, or as NULL. } faq { SQLite lets me insert a string into a database column of type integer! } { <p>This is a feature, not a bug. SQLite uses [dynamic typing]. | | | | | | 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 | REAL, TEXT, BLOB, or as NULL. } faq { SQLite lets me insert a string into a database column of type integer! } { <p>This is a feature, not a bug. SQLite uses [dynamic typing]. It does not enforce data type constraints. Data of any type can (usually) be inserted into any column. You can put arbitrary length strings into integer columns, floating point numbers in boolean columns, or dates in character columns. The [datatype] you assign to a column in the CREATE TABLE command does not restrict what data can be put into that column. Every column is able to hold an arbitrary length string. (There is one exception: Columns of type [INTEGER PRIMARY KEY] may only hold a 64-bit signed integer. An error will result if you try to put anything other than an integer into an [INTEGER PRIMARY KEY] column.)</p> |
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165 166 167 168 169 170 171 | with the SQLITE_THREADSAFE preprocessor macro set to 1. Both the Windows and Linux precompiled binaries in the distribution are compiled this way. If you are unsure if the SQLite library you are linking against is compiled to be threadsafe you can call the [sqlite3_threadsafe()] interface to find out. </p> | | | < < < < < < | < | | < < < < < | < | < | 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 | with the SQLITE_THREADSAFE preprocessor macro set to 1. Both the Windows and Linux precompiled binaries in the distribution are compiled this way. If you are unsure if the SQLite library you are linking against is compiled to be threadsafe you can call the [sqlite3_threadsafe()] interface to find out. </p> <p>SQLite is threadsafe because it uses mutexes to serialize access to common data structures. However, the work of acquiring and releasing these mutexes will slow SQLite down slightly. Hence, if you do not need SQLite to be threadsafe, you should disable the mutexes for maximum performance. See the [threading mode] documentation for additional information.</p> <p>Under Unix, you should not carry an open SQLite database across a fork() system call into the child process.</p> } faq { How do I list all tables/indices contained in an SQLite database } { <p>If you are running the <b>sqlite3</b> command-line access program you can type "<b>.tables</b>" to get a list of all tables. Or you |
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259 260 261 262 263 264 265 | the limits of SQLite.</p> } faq { What is the maximum size of a VARCHAR in SQLite? } { <p>SQLite does not enforce the length of a VARCHAR. You can declare | | | > > > | | > | 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 | the limits of SQLite.</p> } faq { What is the maximum size of a VARCHAR in SQLite? } { <p>SQLite does not enforce the length of a VARCHAR. You can declare a VARCHAR(10) and SQLite will be happy to store a 500-million character string there. And it will keep all 500-million characters intact. Your content is never truncated. SQLite understands the column type of "VARCHAR(<i>N</i>)" to be the same as "TEXT", regardless of the value of <i>N</i>. </p> } faq { Does SQLite support a BLOB type? } { <p>SQLite allows you to store BLOB data in any column, even columns that are declared to hold some other type. BLOBs can even be used as PRIMARY KEYs.</p> } faq { How do I add or delete columns from an existing table in SQLite. } { <p>SQLite has limited <a href="lang_altertable.html">ALTER TABLE</a> support that you can |
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315 316 317 318 319 320 321 | neither is it returned to the operating system.</p> <p>If you delete a lot of data and want to shrink the database file, run the <a href="lang_vacuum.html">VACUUM</a> command. VACUUM will reconstruct the database from scratch. This will leave the database with an empty free-list and a file that is minimal in size. Note, however, that the | | < | | 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 | neither is it returned to the operating system.</p> <p>If you delete a lot of data and want to shrink the database file, run the <a href="lang_vacuum.html">VACUUM</a> command. VACUUM will reconstruct the database from scratch. This will leave the database with an empty free-list and a file that is minimal in size. Note, however, that the VACUUM can take some time to run and it can use up to twice as much temporary disk space as the original file while it is running. </p> <p>An alternative to using the VACUUM command is auto-vacuum mode, enabled using the <a href="pragma.html#pragma_auto_vacuum">auto_vacuum pragma</a>.</p> } faq { Can I use SQLite in my commercial product without paying royalties? } { |
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392 393 394 395 396 397 398 | approximated using the closest binary number available. That approximation is usually very close, but it will be slightly off and in some cases can cause your results to be a little different from what you might expect.</p> } faq { | | | 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 | approximated using the closest binary number available. That approximation is usually very close, but it will be slightly off and in some cases can cause your results to be a little different from what you might expect.</p> } faq { I get some compiler warnings when I compile SQLite. Isn't this a problem? Doesn't it indicate poor code quality? } { <p>Quality assurance in SQLite is done using [test coverage | full-coverage testing], not by compiler warnings or other static code analysis tools. In other words, we verify that SQLite actually gets the correct answer, not that it merely satisfies stylistic constraints. |
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427 428 429 430 431 432 433 | <p>We also run SQLite using [http://valgrind.org | Valgrind] on Linux and verify that it detects no problems.</p> <p>Some people say that we should eliminate all warnings because benign warnings mask real warnings that might arise in future changes. This is true enough. But in reply, the developers observe that all | | | > | | | 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 | <p>We also run SQLite using [http://valgrind.org | Valgrind] on Linux and verify that it detects no problems.</p> <p>Some people say that we should eliminate all warnings because benign warnings mask real warnings that might arise in future changes. This is true enough. But in reply, the developers observe that all warnings have already been fixed in the builds used for SQLite development (various versions of GCC, MSVC, and clang). Compiler warnings usually only arise from compilers or compile-time options that the SQLite developers to not use themselves.</p> } faq { Case-insensitive matching of Unicode characters does not work. } { The default configuration of SQLite only supports case-insensitive comparisons of ASCII characters. The reason for this is that doing |
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523 524 525 526 527 528 529 | rare bugs (see <a href="http://www.sqlite.org/cvstrac/wiki?p=DatabaseCorruption">DatabaseCorruption</a>) and even then the bugs are normally difficult to reproduce. Even if your application crashes in the middle of an update, your database is safe. The database is safe even if your OS crashes or takes a power loss. The crash-resistance of SQLite has been extensively studied and tested and is attested by years of real-world | | | < | < < > | | < | > | < < < < | 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 | rare bugs (see <a href="http://www.sqlite.org/cvstrac/wiki?p=DatabaseCorruption">DatabaseCorruption</a>) and even then the bugs are normally difficult to reproduce. Even if your application crashes in the middle of an update, your database is safe. The database is safe even if your OS crashes or takes a power loss. The crash-resistance of SQLite has been extensively studied and tested and is attested by years of real-world experience by billions of users.</p> <p>That said, there are a number of things that external programs or bugs in your hardware or OS can do to corrupt a database file. See <a href="howtocorrupt.html">How To Corrupt An SQLite DAtabase File</a> for further information. <p>Your can use <a href="pragma.html#pragma_integrity_check">PRAGMA integrity_check</a> to do a thorough but time intensive test of the database integrity.</p> <p>Your can use <a href="pragma.html#pragma_quick_check">PRAGMA quick_check</a> to do a faster but less thorough test of the database integrity.</p> <p>Depending how badly your database is corrupted, you may be able to recover some of the data by using the CLI to dump the schema and contents to a file and then recreate. Unfortunately, once humpty-dumpty falls off the wall, it is generally not possible to put him back together again.</p> } faq { Does SQLite support foreign keys? } { <p> As of version 3.6.19, SQLite supports [foreign key constraints]. But enforcement of foreign key constraints is turned off by default (for backwards compatibility). To enable foreign key constraint enforcements, run [PRAGMA foreign_keys|PRAGMA foreign_keys=ON] or compile with [SQLITE_DEFAULT_FOREIGN_KEYS | -DSQLITE_DEFAULT_FOREIGN_KEYS=1]. } faq { I get a compiler error if I use the SQLITE_OMIT_... compile-time options when building SQLite. } { The [omitfeatures | SQLITE_OMIT_...] compile-time options only work |
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637 638 639 640 641 642 643 644 645 646 647 648 649 650 | that the core public-domain SQLite source code is not described by any ECCN, hence the ECCN should be reported as <b>EAR99</b>. <p>The above is true for the core public-domain SQLite. If you extend SQLite by adding new code, or if you statically link SQLite with your application, that might change the ECCN in your particular case. } # End of questions and answers. ############# hd_puts {<h2>Frequently Asked Questions</h2>} hd_puts {<oL>} | > > > > > > > > > > | 621 622 623 624 625 626 627 628 629 630 631 632 633 634 635 636 637 638 639 640 641 642 643 644 | that the core public-domain SQLite source code is not described by any ECCN, hence the ECCN should be reported as <b>EAR99</b>. <p>The above is true for the core public-domain SQLite. If you extend SQLite by adding new code, or if you statically link SQLite with your application, that might change the ECCN in your particular case. } faq { My query does not return the column name that I expect. Is this a bug? } { If the columns of your result set are named by AS clauses, then SQLite is guaranteed to use the identifer to the right of the AS keyword as the column name. If the result set does not use an AS clause, then SQLite is free to name the column anything it wants. See the [sqlite3_column_name()] documentation for further information. } # End of questions and answers. ############# hd_puts {<h2>Frequently Asked Questions</h2>} hd_puts {<oL>} |
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