SQLite: Check-in [18b31b7a]

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Overview

Comment:	Fix for ticket #26: Document the fact that CREATE TABLE might not be immediately visible to other processes that are holding the database open. (CVS 544)
Downloads:	Tarball \| ZIP archive \| SQL archive
Timelines:	family \| ancestors \| descendants \| both \| trunk
Files:	files \| file ages \| folders
SHA1:	18b31b7ab90ab330e271e0ed5d316f63846845be
User & Date:	drh 2002-04-25 00:21:50

Context

2002-04-25
11:45		Added the "encode.c" source file that contains two utility subroutines that can be used to encode binary data for use in INSERT and UPDATE statements. This is just an initial checking. The code has not yet been integrated into the library. (CVS 545) (check-in: 57f7c597 user: drh tags: trunk)
00:21		Fix for ticket #26: Document the fact that CREATE TABLE might not be immediately visible to other processes that are holding the database open. (CVS 544) (check-in: 18b31b7a user: drh tags: trunk)
2002-04-23
17:10		Fix for ticket #22: In the code generator for compound SELECT statements, take care not to generate column name headers if the output is an intermediate table. Otherwise the column headers are not generated correctly if a compound SELECT statement appears as an expression in part of the WHERE clause. (CVS 543) (check-in: a06d9acd user: drh tags: trunk)

Changes

Hide Diffs Unified Diffs Ignore Whitespace Patch

Changes to www/faq.tcl.

#
# Run this script to generated a faq.html output file
#
set rcsid {$Id: faq.tcl,v 1.9 2002/03/23 00:31:29 drh Exp $}

puts {<html>
<head>
  <title>SQLite Frequently Asked Questions</title>
</head>
<body bgcolor="white">
<h1 align="center">Frequently Asked Questions</h1>
................................................................................
  earlier.</p>

  <p>Beginning with version 2.2.3, there is a new API function named
  <b>sqlite_last_insert_rowid()</b> which will return the integer key
  for the most recent insert operation.  See the API documentation for
  details.</p>
}















faq {
  SQLite lets me insert a string into a database column of type integer!
} {
  <p>This is a feature, not a bug.  SQLite is typeless.  Any data can be
  inserted into any column.  You can put arbitrary length strings into
  integer columns, floating point numbers in boolean columns, or dates
................................................................................
  server instead of SQLite.</p>

  <p>When SQLite tries to access a file that is locked by another
  process, the default behavior is to return SQLITE_BUSY.  You can
  adjust this behavior from C code using the <b>sqlite_busy_handler()</b> or
  <b>sqlite_busy_timeout()</b> API functions.  See the API documentation
  for details.</p>






}

faq {
  Is SQLite threadsafe?
} {
  <p>Yes.  Sometimes.  In order to be thread-safe, SQLite must be compiled
  with the THREADSAFE preprocessor macro set to 1.  In the default
................................................................................
  recompile.</p>

  <p>"Threadsafe" in the previous paragraph means that two or more threads
  can run SQLite at the same time on different "<b>sqlite</b>" structures
  returned from separate calls to <b>sqlite_open()</b>.  It is never safe
  to use the same <b>sqlite</b> structure pointer simultaneously in two
  or more threads.</p>






}

faq {
  How do I list all tables/indices contained in an SQLite database
} {
  <p>If you are running the <b>sqlite</b> command-line access program
  you can type "<b>.tables</b>" to get a list of all tables.  Or you
................................................................................
  CREATE TABLE, CREATE INDEX, DROP TABLE, and DROP INDEX commands.</p>

  <p>Temporary tables do not appear in the SQLITE_MASTER table.  At this time
  there is no way to get a listing of temporary tables and indices.</p>
}

faq {
  Are there any known size limits to SQLite databases.
} {
  <p>Internally, SQLite can handle databases up to 2^40 bytes (1 terabyte)
  in size.  But the backend interface to POSIX and Win32 limits files to
  2^31 (2 gigabytes).</p>

  <p>SQLite arbitrarily limits the amount of data in one row to 1 megabyte.
  There is a single #define in the source code that can be changed to raise
................................................................................
  limit due to the file size constraint.</p>

  <p>The name and "CREATE TABLE" statement for a table must fit entirely
  within a 1-megabyte row of the SQLITE_MASTER table.  Other than this,
  there are no constraints on the length of the name of a table, or on the
  number of columns, etc.  Indices are similarly unconstrained.</p>
}































faq {
  How do I add or delete columns from an existing table in SQLite.
} {
  <p>SQLite does not support the "ALTER TABLE" SQL command.  If you
  what to change the structure of a table, you have to recreate the
  table.  You can save existing data to a temporary table, drop the




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#
# Run this script to generated a faq.html output file
#
set rcsid {$Id: faq.tcl,v 1.10 2002/04/25 00:21:50 drh Exp $}

puts {<html>
<head>
  <title>SQLite Frequently Asked Questions</title>
</head>
<body bgcolor="white">
<h1 align="center">Frequently Asked Questions</h1>
................................................................................
  earlier.</p>

  <p>Beginning with version 2.2.3, there is a new API function named
  <b>sqlite_last_insert_rowid()</b> which will return the integer key
  for the most recent insert operation.  See the API documentation for
  details.</p>
}

faq {
  What datatypes does SQLite support?
} {
  <p>SQLite is typeless. All data is stored as null-terminated strings.
  The datatype information that follows the column name in CREATE TABLE
  statements is ignored (mostly).  You can put any type of data you want
  into any column, without regard to the declared datatype of that column.
  </p>

  <p>An exception to this rule is a column of type INTEGER PRIMARY KEY.
  Such columns must hold an integer.  An attempt to put a non-integer
  value into an INTEGER PRIMARY KEY column will generate an error.</p>
}

faq {
  SQLite lets me insert a string into a database column of type integer!
} {
  <p>This is a feature, not a bug.  SQLite is typeless.  Any data can be
  inserted into any column.  You can put arbitrary length strings into
  integer columns, floating point numbers in boolean columns, or dates
................................................................................
  server instead of SQLite.</p>

  <p>When SQLite tries to access a file that is locked by another
  process, the default behavior is to return SQLITE_BUSY.  You can
  adjust this behavior from C code using the <b>sqlite_busy_handler()</b> or
  <b>sqlite_busy_timeout()</b> API functions.  See the API documentation
  for details.</p>

  <p>If two or more processes have the same database open and one
  process creates a new table or index, the other processes might
  not be able to see the new table right away.  You might have to
  get the other processes to close and reopen their connection to
  the database before they will be able to see the new table.</p>
}

faq {
  Is SQLite threadsafe?
} {
  <p>Yes.  Sometimes.  In order to be thread-safe, SQLite must be compiled
  with the THREADSAFE preprocessor macro set to 1.  In the default
................................................................................
  recompile.</p>

  <p>"Threadsafe" in the previous paragraph means that two or more threads
  can run SQLite at the same time on different "<b>sqlite</b>" structures
  returned from separate calls to <b>sqlite_open()</b>.  It is never safe
  to use the same <b>sqlite</b> structure pointer simultaneously in two
  or more threads.</p>

  <p>Note that if two or more threads have the same database open and one
  thread creates a new table or index, the other threads might
  not be able to see the new table right away.  You might have to
  get the other threads to close and reopen their connection to
  the database before they will be able to see the new table.</p>
}

faq {
  How do I list all tables/indices contained in an SQLite database
} {
  <p>If you are running the <b>sqlite</b> command-line access program
  you can type "<b>.tables</b>" to get a list of all tables.  Or you
................................................................................
  CREATE TABLE, CREATE INDEX, DROP TABLE, and DROP INDEX commands.</p>

  <p>Temporary tables do not appear in the SQLITE_MASTER table.  At this time
  there is no way to get a listing of temporary tables and indices.</p>
}

faq {
  Are there any known size limits to SQLite databases?
} {
  <p>Internally, SQLite can handle databases up to 2^40 bytes (1 terabyte)
  in size.  But the backend interface to POSIX and Win32 limits files to
  2^31 (2 gigabytes).</p>

  <p>SQLite arbitrarily limits the amount of data in one row to 1 megabyte.
  There is a single #define in the source code that can be changed to raise
................................................................................
  limit due to the file size constraint.</p>

  <p>The name and "CREATE TABLE" statement for a table must fit entirely
  within a 1-megabyte row of the SQLITE_MASTER table.  Other than this,
  there are no constraints on the length of the name of a table, or on the
  number of columns, etc.  Indices are similarly unconstrained.</p>
}

faq {
  What is the maximum size of a VARCHAR in SQLite?
} {
  <p>Remember, SQLite is typeless.  A VARCHAR column can hold as much
  data as any other column.  The total amount of data in a single row
  of the database is limited to 1 megabyte.  You can increase this limit
  to 16 megabytes, if you need to, by adjusting a single #define in the
  source tree and recompiling.</p>

  <p>For maximum speed and space efficiency, you should try to keep the
  amount of data in a single row below about 230 bytes.</p>
}

faq {
  Does SQLite support a BLOB type?
} {
  <p>You can declare a table column to be of type "BLOB" but it will still
  only store null-terminated strings.  This is because the only way to 
  insert information into an SQLite database is using an INSERT SQL statement,
  and you can not include binary data in the middle of the ASCII text string
  of an INSERT statement.</p>

  <p>SQLite is 8-bit clean with regard to the data is stores as long as
  the data does not contain any NUL characters.  If you want to store binary
  data, consider encoding your data in such a way that it contains no NUL
  characters and inserting it that way.  You might use URL-style encoding:
  encode NUL as "%00" and "%" as "%25".  Or you might consider encoding your
  binary data using base-64.</p>
}

faq {
  How do I add or delete columns from an existing table in SQLite.
} {
  <p>SQLite does not support the "ALTER TABLE" SQL command.  If you
  what to change the structure of a table, you have to recreate the
  table.  You can save existing data to a temporary table, drop the