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New ROWIDs are numbered sequentially. (CVS 383)

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FossilOrigin-Name: 1686196a8aea326f616bc8205df99cd84d955ec4
This commit is contained in:
drh
2002-02-19 22:42:05 +00:00
parent 9562b55115
commit 5cf8e8c7fa
13 changed files with 334 additions and 122 deletions
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www/c_interface.tcl
+2 -2
View File
@@ -1,7 +1,7 @@
#
# Run this Tcl script to generate the sqlite.html file.
#
set rcsid {$Id: c_interface.tcl,v 1.23 2002/01/16 21:00:28 drh Exp $}
set rcsid {$Id: c_interface.tcl,v 1.24 2002/02/19 22:42:06 drh Exp $}
puts {<html>
<head>
@@ -378,7 +378,7 @@ header file that comes in the source tree.</p>
<p>Every row of an SQLite table has a unique integer key. If the
table has a column labeled INTEGER PRIMARY KEY, then that column
servers as the key. If there is no INTEGER PRIMARY KEY column then
the key is a random integer. The key for a row can be accessed in
the key is a unique integer. The key for a row can be accessed in
a SELECT statement or used in a WHERE or ORDER BY clause using any
of the names "ROWID", "OID", or "_ROWID_".</p>
www/changes.tcl
+3
View File
@@ -20,6 +20,9 @@ proc chng {date desc} {
chng {2002 Feb * (2.3.4)} {
<li>Change the name of the sanity_check PRAGMA to <b>integrity_check</b>
and make it available in all compiles.</li>
<li>SELECT min() or max() of an indexed column with no WHERE or GROUP BY
clause is handled as a special case which avoids a complete table scan.</li>
<li>Automatically generated ROWIDs are now sequential.</li>
}
chng {2002 Feb 18 (2.3.3)} {
www/faq.tcl
+31 -52
View File
@@ -1,7 +1,7 @@
#
# Run this script to generated a faq.html output file
#
set rcsid {$Id: faq.tcl,v 1.7 2002/01/22 03:13:43 drh Exp $}
set rcsid {$Id: faq.tcl,v 1.8 2002/02/19 22:42:06 drh Exp $}
puts {<html>
<head>
@@ -27,60 +27,39 @@ proc faq {question answer} {
faq {
How do I create an AUTOINCREMENT field.
} {
SQLite does not support AUTOINCREMENT. If you need a unique key for
a new entry in a table, you can create an auxiliary table
with a single entry that holds the next available value for that key.
Like this:
<p>Short answer: A column declared INTEGER PRIMARY KEY will
autoincrement.</p>
<p>Here is the long answer:
Beginning with version SQLite 2.3.4, 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.
For example, suppose you have a table like this:
<blockquote><pre>
CREATE TABLE counter(cnt);
INSERT INTO counter VALUES(1);
</pre></blockquote>
Once you have a counter set up, you can generate a unique key as follows:
<blockquote><pre>
BEGIN TRANSACTION;
SELECT cnt FROM counter;
UPDATE counter SET cnt=cnt+1;
COMMIT;
</pre></blockquote>
There are other ways of simulating the effect of AUTOINCREMENT but
this approach seems to be the easiest and most efficient.
<p><i>New in SQLite version 2.2.0:</i>
If one of the columns in a table has type INTEGER PRIMARY KEY and
you do an INSERT on that table that does not specify a value for
the primary key, then a unique random number is inserted automatically
in that column. This automatically generated key is random, not
sequential, but you can still use it as a unique identifier.</p>
<p>Here is an example of how the INTEGER PRIMARY KEY feature can be
used:</p>
<blockquote><pre>
CREATE TABLE ex2(
cnum INTEGER PRIMARY KEY,
name TEXT,
email TEXT
CREATE TABLE t1(
a INTEGER PRIMARY KEY,
b INTEGER
);
INSERT INTO ex2(name,email) VALUES('drh','drh@hwaci.com');
INSERT INTO ex2(name,email) VALUES('alle','alle@hwaci.com');
SELECT * FROM ex1;
</pre></blockquote>
<p>Notice that the primary key column <b>cnum</b> is not specified on
the INSERT statements. The output of the SELECT on the last line will
be something like this:</p>
<blockquote>
1597027670|drh|drh@hwaci.com<br>
1597027853|alle|alle@hwaci.com
</blockquote>
<p>The randomly generated keys in this case are 1597027670 and
1597027853. You will probably get different keys every time you
try this. The keys will often be ascending, but this is not always
the case and you cannot count on that behavior. The keys will never
be sequential. If you need sequential keys, use the counter implemention
described first.</p>
<p>With this table, the statement</p>
<blockquote><pre>
INSERT INTO t1 VALUES(NULL,123);
</pre></blockquote>
<p>is logically equivalent to saying:</p>
<blockquote><pre>
INSERT INTO t1 VALUES((SELECT max(a) FROM t1)+1,123);
</pre></blockquote>
<p>For SQLite version 2.2.0 through 2.3.3, if you insert a NULL into
an INTEGER PRIMARY KEY column, the NULL will be changed to a unique
integer, but it will a semi-random integer. Unique keys generated this
way will not be sequential. For SQLite version 2.3.4 and beyond, the
unique keys will be sequential until the largest key reaches a value
of 2147483647. That is the largest 32-bit signed integer and cannot
be incremented, so subsequent insert attempts will revert to the
semi-random key generation algorithm of SQLite version 2.3.3 and
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
www/lang.tcl
+2 -2
View File
@@ -1,7 +1,7 @@
#
# Run this Tcl script to generate the sqlite.html file.
#
set rcsid {$Id: lang.tcl,v 1.25 2002/02/19 13:39:23 drh Exp $}
set rcsid {$Id: lang.tcl,v 1.26 2002/02/19 22:42:06 drh Exp $}
puts {<html>
<head>
@@ -292,7 +292,7 @@ may only hold unique integer values. (Except for this one case,
SQLite ignores the datatype specification of columns and allows
any kind of data to be put in a column regardless of its declared
datatype.) If a table does not have an INTEGER PRIMARY KEY column,
then the B-Tree key will be a randomly generated integer. The
then the B-Tree key will be a automatically generated integer. The
B-Tree key for a row can always be accessed using one of the
special names "<b>ROWID</b>", "<b>OID</b>", or "<b>_ROWID_</b>".
This is true regardless of whether or not there is an INTEGER