#
# Run this Tcl script to generate the vdbe.html file.
#
-set rcsid {$Id: vdbe.tcl,v 1.1 2000/06/23 17:02:18 drh Exp $}
+set rcsid {$Id: vdbe.tcl,v 1.2 2000/06/23 19:16:23 drh Exp $}
puts {<html>
<head>
table that was created like this:</p>
<blockquote><pre>
-CREATE TABLE ex1(col1 text);
+CREATE TABLE ex(one text, two int);
</pre></blockquote>
-<p>In words, we have a database table named "ex1" that has a single
-column of data named "col1". Now suppose we want to insert a single
+<p>In words, we have a database table named "ex" that has two
+columns of data named "one" and "two". Now suppose we want to insert a single
record into this table. Like this:</p>
<blockquote><pre>
-INSERT INTO ex1 VALUES('Hello, World!');
+INSERT INTO ex VALUES('Hello, World!',99);
</pre></blockquote>
<p>We can see the VDBE program that SQLite uses to implement this
Code {
$ (((sqlite test_database_1)))
-sqlite> (((CREATE TABLE ex1(col1 test);)))
+sqlite> (((CREATE TABLE examp(one text, two int);)))
sqlite> (((.explain)))
-sqlite> (((EXPLAIN INSERT INTO ex1 VALUES('Hello, World!');)))
+sqlite> (((EXPLAIN INSERT INTO examp VALUES('Hello, World!',99);)))
addr opcode p1 p2 p3
---- ------------ ----- ----- ----------------------------------------
-0 Open 0 1 ex1
+0 Open 0 1 examp
1 New 0 0
2 String 0 0 Hello, World!
-3 MakeRecord 1 0
-4 Put 0 0
+3 Integer 99 0
+4 MakeRecord 2 0
+5 Put 0 0
}
puts {<p>As you can see above, our simple insert statement is
-implemented in just 5 instructions. There are no jumps, so the
+implemented in just 6 instructions. There are no jumps, so the
program executes once through from top to bottom. Let's now
look at each instruction in detail.</p>
<p>The first instruction opens a cursor that points into the
-"ex1" table. The P1 operand is a handle for the cursor: zero
+"examp" table. The P1 operand is a handle for the cursor: zero
in this case. Cursor handles can be any non-negative integer.
But the VDBE allocates cursors in an array with the size of the
array being one more than the largest cursor. So to conserve
another cursor open for writing that same file.</p>
<p>The second instruction, New, generates an integer key that
-has not been previously used in the file "ex1". The New instruction
+has not been previously used in the file "examp". The New instruction
uses its P1 operand as the handle of a cursor for the file
for which the new key will be generated. The new key is
pushed onto the stack. The P2 and P3 operands are not used
stack {The string "Hello, World!"} {A random integer key}
-puts {<p>The 4th instructionn, MakeRecord, pops the top P1
-elements off the stack (1 element in this case) and converts them
+puts {<p>The 4th instruction pushes an integer value 99 onto the
+stack. After the 4th instruction executes, the stack looks like this:</p>
+}
+
+stack {Integer value 99} {The string "Hello, World!"} {A random integer key}
+
+
+puts {<p>The 5th instructionn, MakeRecord, pops the top P1
+elements off the stack (2 elements in this case) and converts them
all into the binary format used for storing records in a
database file. (See the <a href="fileformat.html">file format</a>
description for details.) The record format consists of
Following the header is the data for each column, Each column
is stored as a null-terminated ASCII text string. The new
record generated by the MakeRecord instruction is pushed back
-onto the stack, so that after the 4th instruction executes,
+onto the stack, so that after the 5th instruction executes,
the stack looks like this:</p>
}
-stack {A one-column record containing "Hello, World!"} \
+stack {A data record holding "Hello, World!" and 99} \
{A random integer key}
puts {<p>The last instruction pops top elements from the stack
all open cursors, frees any elements left on the stack,
and releases any other resources we may have allocated.
In this case, the only cleanup necessary is to close the
-open cursor to the "ex1" file.</p>
+open cursor to the "examp" file.</p>
<a name="trace">
<h2>Tracing VDBE Program Execution</h2>
Code {
sqlite> (((--vdbe-trace-on--)))
- ...> (((INSERT INTO ex1 VALUES('Hello, World!');)))
- 0 Open 0 1 ex1
+ ...> (((INSERT INTO examp VALUES('Hello, World!',99);)))
+ 0 Open 0 1 examp
1 New 0 0
-Stack: i:179007474
+Stack: i:1053779177
2 String 0 0 Hello, World!
-Stack: s:[Hello, Worl] i:179007474
- 3 MakeRecord 1 0
-Stack: z:[] i:179007474
- 4 Put 0 0
+Stack: s:[Hello, Worl] i:1053779177
+ 3 Integer 99 0
+Stack: i:99 s:[Hello, Worl] i:1053779177
+ 4 MakeRecord 2 0
+Stack: z:] i:1053779177
+ 5 Put 0 0
}
puts {
We will use the follow simple SELECT statement as our example:</p>
<blockquote><pre>
-SELECT col1 FROM ex1;
+SELECT * FROM examp;
</pre></blockquote>
<p>The VDBE program generated for this SQL statement is as follows:</p>
}
Code {
-sqlite> (((EXPLAIN SELECT * FROM ex1;)))
-addr opcode p1 p2 p3
----- ------------ ----- ----- ----------------------------------------
-0 ColumnCount 1 0
-1 ColumnName 0 0 col1
-2 Open 0 0 ex1
-3 Next 0 7
-4 Field 0 0
-5 Callback 1 0
-6 Goto 0 3
-7 Close 0 0
+sqlite> (((EXPLAIN SELECT * FROM examp;)))
+0 ColumnCount 2 0
+1 ColumnName 0 0 one
+2 ColumnName 1 0 two
+3 Open 0 0 examp
+4 Next 0 9
+5 Field 0 0
+6 Field 0 1
+7 Callback 2 0
+8 Goto 0 4
+9 Close 0 0
}
puts {
of one of the result column. <b>azData[]</b> is an array of strings holding
the actual data.</p>
-<p>The first two instructions in the VDBE program for our query are
-considered with setting up values for <b>azColumn</b>.
+<p>The first three instructions in the VDBE program for our query are
+concerned with setting up values for <b>azColumn</b>.
The ColumnCount instruction tells the VDBE how much space to allocate
for the <b>azColumnName[]</b> array. The ColumnName instructions
-tell the VDBE what value to fill in for each element of the
-<b>azColumnName[]</b> array. Every query will begin with once
-ColumnCount instruction and once ColumnName instruction for each
+tell the VDBE what values to fill in for each element of the
+<b>azColumnName[]</b> array. Every query will begin with one
+ColumnCount instruction and one ColumnName instruction for each
column in the result.</p>
-<p>The third instruction opens a cursor into the database file
+<p>The 4th instruction opens a cursor into the database file
that is to be queried. This works the same as the Open instruction
-in the INSERT example <a href="#insert1">above</a> except that the
+in the INSERT example except that the
cursor is opened for reading this time instead of for writing.</p>
-<p>The instructions at address 3 and 6 form a loop that will execute
+<p>The instructions at address 4 and 8 form a loop that will execute
once for each record in the database file. This is a key concept that
you should pay close attention to. The Next instruction at
-address 3 tell the VDBE to advance the cursor (identified by P1)
-to the next record. The first time Next instruction is executed,
+address 4 tells the VDBE to advance the cursor (identified by P1)
+to the next record. The first time this Next instruction is executed,
the cursor is set to the first record of the file. If there are
no more records in the database file when Next is executed, then
the VDBE makes an immediate jump over the body of the loop to
-instruction 7 (specified by operand P2). The body of the loop
-is formed by instructions at addresses 4 and 5. After the loop
-body is an unconditional jump at instruction 6 which takes us
+instruction 9 (specified by operand P2). The body of the loop
+is formed by instructions at addresses 5, 6, and 7. After the loop
+body is an unconditional jump at instruction 8 which takes us
back to the Next instruction at the beginning of the loop.
</p>
-<p>The body of the loop consists of instructions at addresses 4 and
-5. The Field instruction at address 4 takes the P2-th column from
+<p>The body of the loop consists of instructions at addresses 5 through
+7. The Field instructions at addresses 5 and 6 each
+take the P2-th column from
the P1-th cursor and pushes it onto the stack.
(The "Field" instruction probably should be renamed as the "Column"
-instruction.) In this example, the Field instruction is pushing the
-value for the "col1" data column onto the stack.</p>
+instruction.) In this example, the first Field instruction is pushing the
+value for the "one" data column onto the stack and the second Field
+instruction is pushing the data for "two".</p>
-<p>The Callback instruction at address 5 invokes the callback function.
+<p>The Callback instruction at address 7 invokes the callback function.
The P1 operand to callback becomes the value for <b>nColumn</b>.
The Callback instruction also pops P1 values from the stack and
uses them to form the <b>azData[]</b> for the callback.</p>
<p>The Close instruction at the end of the program closes the
cursor that points into the database file. It is not really necessary
-to call close here since all cursors will be automatically closed
+to call Close here since all cursors will be automatically closed
by the VDBE when the program halts. But we needed an instruction
for the Next to jump to so we might as well go ahead and have that
instruction do something useful.</p>
instruction to invoke the callback function, and the use of the Next
instruction to implement a loop over all records of the database file.
This example attempts to drive home those ideas by demonstrating a
-slightly more complex query that involves multiple columns of
+slightly more complex query that involves more columns of
output, some of which are computed values, and a WHERE clause that
limits which records actually make it to the callback function.
Consider this query:</p>
<blockquote><pre>
-SELECT col1 AS 'Name', '**' || col1 || '**' AS 'With Stars'
-FROM ex1
-WHERE col1 LIKE '%ll%'
+SELECT one, two, one || two AS 'both'
+FROM examp
+WHERE one LIKE 'H%'
</pre></blockquote>
<p>This query is perhaps a bit contrived, but it does serve to
-illustrate our points. The result will have two column with
-names "Name" and "With Stars". The first column is just the
-sole column in our simple example table. The second column
-of the result is the same as the first column except that
-asterisks have been prepended and appended. Finally, the
+illustrate our points. The result will have three column with
+names "one", "two", and "both". The first two columns are direct
+copies of the two columns in the table and the third result
+column is a string formed by concatenating the first and
+second columns of the table.
+Finally, the
WHERE clause says that we will only chose rows for the
-results that contain two "l" characters in a row. Here is
-what the VDBE program looks like for this query:</p>
+results where the "one" column begins with an "H".
+Here is what the VDBE program looks like for this query:</p>
}
Code {
-sqlite> (((EXPLAIN SELECT col1 AS 'Name', '**' || col1 || '**' AS 'With Stars')))
- ...> (((FROM ex1)))
- ...> (((WHERE col1 LIKE '%ll%';)))
addr opcode p1 p2 p3
---- ------------ ----- ----- ----------------------------------------
-0 ColumnCount 2 0
-1 ColumnName 0 0 Name
-2 ColumnName 1 0 With Stars
-3 Open 0 0 ex1
-4 Next 0 16
-5 Field 0 0
-6 String 0 0 %ll%
-7 Like 1 4
-8 Field 0 0
-9 String 0 0 **
-10 Field 0 0
-11 Concat 2 0
-12 String 0 0 **
+0 ColumnCount 3 0
+1 ColumnName 0 0 one
+2 ColumnName 1 0 two
+3 ColumnName 2 0 both
+4 Open 0 0 examp
+5 Next 0 16
+6 Field 0 0
+7 String 0 0 H%
+8 Like 1 5
+9 Field 0 0
+10 Field 0 1
+11 Field 0 0
+12 Field 0 1
13 Concat 2 0
-14 Callback 2 0
-15 Goto 0 4
+14 Callback 3 0
+15 Goto 0 5
16 Close 0 0
}
puts {
<p>Except for the WHERE clause, the structure of the program for
this example is very much like the prior example, just with an
-extra column. The ColumnCount is 2 now, instead of 1 as before,
-and there are two ColumnName instructions.
+extra column. The ColumnCount is 3 now, instead of 2 as before,
+and there are three ColumnName instructions.
A cursor is opened using the Open instruction, just like in the
-prior example. The Next instruction at address 4 and the
+prior example. The Next instruction at address 5 and the
Goto at address 15 form a loop over all records of the database
file. The Close instruction at the end is there to give the
Next instruction something to jump to when it is done. All of
this is just like in the first query demonstration.</p>
<p>The Callback instruction in this example has to generate
-data for two result columns instead of one, but is otherwise
+data for three result columns instead of two, but is otherwise
the same as in the first query. When the Callback instruction
is invoked, the left-most column of the result should be
the lowest in the stack and the right-most result column should
be the top of the stack. We can see the stack being set up
-this way at addresses 8 through 13. The Field instruction at
-8 pushes the value of the "col1" column of table "ex1" onto the
-stack, and that is all that has to be done for the left column
-of the result. Instructions at 9 through 13 evaluate the
-expression used for the second result column and leave it
-on the stack as well.</p>
+this way at addresses 9 through 13. The Field instructions at
+9 and 10 push the values for the first two columns in the result.
+The two Field instructions at 11 and 12 pull in the values needed
+to compute the third result column and the Concat instruction at
+13 joins them together into a single entry on the stack.</p>
<p>The only thing that is really new about the current example
is the WHERE clause which is implemented by instructions at
-addresses 5, 6, and 7. Instructions at address 5 and 6 push
-onto the stack the value of the "col1" column and the literal
-string "%ll%". The Like instruction at address 7 pops these
+addresses 6, 7, and 8. Instructions at address 6 and 7 push
+onto the stack the value of the "one" column from the table
+and the literal string "H%". The Like instruction at address 8 pops these
two values from the stack and causes an
-immediate jump back to the Next instruction if the "col1" value
-is <em>not</em> like the literal string "%ll%". Taking this
+immediate jump back to the Next instruction if the "one" value
+is <em>not</em> like the literal string "H%". Taking this
jump effectively skips the callback, which is the whole point
of the WHERE clause. If the result
of the comparison is true, the jump is not taken and control
comparison fails. So with P1 equal to one, a more precise
name for this instruction might be "Jump If NOS Is Not Like TOS".
The sense of the test in inverted if P1 is 0. So when P1
-is zero, the instruction is more like "Jump If NOS Is Like TOS".
+is zero, the instruction is "Jump If NOS Is Like TOS".
</p>
<a name="pattern1">
by looking at a DELETE statement:</p>
<blockquote><pre>
-DELETE FROM ex1 WHERE col1 NOT LIKE '%H%'
+DELETE FROM examp WHERE two<50;
</pre></blockquote>
-<p>This DELETE statement will remove every record from the "ex1"
-table that does not contain an "H" characters in the "col1"
-column. The code generated to do this is as follows:</p>
+<p>This DELETE statement will remove every record from the "examp"
+table where the "two" column is less than 50.
+The code generated to do this is as follows:</p>
}
Code {
-sqlite> (((EXPLAIN DELETE FROM ex1 WHERE col1 NOT LIKE '%H%';)))
addr opcode p1 p2 p3
---- ------------ ----- ----- ----------------------------------------
0 ListOpen 0 0
-1 Open 0 0 ex1
+1 Open 0 0 examp
2 Next 0 9
-3 Field 0 0
-4 String 0 0 %H%
-5 Like 0 2
+3 Field 0 1
+4 Integer 50 0
+5 Ge 0 2
6 Key 0 0
7 ListWrite 0 0
8 Goto 0 2
9 Close 0 0
10 ListRewind 0 0
-11 Open 0 1 ex1
+11 Open 0 1 examp
12 ListRead 0 15
13 Delete 0 0
14 Goto 0 12
puts {
<p>Here is what the program must do. First it has to locate all of
-the records in the "ex1" database that are to be deleted. This is
+the records in the "examp" database that are to be deleted. This is
done using a loop very much like the loop used in the SELECT examples
above. Once all records have been located, then we can go back through
an delete them one by one. Note that we cannot delete each record
as soon as we find it. We have to locate all records first, then
-go back and delete them. This is because with the GDBM database
-backend (as with most other backends based on hashing) when you
-delete a record it might change the scan order. And if the scan
+go back and delete them. This is because the GDBM database
+backend might change the scan order after a delete operation.
+And if the scan
order changes in the middle of the scan, some records might be
tested more than once, and some records might not be tested at all.</p>
<p>So the implemention of DELETE is really in two loops. The
-first loop (instructions 3 through 8 in the example) locates the records that
+first loop (instructions 2 through 8 in the example) locates the records that
are to be deleted and the second loop (instructions 12 through 14)
do the actual deleting.</p>
handles. As currently implemented, SQLite never uses more than one
list at a time and so it always uses the handle of 0 for every list.</p>
-<p>Each list is really a file descriptor for a temporary file that
-is created for holding the list. What's going to happen is this: the
-first loop of the program is going to locate records that need to
+<p>Lists are implemented using temporary files.
+The program will work like this:
+the first loop will locate records that need to
be deleted and write their keys onto the list. Then the second
-loop is going to playback the list and delete the records one by one.</p>
+loop will playback the list and delete the records one by one.</p>
-<p>The second instruction opens a cursor to the database file "ex1".
+<p>The second instruction opens a cursor to the database file "examp".
Notice that the cursor is opened for reading, not writing. At this
stage of the program we are going to be scanning the file not changing
it. We will reopen the same file for writing it later, at instruction 11.
by P1. The integer is a key to a record that should be deleted and
was placed on the stack by the preceding Key instruction.
The WHERE clause is implemented by instructions 3, 4, and 5.
-The implementation of the WHERE clause is exactly the same as in the
-previous SELECT statement, except that the P1 operand to the Like
-instruction is 0 instead of one because the DELETE statement uses
-the NOT LIKE operator instead of the LIKE operator. If the WHERE
-clause evaluates to false (if col2 is like "%ll%") then the ListWrite
-instruction gets skipped and the key to that record is never written
-to the list. Hence, the record is not deleted.</p>
+The job of the where clause is to skip the ListWrite if the WHERE
+condition is false. To this end, it jumps back to the Next instruction
+if the "two" column (extracted by the Field instruction at 3) is
+greater than or equal to 50.</p>
<p>At the end of the first loop, the cursor is closed at instruction 9,
and the list is rewound back to the beginning at instruction 10.
-Next, instruction 11 reopens the same database file, but for
+The Open instruction at 11 reopens the same database file, but for
writing this time. The loop that does the actual deleting of records
is on instructions 12, 13, and 14.</p>
<p>The ListRead instruction as 12 reads a single integer key from
the list and pushes that key onto the stack. If there are no
more keys, nothing gets pushed onto the stack but instead a jump
-is made to instruction 15. Notice the similarity of operation
+is made to instruction 15. Notice the similarity
between the ListRead and Next instructions. Both operations work
-something like this:</p>
+according to this rule:</p>
<blockquote>
Push the next "thing" onto the stack and fall through.
Or if there is no next "thing" to push, jump immediately to P2.
</blockquote>
-<p>The only difference between Next and ListRead is the definition
-of "next thing". The "things" for the Next instruction are records
+<p>The only difference between Next and ListRead is their idea
+of a "thing". The "things" for the Next instruction are records
in a database file. "Things" for ListRead are integer keys in a list.
Later on,
we will see other looping instructions (NextIdx and SortNext) that
<p>The Delete instruction at address 13 pops an integer key from
the stack (the key was put there by the preceding ListRead
instruction) and deletes the record of cursor P1 that has that key.
-If there is not record in the database with the given key, then
+If there is no record in the database with the given key, then
Delete is a no-op.</p>
<p>There is a Goto instruction at 14 to complete the second loop.
Then at instruction 15 is as ListClose operation. The ListClose
-closes the list and deletes the temporary that held the ist.
+closes the list and deletes the temporary file that held it.
Calling ListClose is optional. The VDBE will automatically close
the list when it halts. But we need an instruction for the
ListRead to jump to when it reaches the end of the list and
</p>
<blockquote><pre>
-UPDATE ex1 SET col1='H' || col1 WHERE col1 NOT LIKE '%H%'
+UPDATE examp SET one= '(' || one || ')' WHERE two < 50;
</pre></blockquote>
-<p>Instead of deleting records that lack an "H" in column "col1",
-this statement changes the column by prepending an "H".
+<p>Instead of deleting records where the "two" column is less than
+50, this statement just puts the "one" column in paraentheses
The VDBE program to implement this statement follows:</p>
}
addr opcode p1 p2 p3
---- ------------ ----- ----- ----------------------------------------
0 ListOpen 0 0
-1 Open 0 0 ex1
+1 Open 0 0 examp
2 Next 0 9
-3 Field 0 0
-4 String 0 0 %H%
-5 Like 0 2
+3 Field 0 1
+4 Integer 50 0
+5 Ge 0 2
6 Key 0 0
7 ListWrite 0 0
8 Goto 0 2
9 Close 0 0
10 ListRewind 0 0
-11 Open 0 1 ex1
-12 ListRead 0 21
+11 Open 0 1 examp
+12 ListRead 0 24
13 Dup 0 0
14 Fetch 0 0
-15 String 0 0 H
+15 String 0 0 (
16 Field 0 0
17 Concat 2 0
-18 MakeRecord 1 0
-19 Put 0 0
-20 Goto 0 12
-21 ListClose 0 0
+18 String 0 0 )
+19 Concat 2 0
+20 Field 0 1
+21 MakeRecord 2 0
+22 Put 0 0
+23 Goto 0 12
+24 ListClose 0 0
}
puts {
<p>This program is exactly the same as the DELETE program
except that the single Delete instruction in the second loop
has been replace by a sequence of instructions (at addresses
-13 through 19) that update the record rather than delete it.
-Most of this instruction sequence you already be familiar to
+13 through 22) that update the record rather than delete it.
+Most of this instruction sequence should already be familiar to
you, but there are a couple of minor twists so we will go
over it briefly.</p>
<p>As we enter the interior of the second loop (at instruction 13)
the stack contains a single integer which is the key of the
record we want to modify. We are going to need to use this
-key twice: once to fetch the old value of column "col1" and
-a second time to write back the new value. So the first instruction
-is a Dup to make a duplicate of the top of the stack. The
-VDBE Dup instruction is actually a little more general than that.
-It will duplicate any element of the stack, not just the top
+key twice: once to fetch the old value of the record and
+a second time to write back the revised record. So the first instruction
+is a Dup to make a duplicate of the key on the top of the stack. The
+Dup instruction will duplicate any element of the stack, not just the top
element. You specify which element to duplication using the
P1 operand. When P1 is 0, the top of the stack is duplicated.
When P1 is 1, the next element down on the stack duplication.
And so forth.</p>
-<p>After duplicating the key, the next instruction is Fetch
+<p>After duplicating the key, the next instruction, Fetch,
pops the stack once and uses the value popped as a key to
load a record from the database file. In this way, we obtain
the old column values for the record that is about to be
updated.</p>
-<p>Instructions 15 through 18 construct a new database record
+<p>Instructions 15 through 21 construct a new database record
that will be used to replace the existing record. This is
-the same kind of code that we say <a href="#insert1">above</a>
+the same kind of code that we saw
in the description of INSERT and will not be described further.
-After instruction 18 executes, the stack looks like this:</p>
+After instruction 21 executes, the stack looks like this:</p>
}
stack {New data record} {Integer key}
puts {
-<p>The Put instruction (also described <a href="#insert1">above</a>
+<p>The Put instruction (also described
during the discussion about INSERT) writes an entry into the
database file whose data is the top of the stack and whose key
is the next on the stack, and then pops the stack twice. The
Put instruction will overwrite the data of an existing record
-with the same key, which is what we want here. It was not
+with the same key, which is what we want here. Overwriting was not
an issue with INSERT because with INSERT the key was generated
-by the Key instruction which is guaranteed to generate a key
-that has not been used before. (By the way, since keys must
+by the Key instruction which is guaranteed to provide a key
+that has not been used before.</p>
+}
+
+if 0 {(By the way, since keys must
all be unique and each key is a 32-bit integer, a single
SQLite database table can have no more than 2<sup>32</sup>
rows. Actually, the Key instruction starts to become
is best to keep the number of entries below 2<sup>31</sup>
or so. Surely a couple billion records will be enough for
most applications!)</p>
+}
+
+puts {
+<h2>CREATE and DROP</h2>
+
+<p>Using CREATE or DROP to create or destroy a table or index is
+really the same as doing an INSERT or DELETE from the special
+"sqlite_master" table, at least from the point of view of the VDBE.
+The sqlite_master table is a special table that is automatically
+created for every SQLite database. It looks like this:</p>
+
+<blockquote><pre>
+CREATE TABLE sqlite_master (
+ type TEXT, -- either "table" or "index"
+ name TEXT, -- name of the table or index
+ tbl_name TEXT, -- for indices: name of associated table
+ sql TEXT -- SQL text of the original CREATE statement
+)
+</pre></blockquote>
-<p>The rest of the UPDATE program is the same as for DELETE,
-and for all the same reasons.</p>
+<p>Every table (except the "sqlite_master" table itself)
+and every named index in an SQLite database has an entry
+in the sqlite_master table. You can query this table using
+a SELECT statement just like any other table. But you are
+not allowed to directly change the table using UPDATE, INSERT,
+or DELETE. Changes to sqlite_master have to occur using
+the CREATE and DROP commands because SQLite also has to update
+some of its internal data structures when tables and indices
+are added or destroyed.</p>
+
+<p>But from the point of view of the VDBE, a CREATE works
+pretty much like an INSERT and a DROP works like a DELETE.
+When the SQLite library opens to an existing database,
+the first thing it does is a SELECT to read the "sql"
+columns from all entries of the sqlite_master table.
+The "sql" column contains the complete SQL text of the
+CREATE statement that originally generated the index or
+table. This text is fed back into the SQLite parse
+and used to reconstruct the
+internal data structures describing the index or table.</p>
+
+<h2>Using Indexes To Speed Searches</h2>
+<i>TBD</i>
+<h2>Joins</h2>
+<i>TBD</i>
+<h2>The ORDER BY clause</h2>
+<i>TBD</i>
+<h2>Aggregate Functions And The GROUP BY and HAVING Clauses</h2>
+<i>TBD</i>
+<h2>Using SELECT Statements As Terms In An Expression</h2>
+<i>TBD</i>
+<h2>Compound SELECT Statements</h2>
+<i>TBD</i>
}
puts {
projects / thirdparty / sqlite.git / commitdiff
