lang.tcl

sqlite-3.4.1,嵌入式数据库.是一个功能强大的开源数据库,给学习和研发以及小型公司的发展带来了全所未有的好处.

<tr>
<td valign="top" align="right">max(<i>X</i>,<i>Y</i>,...)</td>
<td valign="top">Return the argument with the maximum value.  Arguments
may be strings in addition to numbers.  The maximum value is determined
by the usual sort order.  Note that <b>max()</b> is a simple function when
it has 2 or more arguments but converts to an aggregate function if given
only a single argument.</td>
</tr>

<tr>
<td valign="top" align="right">min(<i>X</i>,<i>Y</i>,...)</td>
<td valign="top">Return the argument with the minimum value.  Arguments
may be strings in addition to numbers.  The minimum value is determined
by the usual sort order.  Note that <b>min()</b> is a simple function when
it has 2 or more arguments but converts to an aggregate function if given
only a single argument.</td>
</tr>

<tr>
<td valign="top" align="right">nullif(<i>X</i>,<i>Y</i>)</td>
<td valign="top">Return the first argument if the arguments are different, 
otherwise return NULL.</td>
</tr>

<tr>
<td valign="top" align="right">quote(<i>X</i>)</td>
<td valign="top">This routine returns a string which is the value of
its argument suitable for inclusion into another SQL statement.
Strings are surrounded by single-quotes with escapes on interior quotes
as needed.  BLOBs are encoded as hexadecimal literals.
The current implementation of VACUUM uses this function.  The function
is also useful when writing triggers to implement undo/redo functionality.
</td>
</tr>

<tr>
<td valign="top" align="right">random(*)</td>
<td valign="top">Return a pseudo-random integer
between -9223372036854775808 and +9223372036854775807.</td>
</tr>

<tr>
<td valign="top" align="right">
<a name="replaceFunc">
replace(<i>X</i>,<i>Y</i>,<i>Z</i>)</td>
<td valign="top">Return a string formed by substituting string <i>Z</i> for
every occurrance of string <i>Y</i> in string <i>X</i>.  The BINARY
collating sequence is used for comparisons.</td>
</tr>

<tr>
<td valign="top" align="right">
<a name="randomblobFunc">
randomblob(<i>N</i>)</td>
<td valign="top">Return a <i>N</i>-byte blob containing pseudo-random bytes.
<i>N</i> should be a postive integer.</td>
</tr>

<tr>
<td valign="top" align="right">round(<i>X</i>)<br>round(<i>X</i>,<i>Y</i>)</td>
<td valign="top">Round off the number <i>X</i> to <i>Y</i> digits to the
right of the decimal point.  If the <i>Y</i> argument is omitted, 0 is 
assumed.</td>
</tr>

<tr>
<td valign="top" align="right">
<a name="rtrimFunc">
rtrim(<i>X</i>)<br>rtrim(<i>X</i>,<i>Y</i>)</td>
<td valign="top">Return a string formed by removing any and all
characters that appear in <i>Y</i> from the right side of <i>X</i>.
If the <i>Y</i> argument is omitted, spaces are removed.</td>
</tr>

<tr>
<td valign="top" align="right">soundex(<i>X</i>)</td>
<td valign="top">Compute the soundex encoding of the string <i>X</i>.
The string "?000" is returned if the argument is NULL.
This function is omitted from SQLite by default.
It is only available the -DSQLITE_SOUNDEX=1 compiler option
is used when SQLite is built.</td>
</tr>

<tr>
<td valign="top" align="right">sqlite_version(*)</td>
<td valign="top">Return the version string for the SQLite library
that is running.  Example:  "2.8.0"</td>
</tr>

<tr>
<td valign="top" align="right">substr(<i>X</i>,<i>Y</i>,<i>Z</i>)</td>
<td valign="top">Return a substring of input string <i>X</i> that begins
with the <i>Y</i>-th character and which is <i>Z</i> characters long.
The left-most character of <i>X</i> is number 1.  If <i>Y</i> is negative
the the first character of the substring is found by counting from the
right rather than the left.  If <i>X</i> is string
then characters indices refer to actual UTF-8 characters.  If
<i>X</i> is a BLOB then the indices refer to bytes.</td>
</tr>

<tr>
<td valign="top" align="right">
<a name="trimFunc">
trim(<i>X</i>)<br>trim(<i>X</i>,<i>Y</i>)</td>
<td valign="top">Return a string formed by removing any and all
characters that appear in <i>Y</i> from both ends of <i>X</i>.
If the <i>Y</i> argument is omitted, spaces are removed.</td>
</tr>


<tr>
<td valign="top" align="right">typeof(<i>X</i>)</td>
<td valign="top">Return the type of the expression <i>X</i>.  The only 
return values are "null", "integer", "real", "text", and "blob".
SQLite's type handling is 
explained in <a href="datatype3.html">Datatypes in SQLite Version 3</a>.</td>
</tr>

<tr>
<td valign="top" align="right">upper(<i>X</i>)</td>
<td valign="top">Return a copy of input string <i>X</i> converted to all
upper-case letters.  The implementation of this function uses the C library
routine <b>toupper()</b> which means it may not work correctly on 
UTF-8 strings.</td>
</tr>

<tr>
<td valign="top" align="right">zeroblob(<i>N</i>)</td>
<td valign="top"><a name="zeroblob">
Return a BLOB consisting of N bytes of 0x00.  SQLite
manages these zeroblobs very efficiently.  Zeroblobs can be used to
reserve space for a BLOB that is later written using 
<a href="capi3ref.html#sqlite3_blob_open">incremental BLOB I/O</a>.</td>
</tr>

</table>

<b>Date And Time Functions</b>

<p>Date and time functions are documented in the 
<a href="http://www.sqlite.org/cvstrac/wiki?p=DateAndTimeFunctions">
SQLite Wiki</a>.</p>

<a name="aggregatefunctions"></a>
<b>Aggregate Functions</b>

<p>
The aggregate functions shown below are available by default.  Additional
aggregate functions written in C may be added using the 
<a href="capi3ref.html#sqlite3_create_function">sqlite3_create_function()</a>
API.</p>

<p>
In any aggregate function that takes a single argument, that argument
can be preceeded by the keyword DISTINCT.  In such cases, duplicate
elements are filtered before being passed into the aggregate function.
For example, the function "count(distinct X)" will return the number
of distinct values of column X instead of the total number of non-null
values in column X.
</p>

<table border=0 cellpadding=10 class="pdf_functions">
<tr>
<td valign="top" align="right" width=120>avg(<i>X</i>)</td>
<td valign="top">Return the average value of all non-NULL <i>X</i> within a
group.  String and BLOB values that do not look like numbers are
interpreted as 0.
The result of avg() is always a floating point value even if all
inputs are integers. </p></td>
</tr>

<tr>
<td valign="top" align="right">count(<i>X</i>)<br>count(*)</td>
<td valign="top">The first form return a count of the number of times
that <i>X</i> is not NULL in a group.  The second form (with no argument)
returns the total number of rows in the group.</td>
</tr>

<tr>
<td valign="top" align="right">max(<i>X</i>)</td>
<td valign="top">Return the maximum value of all values in the group.
The usual sort order is used to determine the maximum.</td>
</tr>

<tr>
<td valign="top" align="right">min(<i>X</i>)</td>
<td valign="top">Return the minimum non-NULL value of all values in the group.
The usual sort order is used to determine the minimum.  NULL is only returned
if all values in the group are NULL.</td>
</tr>

<tr>
<td valign="top" align="right">sum(<i>X</i>)<br>total(<i>X</i>)</td>
<td valign="top">Return the numeric sum of all non-NULL values in the group.
   If there are no non-NULL input rows then sum() returns
   NULL but total() returns 0.0.
   NULL is not normally a helpful result for the sum of no rows
   but the SQL standard requires it and most other
   SQL database engines implement sum() that way so SQLite does it in the
   same way in order to be compatible.   The non-standard total() function
   is provided as a convenient way to work around this design problem
   in the SQL language.</p>

   <p>The result of total() is always a floating point value.
   The result of sum() is an integer value if all non-NULL inputs are integers.
   If any input to sum() is neither an integer or a NULL
   then sum() returns a floating point value
   which might be an approximation to the true sum.</p>

   <p>Sum() will throw an "integer overflow" exception if all inputs
   are integers or NULL
   and an integer overflow occurs at any point during the computation.
   Total() never throws an exception.</p>
</tr>
</table>
}


Section INSERT insert

Syntax {sql-statement} {
INSERT [OR <conflict-algorithm>] INTO [<database-name> .] <table-name> [(<column-list>)] VALUES(<value-list>) |
INSERT [OR <conflict-algorithm>] INTO [<database-name> .] <table-name> [(<column-list>)] <select-statement>
}

puts {
<p>The INSERT statement comes in two basic forms.  The first form
(with the "VALUES" keyword) creates a single new row in an existing table.
If no column-list is specified then the number of values must
be the same as the number of columns in the table.  If a column-list
is specified, then the number of values must match the number of
specified columns.  Columns of the table that do not appear in the
column list are filled with the default value, or with NULL if not
default value is specified.
</p>

<p>The second form of the INSERT statement takes it data from a
SELECT statement.  The number of columns in the result of the
SELECT must exactly match the number of columns in the table if
no column list is specified, or it must match the number of columns
name in the column list.  A new entry is made in the table
for every row of the SELECT result.  The SELECT may be simple
or compound.</p>

<p>The optional conflict-clause allows the specification of an alternative
constraint conflict resolution algorithm to use during this one command.
See the section titled
<a href="#conflict">ON CONFLICT</a> for additional information.
For compatibility with MySQL, the parser allows the use of the
single keyword <a href="#replace">REPLACE</a> as an alias for "INSERT OR REPLACE".
</p>
}


Section {ON CONFLICT clause} conflict

Syntax {conflict-clause} {
ON CONFLICT <conflict-algorithm>
} {conflict-algorithm} {
ROLLBACK | ABORT | FAIL | IGNORE | REPLACE
}

puts {
<p>The ON CONFLICT clause is not a separate SQL command.  It is a
non-standard clause that can appear in many other SQL commands.
It is given its own section in this document because it is not
part of standard SQL and therefore might not be familiar.</p>

<p>The syntax for the ON CONFLICT clause is as shown above for
the CREATE TABLE command.  For the INSERT and
UPDATE commands, the keywords "ON CONFLICT" are replaced by "OR", to make
the syntax seem more natural.  For example, instead of
"INSERT ON CONFLICT IGNORE" we have "INSERT OR IGNORE".
The keywords change but the meaning of the clause is the same
either way.</p>

<p>The ON CONFLICT clause specifies an algorithm used to resolve
constraint conflicts.  There are five choices: ROLLBACK, ABORT,
FAIL, IGNORE, and REPLACE. The default algorithm is ABORT.  This
is what they mean:</p>

<dl>
<dt><b>ROLLBACK</b></dt>
<dd><p>When a constraint violation occurs, an immediate ROLLBACK
occurs, thus ending the current transaction, and the command aborts
with a return code of SQLITE_CONSTRAINT.  If no transaction is
active (other than the implied transaction that is created on every
command) then this algorithm works the same as ABORT.</p></dd>

<dt><b>ABORT</b></dt>
<dd><p>When a constraint violation occurs, the command backs out
any prior changes it might have made and aborts with a return code
of SQLITE_CONSTRAINT.  But no ROLLBACK is executed so changes
from prior commands within the same transaction
are preserved.  This is the default behavior.</p></dd>

<dt><b>FAIL</b></dt>
<dd><p>When a constraint violation occurs, the command aborts with a
return code SQLITE_CONSTRAINT.  But any changes to the database that
the command made prior to encountering the constraint violation
are preserved and are not backed out.  For example, if an UPDATE
statement encountered a constraint violation on the 100th row that
it attempts to update, then the first 99 row changes are preserved
but changes to rows 100 and beyond never occur.</p></dd>

<dt><b>IGNORE</b></dt>
<dd><p>When a constraint violation occurs, the one row that contains
the constraint violation is not inserted or changed.  But the command
continues executing normally.  Other rows before and after the row that
contained the constraint violation continue to be inserted or updated
normally.  No error is returned.</p></dd>

<dt><b>REPLACE</b></dt>
<dd><p>When a UNIQUE constraint violation occurs, the pre-existing rows
that are causing the constraint violation are removed prior to inserting
or updating the current row.  Thus the insert or update always occurs.
The command continues executing normally.  No error is returned.
If a NOT NULL constraint violation occurs, the NULL value is replaced
by the default value for that column.  If the column has no default
value, then the ABORT algorithm is used.  If a CHECK constraint violation
occurs then the IGNORE algorithm is used.</p>

<p>When this conflict resolution strategy deletes rows in order to
satisfy a constraint, it does not invoke delete triggers on those
rows.  This behavior might change in a future release.</p>
</dl>

<p>The algorithm specified in the OR clause of a INSERT or UPDATE
overrides any algorithm specified in a CREATE TABLE.
If no algorithm is specified anywhere, the ABORT algorithm is used.</p>
}

Section REINDEX reindex

Syntax {sql-statement} {
  REINDEX <collation name>
}
Syntax {sql-sta