lang.tcl

一个小型的嵌入式数据库

 ROLLBACK) and the current query terminates. An error code of SQLITE_CONSTRAINT is returned to the user, along with the specified error message.</p>

<p>When RAISE(IGNORE) is called, the remainder of the current trigger program,
the statement that caused the trigger program to execute and any subsequent
    trigger programs that would of been executed are abandoned. No database
    changes are rolled back.  If the statement that caused the trigger program
    to execute is itself part of a trigger program, then that trigger program
    resumes execution at the beginning of the next step.
</p>

<p>Triggers are removed using the <a href="#droptrigger">DROP TRIGGER</a>
statement.  Non-temporary triggers cannot be added on a table in an 
attached database.</p>
}


Section {CREATE VIEW} {createview}

Syntax {sql-command} {
CREATE [TEMP | TEMPORARY] VIEW [<database-name>.] <view-name> AS <select-statement>
}

puts {
<p>The CREATE VIEW command assigns a name to a pre-packaged 
<a href="#select">SELECT</a>
statement.  Once the view is created, it can be used in the FROM clause
of another SELECT in place of a table name.
</p>

<p>If the "TEMP" or "TEMPORARY" keyword occurs in between "CREATE"
and "TABLE" then the table that is created is only visible to the
process that opened the database and is automatically deleted when
the database is closed.</p>

<p> If a <database-name> is specified, then the view is created in 
the named database. It is an error to specify both a <database-name>
and the TEMP keyword, unless the <database-name> is "temp". If no
database name is specified, and the TEMP keyword is not present,
the table is created in the main database.</p>

<p>You cannot COPY, DELETE, INSERT or UPDATE a view.  Views are read-only 
in SQLite.  However, in many cases you can use a <a href="#createtrigger">
TRIGGER</a> on the view to accomplish the same thing.  Views are removed 
with the <a href="#dropview">DROP VIEW</a> 
command.  Non-temporary views cannot be created on tables in an attached 
database.</p>
}


Section DELETE delete

Syntax {sql-statement} {
DELETE FROM [<database-name> .] <table-name> [WHERE <expr>]
}

puts {
<p>The DELETE command is used to remove records from a table.
The command consists of the "DELETE FROM" keywords followed by
the name of the table from which records are to be removed.
</p>

<p>Without a WHERE clause, all rows of the table are removed.
If a WHERE clause is supplied, then only those rows that match
the expression are removed.</p>
}


Section {DETACH DATABASE} detach

Syntax {sql-command} {
DETACH [DATABASE] <database-name>
}

puts {
<p>This statement detaches an additional database connection previously 
attached using the <a href="#attach">ATTACH DATABASE</a> statement.  It
is possible to have the same database file attached multiple times using 
different names, and detaching one connection to a file will leave the 
others intact.</p>

<p>This statement will fail if SQLite is in the middle of a transaction.</p>
}


Section {DROP INDEX} dropindex

Syntax {sql-command} {
DROP INDEX [<database-name> .] <index-name>
}

puts {
<p>The DROP INDEX statement removes an index added
with the <a href="#createindex">
CREATE INDEX</a> statement.  The index named is completely removed from
the disk.  The only way to recover the index is to reenter the
appropriate CREATE INDEX command.</p>

<p>The DROP INDEX statement does not reduce the size of the database 
file.  Empty space in the database is retained for later INSERTs.  To 
remove free space in the database, use the <a href="#vacuum">VACUUM</a> 
command.</p>
}


Section {DROP TABLE} droptable

Syntax {sql-command} {
DROP TABLE [<database-name>.] <table-name>
}

puts {
<p>The DROP TABLE statement removes a table added with the <a href=
"#createtable">CREATE TABLE</a> statement.  The name specified is the
table name.  It is completely removed from the database schema and the 
disk file.  The table can not be recovered.  All indices associated 
with the table are also deleted.  Non-temporary tables in an attached 
database cannot be dropped.</p>

<p>The DROP TABLE statement does not reduce the size of the database 
file.  Empty space in the database is retained for later INSERTs.  To 
remove free space in the database, use the <a href="#vacuum">VACUUM</a> 
command.</p>
}


Section {DROP TRIGGER} droptrigger
Syntax {sql-statement} {
DROP TRIGGER [<database-name> .] <trigger-name>
}
puts { 
<p>The DROP TRIGGER statement removes a trigger created by the 
<a href="#createtrigger">CREATE TRIGGER</a> statement.  The trigger is 
deleted from the database schema. Note that triggers are automatically 
dropped when the associated table is dropped.  Non-temporary triggers 
cannot be dropped on attached tables.</p>
}


Section {DROP VIEW} dropview

Syntax {sql-command} {
DROP VIEW <view-name>
}

puts {
<p>The DROP VIEW statement removes a view created by the <a href=
"#createview">CREATE VIEW</a> statement.  The name specified is the 
view name.  It is removed from the database schema, but no actual data 
in the underlying base tables is modified.  Non-temporary views in 
attached databases cannot be dropped.</p>
}


Section EXPLAIN explain

Syntax {sql-statement} {
EXPLAIN <sql-statement>
}

puts {
<p>The EXPLAIN command modifier is a non-standard extension.  The
idea comes from a similar command found in PostgreSQL, but the operation
is completely different.</p>

<p>If the EXPLAIN keyword appears before any other SQLite SQL command
then instead of actually executing the command, the SQLite library will
report back the sequence of virtual machine instructions it would have
used to execute the command had the EXPLAIN keyword not been present.
For additional information about virtual machine instructions see
the <a href="arch.html">architecture description</a> or the documentation
on <a href="opcode.html">available opcodes</a> for the virtual machine.</p>
}


Section expression expr

Syntax {expr} {
<expr> <binary-op> <expr> |
<expr> <like-op> <expr> [ESCAPE <expr>] |
<expr> <glob-op> <expr> |
<unary-op> <expr> |
( <expr> ) |
<column-name> |
<table-name> . <column-name> |
<database-name> . <table-name> . <column-name> |
<literal-value> |
<function-name> ( <expr-list> | STAR ) |
<expr> ISNULL |
<expr> NOTNULL |
<expr> [NOT] BETWEEN <expr> AND <expr> |
<expr> [NOT] IN ( <value-list> ) |
<expr> [NOT] IN ( <select-statement> ) |
<expr> [NOT] IN [<database-name> .] <table-name> |
[EXISTS] ( <select-statement> ) |
CASE [<expr>] LP WHEN <expr> THEN <expr> RPPLUS [ELSE <expr>] END
} {like-op} {
LIKE | NOT LIKE
} {glob-op} {
GLOB | NOT GLOB
}

puts {
<p>This section is different from the others.  Most other sections of
this document talks about a particular SQL command.  This section does
not talk about a standalone command but about "expressions" which are 
subcomponents of most other commands.</p>

<p>SQLite understands the following binary operators, in order from
highest to lowest precedence:</p>

<blockquote><pre>
<font color="#2c2cf0"><big>||
*    /    %
+    -
&lt;&lt;   &gt;&gt;   &amp;    |
&lt;    &lt;=   &gt;    &gt;=
=    ==   !=   &lt;&gt;   </big>IN
AND   
OR</font>
</pre></blockquote>

<p>Supported unary operators are these:</p>

<blockquote><pre>
<font color="#2c2cf0"><big>-    +    !    ~</big></font>
</pre></blockquote>

<p>Any SQLite value can be used as part of an expression.  
For arithmetic operations, integers are treated as integers.
Strings are first converted to real numbers using <b>atof()</b>.
For comparison operators, numbers compare as numbers and strings
compare using the <b>strcmp()</b> function.
Note that there are two variations of the equals and not equals
operators.  Equals can be either}
puts "[Operator =] or [Operator ==].
The non-equals operator can be either
[Operator !=] or [Operator {&lt;&gt;}].
The [Operator ||] operator is \"concatenate\" - it joins together
the two strings of its operands.
The operator [Operator %] outputs the remainder of its left 
operand modulo its right operand.</p>"
puts {

<a name="like"></a>
<p>The LIKE operator does a pattern matching comparison. The operand
to the right contains the pattern, the left hand operand contains the
string to match against the pattern. 
}
puts "A percent symbol [Operator %] in the pattern matches any
sequence of zero or more characters in the string.  An underscore
[Operator _] in the pattern matches any single character in the
string.  Any other character matches itself or it's lower/upper case
equivalent (i.e. case-insensitive matching).  (A bug: SQLite only
understands upper/lower case for 7-bit Latin characters.  Hence the
LIKE operator is case sensitive for 8-bit iso8859 characters or UTF-8
characters.  For example, the expression <b>'a'&nbsp;LIKE&nbsp;'A'</b>
is TRUE but <b>'&aelig;'&nbsp;LIKE&nbsp;'&AElig;'</b> is FALSE.).</p>"

puts {
<p>If the optional ESCAPE clause is present, then the expression
following the ESCAPE keyword must evaluate to a string consisting of
a single character. This character may be used in the LIKE pattern
to include literal percent or underscore characters. The escape
character followed by a percent symbol, underscore or itself matches a
literal percent symbol, underscore or escape character in the string,
respectively. The infix LIKE operator is implemented by calling the
user function <a href="#likeFunc"> like(<i>X</i>,<i>Y</i>)</a>.</p>
}

puts {
<p>The LIKE operator does a wildcard comparison.  The operand
to the right contains the wildcards.}
puts "A percent symbol [Operator %] in the right operand
matches any sequence of zero or more characters on the left.
An underscore [Operator _] on the right
matches any single character on the left."

puts {
The LIKE operator is not case sensitive and will match upper case
characters on one side against lower case characters on the other.  
(A bug: SQLite only understands upper/lower case for 7-bit Latin
characters.  Hence the LIKE operator is case sensitive for 8-bit
iso8859 characters or UTF-8 characters.  For example, the expression
<b>'a'&nbsp;LIKE&nbsp;'A'</b> is TRUE but
<b>'&aelig;'&nbsp;LIKE&nbsp;'&AElig;'</b> is FALSE.).  The infix LIKE
operator is identical the user function <a href="#likeFunc">
like(<i>X</i>,<i>Y</i>)</a>.
</p>

<a name="glob"></a>
<p>The GLOB operator is similar to LIKE but uses the Unix
file globbing syntax for its wildcards.  Also, GLOB is case
sensitive, unlike LIKE.  Both GLOB and LIKE may be preceded by
the NOT keyword to invert the sense of the test.  The infix GLOB 
operator is identical the user function <a href="#globFunc">
glob(<i>X</i>,<i>Y</i>)</a>.</p>

<p>A column name can be any of the names defined in the CREATE TABLE
statement or one of the following special identifiers: "<b>ROWID</b>",
"<b>OID</b>", or "<b>_ROWID_</b>".
These special identifiers all describe the
unique random integer key (the "row key") associated with every 
row of every table.
The special identifiers only refer to the row key if the CREATE TABLE
statement does not define a real column with the same name.  Row keys
act like read-only columns.  A row key can be used anywhere a regular
column can be used, except that you cannot change the value
of a row key in an UPDATE or INSERT statement.
"SELECT * ..." does not return the row key.</p>

<p>SELECT statements can appear in expressions as either the
right-hand operand of the IN operator, as a scalar quantity, or
as the operand of an EXISTS operator.
As a scalar quantity or the operand of an IN operator,
the SELECT should have only a single column in its
result.  Compound SELECTs (connected with keywords like UNION or
EXCEPT) are allowed.
With the EXISTS operator, the columns in the result set of the SELECT are
ignored and the expression returns TRUE if one or more rows exist
and FALSE if the result set is empty.
If no terms in the SELECT expression refer to value in the containing
query, then the expression is evaluated once prior to any other
processing and the result is reused as necessary.  If the SELECT expression
does contain variables from the outer query, then the SELECT is reevaluated
every time it is needed.</p>

<p>When a SELECT is the right operand of the IN operator, the IN
operator returns TRUE if the result of the left operand is any of
the values generated by the select.  The IN operator may be preceded
by the NOT keyword to invert the sense of the test.</p>

<p>When a SELECT appears within an expression but is not the right
operand of an IN operator, then the first row of the result of the
SELECT becomes the value used in the expression.  If the SELECT yields
more than one result row, all rows after the first are ignored.  If
the SELECT yields no rows, then the value of the SELECT is NULL.</p>

<p>Both simple and aggregate functions are supported.  A simple
function can be used in any expression.  Simple functions return
a result immediately based on their inputs.  Aggregate functions
may only be used in a SELECT statement.  Aggregate functions compute
their result across all rows of the result set.</p>

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

<table border=0 cellpadding=10>
<tr>
<td valign="top" align="right" width=120>abs(<i>X</i>)</td>
<td valign="top">Return the absolute value of argument <i>X</i>.</td>
</tr>

<tr>
<td valign="top" align="right">coalesce(<i>X</i>,<i>Y</i>,...)</td>