Author: tylerhobbs
Date: Tue Mar 3 20:05:46 2015
New Revision: 1663774
URL: http://svn.apache.org/r1663774
Log:
Update CQL3 docs for CASSANDRA-8889
Modified:
cassandra/site/publish/doc/cql3/CQL-2.0.html
cassandra/site/publish/doc/cql3/CQL-2.1.html
Modified: cassandra/site/publish/doc/cql3/CQL-2.0.html
URL:
http://svn.apache.org/viewvc/cassandra/site/publish/doc/cql3/CQL-2.0.html?rev=1663774&r1=1663773&r2=1663774&view=diff
==============================================================================
--- cassandra/site/publish/doc/cql3/CQL-2.0.html (original)
+++ cassandra/site/publish/doc/cql3/CQL-2.0.html Tue Mar 3 20:05:46 2015
@@ -38,7 +38,7 @@
<properties> ::= <property> (AND <property>)*
<property> ::= <identifier> '=' ( <identifier> | <constant> |
<map-literal> )
-</pre></pre><p><br/>Please note that not every possible productions of the
grammar above will be valid in practice. Most notably,
<code><variable></code> and nested <code><collection-literal></code> are
currently not allowed inside <code><collection-literal></code>.</p><p>A
<code><variable></code> can be either anonymous (a question mark
(<code>?</code>)) or named (an identifier preceded by <code>:</code>). Both
declare a bind variables for <a href="#preparedStatement">prepared
statements</a>. The only difference between an anymous and a named variable is
that a named one will be easier to refer to (how exactly depends on the client
driver used).</p><p>The <code><properties></code> production is use by
statement that create and alter keyspaces and tables. Each
<code><property></code> is either a <em>simple</em> one, in which case it
just has a value, or a <em>map</em> one, in which case it’s value is a
map grouping sub-options. The following will refer to one
or the other as the <em>kind</em> (<em>simple</em> or <em>map</em>) of the
property.</p><p>A <code><tablename></code> will be used to identify a table.
This is an identifier representing the table name that can be preceded by a
keyspace name. The keyspace name, if provided, allow to identify a table in
another keyspace than the currently active one (the currently active keyspace
is set through the <a href="#useStmt"><tt>USE</tt></a> statement).</p><p>For
supported <code><function></code>, see the section on <a
href="#functions">functions</a>.</p><h3 id="preparedStatement">Prepared
Statement</h3><p>CQL supports <em>prepared statements</em>. Prepared statement
is an optimization that allows to parse a query only once but execute it
multiple times with different concrete values.</p><p>In a statement, each time
a column value is expected (in the data manipulation and query statements), a
<code><variable></code> (see above) can be used instead. A statement with
bind variables m
ust then be <em>prepared</em>. Once it has been prepared, it can executed by
providing concrete values for the bind variables. The exact procedure to
prepare a statement and execute a prepared statement depends on the CQL driver
used and is beyond the scope of this document.</p><h2 id="dataDefinition">Data
Definition</h2><h3 id="createKeyspaceStmt">CREATE
KEYSPACE</h3><p><i>Syntax:</i></p><pre
class="syntax"><pre><create-keyspace-stmt> ::= CREATE KEYSPACE (IF NOT
EXISTS)? <identifier> WITH <properties>
+</pre></pre><p><br/>Please note that not every possible productions of the
grammar above will be valid in practice. Most notably,
<code><variable></code> and nested <code><collection-literal></code> are
currently not allowed inside <code><collection-literal></code>.</p><p>A
<code><variable></code> can be either anonymous (a question mark
(<code>?</code>)) or named (an identifier preceded by <code>:</code>). Both
declare a bind variables for <a href="#preparedStatement">prepared
statements</a>. The only difference between an anymous and a named variable is
that a named one will be easier to refer to (how exactly depends on the client
driver used).</p><p>The <code><properties></code> production is use by
statement that create and alter keyspaces and tables. Each
<code><property></code> is either a <em>simple</em> one, in which case it
just has a value, or a <em>map</em> one, in which case it’s value is a
map grouping sub-options. The following will refer to one
or the other as the <em>kind</em> (<em>simple</em> or <em>map</em>) of the
property.</p><p>A <code><tablename></code> will be used to identify a table.
This is an identifier representing the table name that can be preceded by a
keyspace name. The keyspace name, if provided, allow to identify a table in
another keyspace than the currently active one (the currently active keyspace
is set through the <a href="#useStmt"><tt>USE</tt></a> statement).</p><p>For
supported <code><function></code>, see the section on <a
href="#functions">functions</a>.</p><h3 id="preparedStatement">Prepared
Statement</h3><p>CQL supports <em>prepared statements</em>. Prepared statement
is an optimization that allows to parse a query only once but execute it
multiple times with different concrete values.</p><p>In a statement, each time
a column value is expected (in the data manipulation and query statements), a
<code><variable></code> (see above) can be used instead. A statement with
bind variables m
ust then be <em>prepared</em>. Once it has been prepared, it can executed by
providing concrete values for the bind variables. The exact procedure to
prepare a statement and execute a prepared statement depends on the CQL driver
used and is beyond the scope of this document.</p><p>In addition to providing
column values, bind markers may be used to provide values for
<code>LIMIT</code>, <code>TIMESTAMP</code>, and <code>TTL</code> clauses. If
anonymous bind markers are used, the names for the query parameters will be
<code>[limit]</code>, <code>[timestamp]</code>, and <code>[ttl]</code>,
respectively.</p><h2 id="dataDefinition">Data Definition</h2><h3
id="createKeyspaceStmt">CREATE KEYSPACE</h3><p><i>Syntax:</i></p><pre
class="syntax"><pre><create-keyspace-stmt> ::= CREATE KEYSPACE (IF NOT
EXISTS)? <identifier> WITH <properties>
</pre></pre><p><br/><i>Sample:</i></p><pre class="sample"><pre>CREATE KEYSPACE
Excelsior
WITH replication = {'class': 'SimpleStrategy', 'replication_factor'
: 3};
@@ -101,7 +101,7 @@ CREATE TABLE timeline (
INSERT INTO test(pk, t, v, s) VALUES (0, 0, 'val0', 'static0');
INSERT INTO test(pk, t, v, s) VALUES (0, 1, 'val1', 'static1');
SELECT * FROM test WHERE pk=0 AND t=0;
-</pre></pre><p>the last query will return <code>'static1'</code> as value for
<code>s</code>, since <code>s</code> is static and thus the 2nd insertion
modified this “shared” value. Note however that static columns are
only static within a given partition, and if in the example above both rows
where from different partitions (i.e. if they had different value for
<code>pk</code>), then the 2nd insertion would not have modified the value of
<code>s</code> for the first row.</p><p>A few restrictions applies to when
static columns are allowed:</p><ul><li>tables with the <code>COMPACT
STORAGE</code> option (see below) cannot have them</li><li>a table without
clustering columns cannot have static columns (in a table without clustering
columns, every partition has only one row, and so every column is inherently
static).</li><li>only non <code>PRIMARY KEY</code> columns can be
static</li></ul><h4 id="createTableOptions"><code><option></code></h4><p>The
<code>CREATE TABLE</cod
e> statement supports a number of options that controls the configuration of a
new table. These options can be specified after the <code>WITH</code>
keyword.</p><p>The first of these option is <code>COMPACT STORAGE</code>. This
option is mainly targeted towards backward compatibility for definitions
created before CQL3 (see <a
href="http://www.datastax.com/dev/blog/thrift-to-cql3";>www.datastax.com/dev/blog/thrift-to-cql3</a>
for more details). The option also provides a slightly more compact layout of
data on disk but at the price of diminished flexibility and extensibility for
the table. Most notably, <code>COMPACT STORAGE</code> tables cannot have
collections nor static columns and a <code>COMPACT STORAGE</code> table with at
least one clustering column supports exactly one (as in not 0 nor more than 1)
column not part of the <code>PRIMARY KEY</code> definition (which imply in
particular that you cannot add nor remove columns after creation). For those
reasons, <code>COMPACT STO
RAGE</code> is not recommended outside of the backward compatibility reason
evoked above.</p><p>Another option is <code>CLUSTERING ORDER</code>. It allows
to define the ordering of rows on disk. It takes the list of the clustering
column names with, for each of them, the on-disk order (Ascending or
descending). Note that this option affects <a href="#selectOrderBy">what
<code>ORDER BY</code> are allowed during <code>SELECT</code></a>.</p><p>Table
creation supports the following other
<code><property></code>:</p><table><tr><th>option
</th><th>kind </th><th>default
</th><th>description</th></tr><tr><td><code>comment</code>
</td><td><em>simple</em> </td><td>none </td><td>A free-form,
human-readable comment.</td></tr><tr><td><code>read_repair_chance</code>
</td><td><em>simple</em> </td><td>0.1 </td><td>The probability with
which to query extra nodes (e.g. more nodes than required by the consistency
level) for the purpos
e of read repairs.</td></tr><tr><td><code>dclocal_read_repair_chance</code>
</td><td><em>simple</em> </td><td>0 </td><td>The probability with
which to query extra nodes (e.g. more nodes than required by the consistency
level) belonging to the same data center than the read coordinator for the
purpose of read repairs.</td></tr><tr><td><code>gc_grace_seconds</code>
</td><td><em>simple</em> </td><td>864000 </td><td>Time to wait before
garbage collecting tombstones (deletion
markers).</td></tr><tr><td><code>bloom_filter_fp_chance</code>
</td><td><em>simple</em> </td><td>0.00075 </td><td>The target probability
of false positive of the sstable bloom filters. Said bloom filters will be
sized to provide the provided probability (thus lowering this value impact the
size of bloom filters in-memory and
on-disk)</td></tr><tr><td><code>compaction</code>
</td><td><em>map</em> </td><td><em>see below</em> </td><td>The compaction
options to use, se
e below.</td></tr><tr><td><code>compression</code>
</td><td><em>map</em> </td><td><em>see below</em> </td><td>Compression
options, see below. </td></tr><tr><td><code>replicate_on_write</code>
</td><td><em>simple</em> </td><td>true </td><td>Whether to replicate
data on write. This can only be set to false for tables with counters values.
Disabling this is dangerous and can result in random lose of counters,
don’t disable unless you are sure to know what you are
doing</td></tr><tr><td><code>caching</code>
</td><td><em>simple</em> </td><td>keys_only </td><td>Whether to cache keys
(“key cache”) and/or rows (“row cache”) for this table.
Valid values are: <code>all</code>, <code>keys_only</code>,
<code>rows_only</code> and <code>none</code>. </td></tr></table><h4
id="compactionOptions"><code>compaction</code> options</h4><p>The
<code>compaction</code> property must at least define the <code>'class'</code>
sub-option, that defines the compaction strategy class to use. The default
supported class are <code>'SizeTieredCompactionStrategy'</code> and
<code>'LeveledCompactionStrategy'</code>. Custom strategy can be provided by
specifying the full class name as a <a href="#constants">string constant</a>.
The rest of the sub-options depends on the chosen class. The sub-options
supported by the default classes are:</p><table><tr><th>option
</th><th>supported compaction strategy </th><th>default
</th><th>description </th></tr><tr><td><code>enabled</code>
</td><td><em>all</em> </td><td>true
</td><td>A boolean denoting whether compaction should be enabled or
not.</td></tr><tr><td><code>tombstone_threshold</code>
</td><td><em>all</em> </td><td>0.2 </td><td>A
ratio such that if a sstable has more than this ratio of gcable tombstones over
all contained columns, the sstable will b
e compacted (with no other sstables) for the purpose of purging those
tombstones. </td></tr><tr><td><code>tombstone_compaction_interval</code>
</td><td><em>all</em> </td><td>1 day </td><td>The
minimum time to wait after an sstable creation time before considering it for
“tombstone compaction”, where “tombstone compaction” is
the compaction triggered if the sstable has more gcable tombstones than
<code>tombstone_threshold</code>.
</td></tr><tr><td><code>unchecked_tombstone_compaction</code>
</td><td><em>all</em> </td><td>false
</td><td>Setting this to true enables more aggressive tombstone compactions
– single sstable tombstone compactions will run without checking how
likely it is that they will be successful.
</td></tr><tr><td><code>min_sstable_size</code>
</td><td>SizeTieredCompactionStrategy </td><td>50MB </td><td>The size
tiered strategy groups SSTables to compact in b
uckets. A bucket groups SSTables that differs from less than 50% in size.
However, for small sizes, this would result in a bucketing that is too fine
grained. <code>min_sstable_size</code> defines a size threshold (in bytes)
below which all SSTables belong to one unique
bucket</td></tr><tr><td><code>min_threshold</code>
</td><td>SizeTieredCompactionStrategy </td><td>4 </td><td>Minimum
number of SSTables needed to start a minor
compaction.</td></tr><tr><td><code>max_threshold</code>
</td><td>SizeTieredCompactionStrategy </td><td>32 </td><td>Maximum
number of SSTables processed by one minor
compaction.</td></tr><tr><td><code>bucket_low</code>
</td><td>SizeTieredCompactionStrategy </td><td>0.5 </td><td>Size
tiered consider sstables to be within the same bucket if their size is within
[average_size * <code>bucket_low</code>, average_size *
<code>bucket_high</code> ] (i.e the default groups sstable whose
sizes diverges by at most 50%)</td></tr><tr><td><code>bucket_high</code>
</td><td>SizeTieredCompactionStrategy </td><td>1.5
</td><td>Size tiered consider sstables to be within the same bucket if their
size is within [average_size * <code>bucket_low</code>, average_size *
<code>bucket_high</code> ] (i.e the default groups sstable whose sizes diverges
by at most 50%).</td></tr><tr><td><code>sstable_size_in_mb</code>
</td><td>LeveledCompactionStrategy </td><td>5MB </td><td>The target
size (in MB) for sstables in the leveled strategy. Note that while sstable
sizes should stay less or equal to <code>sstable_size_in_mb</code>, it is
possible to exceptionally have a larger sstable as during compaction, data for
a given partition key are never split into 2 sstables</td></tr></table><p>For
the <code>compression</code> property, the following default sub-options are
available:</p><table><tr><th>option </th><th>default </
th><th>description </th></tr><tr><td><code>sstable_compression</code>
</td><td>LZ4Compressor </td><td>The compression algorithm to use. Default
compressor are: LZ4Compressor, SnappyCompressor and DeflateCompressor. Use an
empty string (<code>''</code>) to disable compression. Custom compressor can be
provided by specifying the full class name as a <a href="#constants">string
constant</a>.</td></tr><tr><td><code>chunk_length_kb</code> </td><td>64KB
</td><td>On disk SSTables are compressed by block (to allow random
reads). This defines the size (in KB) of said block. Bigger values may improve
the compression rate, but increases the minimum size of data to be read from
disk for a read </td></tr><tr><td><code>crc_check_chance</code> </td><td>1.0
</td><td>When compression is enabled, each compressed block
includes a checksum of that block for the purpose of detecting disk bitrot and
avoiding the propagation of corruption to other replica. This option de
fines the probability with which those checksums are checked during read. By
default they are always checked. Set to 0 to disable checksum checking and to
0.5 for instance to check them every other read</td></tr></table><h4
id="Otherconsiderations">Other considerations:</h4><ul><li>When <a
href="#insertStmt/"updating":#updateStmt">inserting</a> a given row,
not all columns needs to be defined (except for those part of the key), and
missing columns occupy no space on disk. Furthermore, adding new columns (see
<a href=#alterStmt><tt>ALTER TABLE</tt></a>) is a constant time operation.
There is thus no need to try to anticipate future usage (or to cry when you
haven’t) when creating a table.</li></ul><h3 id="alterTableStmt">ALTER
TABLE</h3><p><i>Syntax:</i></p><pre class="syntax"><pre><alter-table-stmt>
::= ALTER (TABLE | COLUMNFAMILY) <tablename> <instruction>
+</pre></pre><p>the last query will return <code>'static1'</code> as value for
<code>s</code>, since <code>s</code> is static and thus the 2nd insertion
modified this “shared” value. Note however that static columns are
only static within a given partition, and if in the example above both rows
where from different partitions (i.e. if they had different value for
<code>pk</code>), then the 2nd insertion would not have modified the value of
<code>s</code> for the first row.</p><p>A few restrictions applies to when
static columns are allowed:</p><ul><li>tables with the <code>COMPACT
STORAGE</code> option (see below) cannot have them</li><li>a table without
clustering columns cannot have static columns (in a table without clustering
columns, every partition has only one row, and so every column is inherently
static).</li><li>only non <code>PRIMARY KEY</code> columns can be
static</li></ul><h4 id="createTableOptions"><code><option></code></h4><p>The
<code>CREATE TABLE</cod
e> statement supports a number of options that controls the configuration of a
new table. These options can be specified after the <code>WITH</code>
keyword.</p><p>The first of these option is <code>COMPACT STORAGE</code>. This
option is mainly targeted towards backward compatibility for definitions
created before CQL3 (see <a
href="http://www.datastax.com/dev/blog/thrift-to-cql3";>www.datastax.com/dev/blog/thrift-to-cql3</a>
for more details). The option also provides a slightly more compact layout of
data on disk but at the price of diminished flexibility and extensibility for
the table. Most notably, <code>COMPACT STORAGE</code> tables cannot have
collections nor static columns and a <code>COMPACT STORAGE</code> table with at
least one clustering column supports exactly one (as in not 0 nor more than 1)
column not part of the <code>PRIMARY KEY</code> definition (which imply in
particular that you cannot add nor remove columns after creation). For those
reasons, <code>COMPACT STO
RAGE</code> is not recommended outside of the backward compatibility reason
evoked above.</p><p>Another option is <code>CLUSTERING ORDER</code>. It allows
to define the ordering of rows on disk. It takes the list of the clustering
column names with, for each of them, the on-disk order (Ascending or
descending). Note that this option affects <a href="#selectOrderBy">what
<code>ORDER BY</code> are allowed during <code>SELECT</code></a>.</p><p>Table
creation supports the following other
<code><property></code>:</p><table><tr><th>option
</th><th>kind </th><th>default
</th><th>description</th></tr><tr><td><code>comment</code>
</td><td><em>simple</em> </td><td>none </td><td>A free-form,
human-readable comment.</td></tr><tr><td><code>read_repair_chance</code>
</td><td><em>simple</em> </td><td>0.1 </td><td>The probability with
which to query extra nodes (e.g. more nodes than required by the consistency
level) for the purpos
e of read repairs.</td></tr><tr><td><code>dclocal_read_repair_chance</code>
</td><td><em>simple</em> </td><td>0 </td><td>The probability with
which to query extra nodes (e.g. more nodes than required by the consistency
level) belonging to the same data center than the read coordinator for the
purpose of read repairs.</td></tr><tr><td><code>gc_grace_seconds</code>
</td><td><em>simple</em> </td><td>864000 </td><td>Time to wait before
garbage collecting tombstones (deletion
markers).</td></tr><tr><td><code>bloom_filter_fp_chance</code>
</td><td><em>simple</em> </td><td>0.00075 </td><td>The target probability
of false positive of the sstable bloom filters. Said bloom filters will be
sized to provide the provided probability (thus lowering this value impact the
size of bloom filters in-memory and
on-disk)</td></tr><tr><td><code>compaction</code>
</td><td><em>map</em> </td><td><em>see below</em> </td><td>The compaction
options to use, se
e below.</td></tr><tr><td><code>compression</code>
</td><td><em>map</em> </td><td><em>see below</em> </td><td>Compression
options, see below. </td></tr><tr><td><code>replicate_on_write</code>
</td><td><em>simple</em> </td><td>true </td><td>Whether to replicate
data on write. This can only be set to false for tables with counters values.
Disabling this is dangerous and can result in random lose of counters,
don’t disable unless you are sure to know what you are
doing</td></tr><tr><td><code>caching</code>
</td><td><em>simple</em> </td><td>keys_only </td><td>Whether to cache keys
(“key cache”) and/or rows (“row cache”) for this table.
Valid values are: <code>all</code>, <code>keys_only</code>,
<code>rows_only</code> and <code>none</code>.
</td></tr><tr><td><code>default_time_to_live</code>
</td><td><em>simple</em> </td><td>0 </td><td>The default expiration
time (“TTL”) in sec
onds for a table.</td></tr></table><h4
id="compactionOptions"><code>compaction</code> options</h4><p>The
<code>compaction</code> property must at least define the <code>'class'</code>
sub-option, that defines the compaction strategy class to use. The default
supported class are <code>'SizeTieredCompactionStrategy'</code> and
<code>'LeveledCompactionStrategy'</code>. Custom strategy can be provided by
specifying the full class name as a <a href="#constants">string constant</a>.
The rest of the sub-options depends on the chosen class. The sub-options
supported by the default classes are:</p><table><tr><th>option
</th><th>supported compaction strategy </th><th>default
</th><th>description </th></tr><tr><td><code>enabled</code>
</td><td><em>all</em> </td><td>true
</td><td>A boolean denoting whether compaction should be enabled or
not.</td></tr><tr><td><code>tombstone_threshold</code>
</td><td><em>al
l</em> </td><td>0.2 </td><td>A ratio such that
if a sstable has more than this ratio of gcable tombstones over all contained
columns, the sstable will be compacted (with no other sstables) for the purpose
of purging those tombstones.
</td></tr><tr><td><code>tombstone_compaction_interval</code>
</td><td><em>all</em> </td><td>1 day </td><td>The
minimum time to wait after an sstable creation time before considering it for
“tombstone compaction”, where “tombstone compaction” is
the compaction triggered if the sstable has more gcable tombstones than
<code>tombstone_threshold</code>.
</td></tr><tr><td><code>unchecked_tombstone_compaction</code>
</td><td><em>all</em> </td><td>false
</td><td>Setting this to true enables more aggressive tombstone compactions
– single sstable tombstone compactions will run without checking how
likely it is that they will be successful. </t
d></tr><tr><td><code>min_sstable_size</code>
</td><td>SizeTieredCompactionStrategy </td><td>50MB </td><td>The size
tiered strategy groups SSTables to compact in buckets. A bucket groups SSTables
that differs from less than 50% in size. However, for small sizes, this would
result in a bucketing that is too fine grained. <code>min_sstable_size</code>
defines a size threshold (in bytes) below which all SSTables belong to one
unique bucket</td></tr><tr><td><code>min_threshold</code>
</td><td>SizeTieredCompactionStrategy </td><td>4 </td><td>Minimum
number of SSTables needed to start a minor
compaction.</td></tr><tr><td><code>max_threshold</code>
</td><td>SizeTieredCompactionStrategy </td><td>32 </td><td>Maximum
number of SSTables processed by one minor
compaction.</td></tr><tr><td><code>bucket_low</code>
</td><td>SizeTieredCompactionStrategy </td><td>0.5 </td><td>Size
tiered conside
r sstables to be within the same bucket if their size is within [average_size
* <code>bucket_low</code>, average_size * <code>bucket_high</code> ] (i.e the
default groups sstable whose sizes diverges by at most
50%)</td></tr><tr><td><code>bucket_high</code>
</td><td>SizeTieredCompactionStrategy </td><td>1.5 </td><td>Size
tiered consider sstables to be within the same bucket if their size is within
[average_size * <code>bucket_low</code>, average_size *
<code>bucket_high</code> ] (i.e the default groups sstable whose sizes diverges
by at most 50%).</td></tr><tr><td><code>sstable_size_in_mb</code>
</td><td>LeveledCompactionStrategy </td><td>5MB </td><td>The target
size (in MB) for sstables in the leveled strategy. Note that while sstable
sizes should stay less or equal to <code>sstable_size_in_mb</code>, it is
possible to exceptionally have a larger sstable as during compaction, data for
a given partition key are never split into 2 s
stables</td></tr></table><p>For the <code>compression</code> property, the
following default sub-options are available:</p><table><tr><th>option
</th><th>default </th><th>description
</th></tr><tr><td><code>sstable_compression</code> </td><td>LZ4Compressor
</td><td>The compression algorithm to use. Default compressor are:
LZ4Compressor, SnappyCompressor and DeflateCompressor. Use an empty string
(<code>''</code>) to disable compression. Custom compressor can be provided by
specifying the full class name as a <a href="#constants">string
constant</a>.</td></tr><tr><td><code>chunk_length_kb</code> </td><td>64KB
</td><td>On disk SSTables are compressed by block (to allow random
reads). This defines the size (in KB) of said block. Bigger values may improve
the compression rate, but increases the minimum size of data to be read from
disk for a read </td></tr><tr><td><code>crc_check_chance</code> </td><td>1.0
</td><td>When compression
is enabled, each compressed block includes a checksum of that block for the
purpose of detecting disk bitrot and avoiding the propagation of corruption to
other replica. This option defines the probability with which those checksums
are checked during read. By default they are always checked. Set to 0 to
disable checksum checking and to 0.5 for instance to check them every other
read</td></tr></table><h4 id="Otherconsiderations">Other
considerations:</h4><ul><li>When <a
href="#insertStmt/"updating":#updateStmt">inserting</a> a given row,
not all columns needs to be defined (except for those part of the key), and
missing columns occupy no space on disk. Furthermore, adding new columns (see
<a href=#alterStmt><tt>ALTER TABLE</tt></a>) is a constant time operation.
There is thus no need to try to anticipate future usage (or to cry when you
haven’t) when creating a table.</li></ul><h3 id="alterTableStmt">ALTER
TABLE</h3><p><i>Syntax:</i></p><pre class="syntax"><pre>&l
t;alter-table-stmt> ::= ALTER (TABLE | COLUMNFAMILY) <tablename>
<instruction>
<instruction> ::= ALTER <identifier> TYPE <type>
| ADD <identifier> <type>
@@ -171,7 +171,7 @@ SET director = 'Joss Whedon',
WHERE movie = 'Serenity';
UPDATE UserActions SET total = total + 2 WHERE user =
B70DE1D0-9908-4AE3-BE34-5573E5B09F14 AND action = 'click';
-</pre></pre><p><br/>The <code>UPDATE</code> statement writes one or more
columns for a given row in a table. The <code><where-clause></code> is used
to select the row to update and must include all columns composing the
<code>PRIMARY KEY</code> (the <code>IN</code> relation is only supported for
the last column of the partition key). Other columns values are specified
through <code><assignment></code> after the <code>SET</code>
keyword.</p><p>Note that unlike in SQL, <code>UPDATE</code> does not check the
prior existence of the row by default: the row is created if none existed
before, and updated otherwise. Furthermore, there is no mean to know which of
creation or update happened.</p><p>It is however possible to use the conditions
on some columns through <code>IF</code>, in which case the row will not be
updated unless such condition are met. But please note that using
<code>IF</code> conditions will incur a non negligible performance cost
(internally, Paxos will be used) so
this should be used sparingly.</p><p>In an <code>UPDATE</code> statement, all
updates within the same partition key are applied atomically and in
isolation.</p><p>The <code>c = c + 3</code> form of
<code><assignment></code> is used to increment/decrement counters. The
identifier after the ‘=’ sign <strong>must</strong> be the same
than the one before the ‘=’ sign (Only increment/decrement is
supported on counters, not the assignment of a specific value).</p><p>The
<code>id = id + <collection-literal></code> and <code>id[value1] =
value2</code> forms of <code><assignment></code> are for collections. Please
refer to the <a href="#collections">relevant section</a> for more
details.</p><h4 id="updateOptions"><code><options></code></h4><p>The
<code>UPDATE</code> and <code>INSERT</code> statements allows to specify the
following options for the insertion:</p><ul><li><code>TIMESTAMP</code>: sets
the timestamp for the operation. If not specified, the cur
rent time of the insertion (in microseconds) is used. This is usually a
suitable default.</li><li><code>TTL</code>: allows to specify an optional Time
To Live (in seconds) for the inserted values. If set, the inserted values are
automatically removed from the database after the specified time. Note that the
TTL concerns the inserted values, not the column themselves. This means that
any subsequent update of the column will also reset the TTL (to whatever TTL is
specified in that update). By default, values never expire. A TTL of 0 or a
negative one is equivalent to no TTL.</li></ul><h3
id="deleteStmt">DELETE</h3><p><i>Syntax:</i></p><pre
class="syntax"><pre><delete-stmt> ::= DELETE ( <selection> ( ','
<selection> )* )?
+</pre></pre><p><br/>The <code>UPDATE</code> statement writes one or more
columns for a given row in a table. The <code><where-clause></code> is used
to select the row to update and must include all columns composing the
<code>PRIMARY KEY</code> (the <code>IN</code> relation is only supported for
the last column of the partition key). Other columns values are specified
through <code><assignment></code> after the <code>SET</code>
keyword.</p><p>Note that unlike in SQL, <code>UPDATE</code> does not check the
prior existence of the row by default: the row is created if none existed
before, and updated otherwise. Furthermore, there is no mean to know which of
creation or update happened.</p><p>It is however possible to use the conditions
on some columns through <code>IF</code>, in which case the row will not be
updated unless such condition are met. But please note that using
<code>IF</code> conditions will incur a non negligible performance cost
(internally, Paxos will be used) so
this should be used sparingly.</p><p>In an <code>UPDATE</code> statement, all
updates within the same partition key are applied atomically and in
isolation.</p><p>The <code>c = c + 3</code> form of
<code><assignment></code> is used to increment/decrement counters. The
identifier after the ‘=’ sign <strong>must</strong> be the same
than the one before the ‘=’ sign (Only increment/decrement is
supported on counters, not the assignment of a specific value).</p><p>The
<code>id = id + <collection-literal></code> and <code>id[value1] =
value2</code> forms of <code><assignment></code> are for collections. Please
refer to the <a href="#collections">relevant section</a> for more
details.</p><h4 id="updateOptions"><code><options></code></h4><p>The
<code>UPDATE</code> and <code>INSERT</code> statements allows to specify the
following options for the insertion:</p><ul><li><code>TIMESTAMP</code>: sets
the timestamp for the operation. If not specified, the coo
rdinator will use the current time (in microseconds) at the start of statement
execution as the timestamp. This is usually a suitable
default.</li><li><code>TTL</code>: allows to specify an optional Time To Live
(in seconds) for the inserted values. If set, the inserted values are
automatically removed from the database after the specified time. Note that the
TTL concerns the inserted values, not the column themselves. This means that
any subsequent update of the column will also reset the TTL (to whatever TTL is
specified in that update). By default, values never expire. A TTL of 0 or a
negative one is equivalent to no TTL.</li></ul><h3
id="deleteStmt">DELETE</h3><p><i>Syntax:</i></p><pre
class="syntax"><pre><delete-stmt> ::= DELETE ( <selection> ( ','
<selection> )* )?
FROM <tablename>
( USING TIMESTAMP <integer>)?
WHERE <where-clause>
Modified: cassandra/site/publish/doc/cql3/CQL-2.1.html
URL:
http://svn.apache.org/viewvc/cassandra/site/publish/doc/cql3/CQL-2.1.html?rev=1663774&r1=1663773&r2=1663774&view=diff
==============================================================================
--- cassandra/site/publish/doc/cql3/CQL-2.1.html (original)
+++ cassandra/site/publish/doc/cql3/CQL-2.1.html Tue Mar 3 20:05:46 2015
@@ -38,7 +38,7 @@
<properties> ::= <property> (AND <property>)*
<property> ::= <identifier> '=' ( <identifier> | <constant> |
<map-literal> )
-</pre></pre><p><br/>Please note that not every possible productions of the
grammar above will be valid in practice. Most notably,
<code><variable></code> and nested <code><collection-literal></code> are
currently not allowed inside <code><collection-literal></code>.</p><p>A
<code><variable></code> can be either anonymous (a question mark
(<code>?</code>)) or named (an identifier preceded by <code>:</code>). Both
declare a bind variables for <a href="#preparedStatement">prepared
statements</a>. The only difference between an anymous and a named variable is
that a named one will be easier to refer to (how exactly depends on the client
driver used).</p><p>The <code><properties></code> production is use by
statement that create and alter keyspaces and tables. Each
<code><property></code> is either a <em>simple</em> one, in which case it
just has a value, or a <em>map</em> one, in which case it’s value is a
map grouping sub-options. The following will refer to one
or the other as the <em>kind</em> (<em>simple</em> or <em>map</em>) of the
property.</p><p>A <code><tablename></code> will be used to identify a table.
This is an identifier representing the table name that can be preceded by a
keyspace name. The keyspace name, if provided, allow to identify a table in
another keyspace than the currently active one (the currently active keyspace
is set through the <a href="#useStmt"><tt>USE</tt></a> statement).</p><p>For
supported <code><function></code>, see the section on <a
href="#functions">functions</a>.</p><h3 id="preparedStatement">Prepared
Statement</h3><p>CQL supports <em>prepared statements</em>. Prepared statement
is an optimization that allows to parse a query only once but execute it
multiple times with different concrete values.</p><p>In a statement, each time
a column value is expected (in the data manipulation and query statements), a
<code><variable></code> (see above) can be used instead. A statement with
bind variables m
ust then be <em>prepared</em>. Once it has been prepared, it can executed by
providing concrete values for the bind variables. The exact procedure to
prepare a statement and execute a prepared statement depends on the CQL driver
used and is beyond the scope of this document.</p><h2 id="dataDefinition">Data
Definition</h2><h3 id="createKeyspaceStmt">CREATE
KEYSPACE</h3><p><i>Syntax:</i></p><pre
class="syntax"><pre><create-keyspace-stmt> ::= CREATE KEYSPACE (IF NOT
EXISTS)? <identifier> WITH <properties>
+</pre></pre><p><br/>Please note that not every possible productions of the
grammar above will be valid in practice. Most notably,
<code><variable></code> and nested <code><collection-literal></code> are
currently not allowed inside <code><collection-literal></code>.</p><p>A
<code><variable></code> can be either anonymous (a question mark
(<code>?</code>)) or named (an identifier preceded by <code>:</code>). Both
declare a bind variables for <a href="#preparedStatement">prepared
statements</a>. The only difference between an anymous and a named variable is
that a named one will be easier to refer to (how exactly depends on the client
driver used).</p><p>The <code><properties></code> production is use by
statement that create and alter keyspaces and tables. Each
<code><property></code> is either a <em>simple</em> one, in which case it
just has a value, or a <em>map</em> one, in which case it’s value is a
map grouping sub-options. The following will refer to one
or the other as the <em>kind</em> (<em>simple</em> or <em>map</em>) of the
property.</p><p>A <code><tablename></code> will be used to identify a table.
This is an identifier representing the table name that can be preceded by a
keyspace name. The keyspace name, if provided, allow to identify a table in
another keyspace than the currently active one (the currently active keyspace
is set through the <a href="#useStmt"><tt>USE</tt></a> statement).</p><p>For
supported <code><function></code>, see the section on <a
href="#functions">functions</a>.</p><h3 id="preparedStatement">Prepared
Statement</h3><p>CQL supports <em>prepared statements</em>. Prepared statement
is an optimization that allows to parse a query only once but execute it
multiple times with different concrete values.</p><p>In a statement, each time
a column value is expected (in the data manipulation and query statements), a
<code><variable></code> (see above) can be used instead. A statement with
bind variables m
ust then be <em>prepared</em>. Once it has been prepared, it can executed by
providing concrete values for the bind variables. The exact procedure to
prepare a statement and execute a prepared statement depends on the CQL driver
used and is beyond the scope of this document.</p><p>In addition to providing
column values, bind markers may be used to provide values for
<code>LIMIT</code>, <code>TIMESTAMP</code>, and <code>TTL</code> clauses. If
anonymous bind markers are used, the names for the query parameters will be
<code>[limit]</code>, <code>[timestamp]</code>, and <code>[ttl]</code>,
respectively.</p><h2 id="dataDefinition">Data Definition</h2><h3
id="createKeyspaceStmt">CREATE KEYSPACE</h3><p><i>Syntax:</i></p><pre
class="syntax"><pre><create-keyspace-stmt> ::= CREATE KEYSPACE (IF NOT
EXISTS)? <identifier> WITH <properties>
</pre></pre><p><br/><i>Sample:</i></p><pre class="sample"><pre>CREATE KEYSPACE
Excelsior
WITH replication = {'class': 'SimpleStrategy', 'replication_factor'
: 3};
