Cql – cassandra query language

Editor's Notes

• #6: http://wiki.apache.org/cassandra/API#StructuresWritesLevelBehaviorANYEnsure that the write has been written to at least 1 node, including HintedHandoff recipients.ONEEnsure that the write has been written to at least 1 replica's commit log and memory table before responding to the client.QUORUMEnsure that the write has been written to N / 2 + 1 replicas before responding to the client.LOCAL_QUORUMEnsure that the write has been written to <ReplicationFactor> / 2 + 1 nodes, within the local datacenter (requires NetworkTopologyStrategy)EACH_QUORUMEnsure that the write has been written to <ReplicationFactor> / 2 + 1 nodes in each datacenter (requires NetworkTopologyStrategy)ALLEnsure that the write is written to all N replicas before responding to the client. Any unresponsive replicas will fail the operation.ReadsLevelBehaviorANYNot supported. You probably want ONE instead.ONEWill return the record returned by the first replica to respond. A consistency check is always done in a background thread to fix any consistency issues whenConsistencyLevel.ONE is used. This means subsequent calls will have correct data even if the initial read gets an older value. (This is called ReadRepair)QUORUMWill query all replicas and return the record with the most recent timestamp once it has at least a majority of replicas (N / 2 + 1) reported. Again, the remaining replicas will be checked in the background.LOCAL_QUORUMReturns the record with the most recent timestamp once a majority of replicas within the local datacenter have replied.EACH_QUORUMReturns the record with the most recent timestamp once a majority of replicas within each datacenter have replied.ALLWill query all replicas and return the record with the most recent timestamp once all replicas have replied. Any unresponsive replicas will fail the operation.
• #7: The CREATE KEYSPACE statement creates a new top-level namespace (aka “keyspace”). Valid names are any string constructed of alphanumeric characters and underscores, but must begin with a letter. Properties such as replication strategy and count are specified during creation using the following accepted keyword arguments:Keywordrequireddescriptionreplication_factor yes Numeric argument that specifies the number of replicas for this keyspace.strategy_class yes Class name to use for managing replica placement. Any of the shipped strategies can be used by specifying the class name relative to org.apache.cassandra.locator, others will need to be fully-qualified and located on the classpath.strategy_options no Some strategies require additional arguments which can be supplied by appending the option name to the strategy_options keyword, separated by a colon (:). For example, a strategy option of “DC1″ with a value of “1″ would be specified as strategy_options:DC1 = 1.Synopsis:CREATE COLUMNFAMILY [(name1 type, name2 type, ...)] [WITH keyword1 = arg1 [AND keyword2 = arg2 [AND ...]]]; CREATE COLUMNFAMILY statements create new column family namespaces under the current keyspace. Valid column family names are strings of alphanumeric characters and underscores, which begin with a letter.Specifying Column Type (optional)CREATE COLUMNFAMILY (name1 type, name2 type) ...; It is possible to assign columns a type during column family creation. Columns configured with a type are validated accordingly when a write occurs. Column types are specified as a parenthesized, comma-separated list of column term and type pairs. The list of recognized types are:Type descriptionBytes Arbitrary bytes (no validation)AsciiASCII character stringUtf8 UTF8 encoded stringTimeuuid Type 1 UUIDUuid Type 4 UUIDInt 4-byte integerLong 8-byte longNote: In addition to the recognized types listed above, it is also possible to supply a string containing the name of a class (a sub-class of AbstractType), either fully qualified, or relative to theorg.apache.cassandra.db.marshalpackage.Column Family Options (optional)CREATE COLUMNFAMILY ... WITH keyword1 = arg1 AND keyword2 = arg2; A number of optional keyword arguments can be supplied to control the configuration of a new column family.Keyword default descriptionComparator utf8 Determines sorting and validation of column names. Valid values are identical to the types listed in Specifying Column Type above.Comment none A free-form, human-readable comment.row_cache_size 0 Number of rows whose entire contents to cache in memory.key_cache_size 200000 Number of keys per SSTable whose locations are kept in memory in “mostly LRU” order.read_repair_chance 1.0 The probability with which read repairs should be invoked on non-quorum reads.gc_grace_seconds 864000 Time to wait before garbage collecting tombstones (deletion markers).default_validation utf8 Determines validation of column values. Valid values are identical to the types listed in Specifying Column Type above.min_compaction_threshold 4 Minimum number of SSTables needed to start a minor compaction.max_compaction_threshold 32 Maximum number of SSTables allowed before a minor compaction is forced.row_cache_save_period_in_seconds 0 Number of seconds between saving row caches.key_cache_save_period_in_seconds 14400 Number of seconds between saving key caches.memtable_flush_after_mins 60 Maximum time to leave a dirty table unflushed.memtable_throughput_in_mb dynamic Maximum size of the memtable before it is flushed.memtable_operations_in_millions dynamic Number of operations in millions before the memtable is flushed.replicate_on_write false
• #8: Synopsis:USE <KEYSPACE>; A USE statement consists of the USE keyword, followed by a valid keyspace name. Its purpose is to assign the per-connection, current working keyspace. All subsequent keyspace-specific actions will be performed in the context of the supplied value.Synopsis:DROP <KEYSPACE|COLUMNFAMILY> namespace; DROP statements result in the immediate, irreversible removal of keyspace and column family namespaces.
• #9: Synopsis:UPDATE [USING CONSISTENCY ] SET name1 = value1, name2 = value2 WHERE KEY = keyname; An UPDATE is used to write one or more columns to a record in a Cassandra column family. No results are returned.Column FamilyUPDATE <COLUMN FAMILY> ... Statements begin with the UPDATE keyword followed by a Cassandra column family name.Consistency LevelUPDATE ... [USING <CONSISTENCY>] ... Following the column family identifier is an optional consistency level specification.Specifying Columns and RowUPDATE ... SET name1 = value1, name2 = value2 WHERE KEY = keyname; Rows are created or updated by supplying column names and values in term assignment format. Multiple columns can be set by separating the name/value pairs using commas. Each update statement requires exactly one key to be specified using a WHERE clause and the KEY keyword.Additionally, it is also possible to send multiple UPDATES to a node at once using a batch syntax:BEGIN BATCH [USING ] UPDATE CF1 SET name1 = value1, name2 = value2 WHERE KEY = keyname1; UPDATE CF1 SET name3 = value3 WHERE KEY = keyname2; UPDATE CF2 SET name4 = value4, name5 = value5 WHERE KEY = keyname3; APPLY BATCH When batching UPDATEs, a single consistency level is used for the entire batch, it appears after the BEGIN BATCHstatement, and uses the standard consistency level specification. Batch UPDATEs default toCONSISTENCY.ONEwhen left unspecified.NOTE: While there are no isolation guarantees, UPDATE queries are atomic within a give record.
• #11: Synopsis:DELETE [COLUMNS] FROM [USING ] WHERE KEY = keyname1 DELETE [COLUMNS] FROM [USING ] WHERE KEY IN (keyname1, keyname2); A DELETE is used to perform the removal of one or more columns from one or more rows.Specifying ColumnsDELETE [COLUMNS] ... Following the DELETE keyword is an optional comma-delimited list of column name terms. When no column names are specified, the remove applies to the entire row(s) matched by the WHERE clauseColumn FamilyDELETE ... FROM <COLUMN FAMILY> ... The column family name follows the list of column names.Consistency LevelUPDATE ... [USING <CONSISTENCY>] ... Following the column family identifier is an optional consistency level specification.Specifying RowsUPDATE ... WHERE KEY = keyname1 UPDATE ... WHERE KEY IN (keyname1, keyname2) The WHERE clause is used to determine which row(s) a DELETE applies to. The first form allows the specification of a single keyname using the KEY keyword and the = operator. The second form allows a list of keyname terms to be specified using the IN notation and a parenthesized list of comma-delimited keyname terms.
• #12: Synopsis:SELECT [FIRST N] [REVERSED] <SELECT EXPR> FROM <COLUMN FAMILY> [USING <CONSISTENCY>] [WHERE <CLAUSE>] [LIMIT N]; A SELECT is used to read one or more records from a Cassandra column family. It returns a result-set of rows, where each row consists of a key and a collection of columns corresponding to the query.Specifying ColumnsSELECT [FIRST N] [REVERSED] name1, name2, name3 FROM ... SELECT [FIRST N] [REVERSED] name1..nameN FROM ... The SELECT expression determines which columns will appear in the results and takes the form of either a comma separated list of names, or a range. The range notation consists of a start and end column name separated by two periods (..). The set of columns returned for a range is start and end inclusive.The FIRST option accepts an integer argument and can be used to apply a limit to the number of columns returned per row. When this limit is left unset it defaults to 10,000 columns.The REVERSED option causes the sort order of the results to be reversed.It is worth noting that unlike the projection in a SQL SELECT, there is no guarantee that the results will contain all of the columns specified. This is because Cassandra is schema-less and there are no guarantees that a given column exists.Column FamilySELECT ... FROM <COLUMN FAMILY> ... The FROM clause is used to specify the Cassandra column family applicable to a SELECT query.Consistency LevelSELECT ... [USING <CONSISTENCY>] ... Following the column family clause is an optional consistency level specification.Filtering rowsSELECT ... WHERE KEY = keyname AND name1 = value1 SELECT ... WHERE KEY >= startkey and KEY =< endkey AND name1 = value1 The WHERE clause provides for filtering the rows that appear in results. The clause can filter on a key name, or range of keys, and in the case of indexed columns, on column values. Key filters are specified using the KEYkeyword, a relational operator, (one of =, >, >=, <, and <=), and a term value. When terms appear on both sides of a relational operator it is assumed the filter applies to an indexed column. With column index filters, the term on the left of the operator is the name, the term on the right is the value to filter on.Note: The greater-than and less-than operators (> and <) result in key ranges that are inclusive of the terms. There is no supported notion of “strictly” greater-than or less-than; these operators are merely supported as aliases to >=and <=.LimitsSELECT ... WHERE <CLAUSE> [LIMIT N] ... Limiting the number of rows returned can be achieved by adding the LIMIT option to a SELECT expression. LIMITdefaults to 10,000 when left unset.