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https://issues.apache.org/jira/browse/TRAFODION-1419?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14642739#comment-14642739
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Qifan Chen commented on TRAFODION-1419:
---------------------------------------
May need to cover these statements as well.
1. CREATE TABLE LIKE: columns are grouped into families the same way as in the
SOURCE table
2. UPDATE STATS, like DMLs, do not need to reference column families.
3. ALTER TABLE: do we allow a column to move from one family to another?
4. KEY COLUMNS can not be split among different column families
On Syntax to specify a column family, I wonder if we can use hints to group a
group of columns for a single family without repeating the family name per
column, something like the following, where C1 and C2 are in family A and C3
and C4 in family B.
create table T (
<<+ family A >>
C1 INT,
C2 INT,
<<+ family B >>
C3 char(10)
C4 varchar(20)
)
In addition, prefixing the column name with a family name makes it look much
non-ANSI. Should we instead put the family definition to the attribute section
if the user prefers that way, such as
create table T
(
C1 int default null family abc,
C2 int default null family xyz,
)
Lastly, we probably should state that columns in a family will be stored
together, possibly in one set of HFILEs. Columns from two different families
will be stored separately.
> Add support for multiple column families in a trafodion table
> -------------------------------------------------------------
>
> Key: TRAFODION-1419
> URL: https://issues.apache.org/jira/browse/TRAFODION-1419
> Project: Apache Trafodion
> Issue Type: New Feature
> Reporter: Anoop Sharma
> Assignee: Anoop Sharma
>
> This proposal is to add support for multiple column families in trafodion
> tables. With this feature, one can store columns into multiple column
> families. One use for this would be to store frequently used columns in one
> column family and infrequently used columns to be stored in a different
> column family. That will have performance improvement when those columns are
> retrieved from hbase. There could be other uses as well.
> Syntax:
> create table <tablename> ( <colFam1>.<colName1> <datatype>,
> <colFam2>.<colName2> <datatype> ….)
> attributes default column family <colFam>;
> alter table <tablename> add column <colFam>.<colName> datatype;
> <colFam> : name of column family for that column
> Semantics:
> <colFam> name follows identifier rules. If not double quoted, then it
> will be upper cased. If double quoted, then case will be maintained.
> User specified column family can be of arbitrary length. To optimize
> space for column family stored in a cell, a 2 byte encoding is generated.
> Mapping of user specified column family to encoded column family is stored in
> metadata.
> If no column family is specified for a column during create table, then
> the family specified in ‘attributes default column family’ clause is used.
> If no ‘attribute default column family’ clause is specified , then system
> default col family is used.
> column family specification is supported for regular and volatile
> tables.
> all unique column families specified during create or alter are added
> to the table
> maximum number of column families supported in one table is 32. But it
> is hbase recommendation to not create too many column families.
> alter statement can be used to assign specific hbase options to
> specific column families
> using the NAME clause. If no name clause is specified, then alter hbase
> options are applied
> to all col families.
> invoke and showddl statements will show the original user specified
> column families and not the encoded column families
> Currently, multiple column families are not supported for columns of a
> user created or an implicitly created index.
> The default column family of the corresponding base table is used for all
> index columns.
> column family cannot be specified in a DML query
> column family cannot be specified for columns of an aligned row format
> table since all columns are stored as one cell
> Column names must be unique for each table. The same column name cannot
> be used as part of multiple column families.
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