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This patch implements basic IDENTITY feature, with the following
syntax:
<col> GENERATED {ALWAYS AS | BY DEFAULT [ON NULL]} identity_props
The following identity_props are acknowleged:
- START WITH num - Supported, only positive values
- INCREMENT BY num - Supported, only positive values
- MAXVALUE num - Supported, only positive values. Engine treating may
vary.
The following identity_props are recognized and saved in
the table metadata, but ignored
- ORDER
- CYCLE
- MINVALUE num
The following identity_props are recognized and fully ignored at the
parser level.
These properties are newly added keywords, however they are not
reserved, i.e. can be used as identifiers, column names, etc. just as
before:
- KEEP
- SCALE
- SHARD
- EXTEND
- NOKEEP
- NOSCALE
- NOSHARD
- NOEXTEND
The patch is designed in minimalistic manner, re-using existing
AUTO_INCREMENT implementation, yet utilizing the default values
evaluation mechanism. As a result, it grants usage of CHECK constraints
and other table expressions: vcols, default values with identity column.
Some notes:
* IDENTITY is evaluated as Field's default_value. Even GENERATED ALWAYS
is considered "default", since the IDENTITY expression is not
determistic.
* However, the GENERATED ALWAYS kind cannot be assigned in DMLs in
STRICT SQL_MODE. That is, the behavior for users is like other GENERATED
ALWAYS columns.
* It honors INSERT_ID and uses it.
* IDENTITY column is always replicated and saved in mariadb-dump, which
is guaranteed by using default_value instead of vcol_expr (vcols, even
stored, are usually not replicated)
* In frm, it is loaded and saved as a default expression. For that,
parse_vcol_expr definition was extended to support things like GENERATED
BY DEFAULT, and even GENERATED ALWAYS. That is, no EXTRA2 header had to
be added.
* struct Autoinc_spec is stored in Item_dentity_next, so table
structures are preserved as they were.
* New IDENTITY keyword is not reserved
Known issues:
* LAST_INSERT_ID() is not working for now.
* update t set col=default(identity_column) is broken, as reported in
MDEV-31854 for nextval.
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