NULL values when there is no DEFAULT
Copy and inplace algorithm works similarly for
NULL to NOT NULL conversion for the following cases:
(1) strict sql mode - Should give error.
(2) non-strict sql mode - Should give warnings alone
(3) alter ignore table command. - Should give warnings alone.
- Allow NOT NULL constraint to replace the NULL value in the row with
explicit or implicit default value.
- If the default value is non-const value then inplace alter won't
support it.
- ALTER IGNORE will ignore the error if the concurrent DML contains
NULL value.
When it comes to DEFAULT values of columns, InnoDB is imposing both
unnecessary and insufficient conditions on whether ALGORITHM=INPLACE
should be allowed for ALTER TABLE.
When changing an existing column to NOT NULL, any NULL values in the
columns only get a special treatment if the column is changed to an
AUTO_INCREMENT column (which is not supported by ALGORITHM=INPLACE)
or the column type is TIMESTAMP. In all other cases, an error
must be reported for the failure to convert a NULL value to NOT NULL.
InnoDB was unnecessarily interested in whether the DEFAULT value
is not constant when altering other than TIMESTAMP columns. Also,
when changing a TIMESTAMP column to NOT NULL, InnoDB was performing
an insufficient check, and it was incorrectly allowing a constant
DEFAULT value while not being able to replace NULL values with that
constant value.
Furthermore, in ADD COLUMN, InnoDB is unnecessarily rejecting certain
nondeterministic DEFAULT expressions (depending on the session
parameters or the current time).
ha_innobase::check_if_supported_inplace_alter(): For now, reject
ALGORITHM=INPLACE when a non-constant DEFAULT expression is specified
for ADD COLUMN or for changing a NULL column to NOT NULL.
Later, we should evaluate the non-constant column values in these cases.
Analysis; Problem is that InnoDB does not have support for generating
CURRENT_TIMESTAMP or constant default.
Fix: Add additional check if column has changed from NULL -> NOT NULL
and column default has changed. If this is is first column definition
whose SQL type is TIMESTAMP and it is defined as NOT NULL and
it has either constant default or function default we must use
"Copy" method for alter table.
