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This change takes into account a column's GENERATED ALWAYS AS
expression dependcy on sql_mode's PAD_CHAR_TO_FULL_LENGTH and
NO_UNSIGNED_SUBTRACTION flags.
Indexed virtual columns as well as persistent generated columns are
now not allowed to have such dependencies to avoid inconsistent data
or index files on sql_mode changes.
So an error is now returned in cases like this:
CREATE OR REPLACE TABLE t1
(
a CHAR(5),
v VARCHAR(5) AS (a) PERSISTENT -- CHAR->VARCHAR or CHAR->TEXT = ERROR
);
Functions RPAD() and RTRIM() can now remove dependency on
PAD_CHAR_TO_FULL_LENGTH. So this can be used instead:
CREATE OR REPLACE TABLE t1
(
a CHAR(5),
v VARCHAR(5) AS (RTRIM(a)) PERSISTENT
);
Note, unlike CHAR->VARCHAR and CHAR->TEXT this still works,
not RPAD(a) is needed:
CREATE OR REPLACE TABLE t1
(
a CHAR(5),
v CHAR(5) AS (a) PERSISTENT -- CHAR->CHAR is OK
);
More sql_mode flags may affect values of generated columns.
They will be addressed separately.
See comments in sql_mode.h for implementation details.
162 lines
6.6 KiB
C++
162 lines
6.6 KiB
C++
#ifndef SQL_MODE_H_INCLUDED
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#define SQL_MODE_H_INCLUDED
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/*
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Copyright (c) 2019, MariaDB.
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This program is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; version 2 of the License.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program; if not, write to the Free Software
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Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1335 USA */
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#ifdef USE_PRAGMA_INTERFACE
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#pragma interface /* gcc class implementation */
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#endif
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#include "sql_basic_types.h"
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/*
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class Sql_mode_dependency
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A combination of hard and soft dependency on sql_mode.
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Used to watch if a GENERATED ALWAYS AS expression guarantees consitent
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data written to its virtual column.
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A virtual column can appear in an index if:
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- the generation expression does not depend on any sql_mode flags, or
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- the generation expression has a soft dependency on an sql_mode flag,
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and the column knows how to handle this dependeny.
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A virtual column cannot appear in an index if:
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- its generation expression has a hard dependency
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- its generation expression has a soft dependency, but the column
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cannot handle it on store.
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An error is reported in such cases.
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How dependencies appear:
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- When a column return value depends on some sql_mode flag,
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its Item_field adds a corresponding bit to m_soft. For example,
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Item_field for a CHAR(N) column adds the PAD_CHAR_TO_FULL_LENGTH flag.
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- When an SQL function/operator return value depends on some sql_mode flag,
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it adds a corresponding bit to m_soft. For example, Item_func_minus
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adds the MODE_NO_UNSIGNED_SUBTRACTION in case of unsigned arguments.
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How dependency are processed (see examples below):
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- All SQL functions/operators bit-OR all hard dependencies from all arguments.
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- Some soft dependencies can be handled by the underlying Field on store,
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e.g. CHAR(N) can handle PAD_CHAR_TO_FULL_LENGTH.
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- Some soft dependencies can be handled by SQL functions and operators,
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e.g. RTRIM(expr) removes expr's soft dependency on PAD_CHAR_TO_FULL_LENGTH.
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If a function or operator handles a soft dependency on a certain sql_mode
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flag, it removes the corresponding bit from m_soft (see below).
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Note, m_hard is not touched in such cases.
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- When an expression with a soft dependency on a certain sql_mode flag
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goes as an argument to an SQL function/operator which cannot handle
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this flag, the dependency escalates from soft to hard
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(by moving the corresponding bit from m_soft to m_hard) and cannot be
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handled any more on the upper level, neither by a Field on store,
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nor by another SQL function/operator.
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There are four kinds of Items:
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1. Items that generate a soft or hard dependency, e.g.
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- Item_field for CHAR(N) - generates soft/PAD_CHAR_TO_FULL_LENGTH
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- Item_func_minus - generates soft/NO_UNSIGNED_SUBTRACTION
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2. Items that convert a soft dependency to a hard dependency.
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This happens e.g. when an Item_func instance gets a soft dependency
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from its arguments, and it does not know how to handle this dependency.
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Most Item_func descendants do this.
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3. Items that remove soft dependencies, e.g.:
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- Item_func_rtrim - removes soft/PAD_CHAR_TO_FULL_LENGTH
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that came from args[0] (under certain conditions)
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- Item_func_rpad - removes soft/PAD_CJAR_TO_FULL_LENGTH
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that came from args[0] (under certain conditions)
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4. Items that repeat soft dependency from its arguments to the caller.
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They are not implemented yet. But functions like Item_func_coalesce,
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Item_func_case, Item_func_case_abbreviation2 could do this.
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Examples:
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1. CREATE OR REPLACE TABLE t1 (a CHAR(5), v CHAR(20) AS(a), KEY(v));
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Here `v` has a soft dependency on `a`.
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The value of `a` depends on PAD_CHAR_TO_FULL_LENGTH, it can return:
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- 'a' - if PAD_CHAR_TO_FULL_LENGTH is disabled
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- 'a' followed by four spaces - if PAD_CHAR_TO_FULL_LENGTH is enabled
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But `v` will pad trailing spaces to the full length on store anyway.
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So Field_string handles this soft dependency on store.
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This combination of the virtial column data type and its generation
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expression is safe and provides consistent data in `v`, which is
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'a' followed by four spaces, no matter what PAD_CHAR_TO_FULL_LENGTH is.
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2. CREATE OR REPLACE TABLE t1 (a CHAR(5), v VARCHAR(20) AS(a), KEY(v));
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Here `v` has a soft dependency on `a`. But Field_varstring does
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not pad spaces on store, so it cannot handle this dependency.
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This combination of the virtual column data type and its generation
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expression is not safe. An error is returned.
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3. CREATE OR REPLACE TABLE t1 (a CHAR(5), v INT AS(LENGTH(a)), KEY(v));
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Here `v` has a hard dependency on `a`, because the value of `a`
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is wrapped to the function LENGTH().
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The value of `LENGTH(a)` depends on PAD_CHAR_TO_FULL_LENGTH, it can return:
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- 1 - if PAD_CHAR_TO_FULL_LENGTH is disabled
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- 4 - if PAD_CHAR_TO_FULL_LENGTH is enabled
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This combination cannot provide consistent data stored to `v`,
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therefore it's disallowed.
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*/
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class Sql_mode_dependency
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{
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sql_mode_t m_hard;
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sql_mode_t m_soft;
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public:
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Sql_mode_dependency()
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:m_hard(0), m_soft(0)
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{ }
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Sql_mode_dependency(sql_mode_t hard, sql_mode_t soft)
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:m_hard(hard), m_soft(soft)
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{ }
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sql_mode_t hard() const { return m_hard; }
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sql_mode_t soft() const { return m_soft; }
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operator bool () const
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{
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return m_hard > 0 || m_soft > 0;
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}
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Sql_mode_dependency operator|(const Sql_mode_dependency &other) const
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{
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return Sql_mode_dependency(m_hard | other.m_hard, m_soft | other.m_soft);
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}
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Sql_mode_dependency operator&(const Sql_mode_dependency &other) const
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{
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return Sql_mode_dependency(m_hard & other.m_hard, m_soft & other.m_soft);
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}
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Sql_mode_dependency &operator|=(const Sql_mode_dependency &other)
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{
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m_hard|= other.m_hard;
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m_soft|= other.m_soft;
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return *this;
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}
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Sql_mode_dependency &operator&=(const Sql_mode_dependency &other)
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{
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m_hard&= other.m_hard;
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m_soft&= other.m_soft;
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return *this;
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}
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Sql_mode_dependency &soft_to_hard()
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{
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m_hard|= m_soft;
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m_soft= 0;
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return *this;
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}
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void push_dependency_warnings(THD *thd);
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};
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#endif // SQL_MODE_H_INCLUDED
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