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MDEV-39179: Incorrect NULL handling in UPDATE ... RETURNING result

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Analysis:
OLD_VALUE() swapped only field->ptr, leaving null_ptr pointing to the
current record. This caused incorrect NULL results.

Fix:
Store null_ptr_old for record[1] and swap it together with ptr to
preserve correct NULL semantics.
This commit is contained in:
Rucha Deodhar
2026-04-14 17:11:46 -04:00
parent 85e4f5cfb3
commit 9b325e1b7d
9 changed files with 57 additions and 10 deletions
Download Patch File Download Diff File Expand all files Collapse all files

11
mysql-test/main/update.result
View File

@@ -1137,4 +1137,15 @@ UPDATE t3 SET a = 10 RETURNING OLD_VALUE(a) AS old_value;
old_value
1
DROP TABLE t3;
#
# MDEV-39179: Incorrect NULL handling in UPDATE ... RETURNING result
#
CREATE OR REPLACE TABLE t1(a VARCHAR(10));
INSERT INTO t1 VALUES('') RETURNING *;
a
UPDATE t1 SET a=NULL RETURNING OLD_VALUE(a) AS old, a AS new;
old new
NULL
DROP TABLE t1;
# End of 13.0 test

10
mysql-test/main/update.test
View File

@@ -995,4 +995,14 @@ UPDATE t3 SET a = 10 RETURNING OLD_VALUE(a) AS old_value;
DROP TABLE t3;
--echo #
--echo # MDEV-39179: Incorrect NULL handling in UPDATE ... RETURNING result
--echo #
CREATE OR REPLACE TABLE t1(a VARCHAR(10));
INSERT INTO t1 VALUES('') RETURNING *;
UPDATE t1 SET a=NULL RETURNING OLD_VALUE(a) AS old, a AS new;
DROP TABLE t1;
--echo # End of 13.0 test

4
sql/field.cc
View File

@@ -1934,8 +1934,8 @@ String *Field::val_int_as_str(String *val_buffer, bool unsigned_val)
Field::Field(uchar *ptr_arg,uint32 length_arg,uchar *null_ptr_arg,
uchar null_bit_arg,
utype unireg_check_arg, const LEX_CSTRING *field_name_arg)
:ptr(ptr_arg),
null_ptr(null_ptr_arg), table(0), orig_table(0),
:ptr(ptr_arg), ptr_old(nullptr),
null_ptr(null_ptr_arg), null_ptr_old(nullptr), table(0), orig_table(0),
table_name(0), field_name(*field_name_arg), option_list(0),
option_struct(0), key_start(0), part_of_key(0),
part_of_key_not_clustered(0), vcol_direct_part_of_key(0), part_of_sortkey(0),

2
sql/field.h
View File

@@ -809,8 +809,10 @@ public:
/**
Byte where the @c NULL bit is stored inside a record. If this Field is a
@c NOT @c NULL field, this member is @c NULL.
null_ptr_old points to old field.
*/
uchar *null_ptr;
uchar *null_ptr_old;
/*
Note that you can use table->in_use as replacement for current_thd member
only inside of val_*() and store() members (e.g. you can't use it in cons)

20
sql/item.cc
View File

@@ -7966,13 +7966,19 @@ bool Item_old_field::send(Protocol *protocol, st_value *buffer)
{
bool result;
std::swap(field->ptr_old, field->ptr);
change_field_ptr();
result= Item_field::send(protocol, buffer);
std::swap(field->ptr_old, field->ptr);
change_field_ptr();
return result;
}
void Item_old_field::change_field_ptr()
{
std::swap(field->ptr_old, field->ptr);
std::swap(field->null_ptr, field->null_ptr_old);
}
bool Item_old_field::fix_fields(THD *thd, Item **reference)
{
@@ -7985,6 +7991,16 @@ bool Item_old_field::fix_fields(THD *thd, Item **reference)
{
field->ptr_old= field->table->record[1] +
field->offset(field->table->record[0]);
if (field->null_ptr)
{
field->null_ptr_old =
field->table->record[1] +
(field->null_ptr - field->table->record[0]);
}
else
{
field->null_ptr_old = nullptr;
}
}
else
{

1
sql/item.h
View File

@@ -4114,6 +4114,7 @@ public:
bool send(Protocol *protocol, st_value *buffer) override;
Type type() const override { return FIELD_OLD_ITEM; }
bool fix_fields(THD *, Item **) override;
void change_field_ptr();
private:
uchar *saved_row_ref;

15
sql/sql_update.cc
View File

@@ -391,6 +391,7 @@ bool Sql_cmd_update::update_single_table(THD *thd)
Explain_update *explain;
query_plan.index= MAX_KEY;
query_plan.using_filesort= FALSE;
bool record_was_same, need_update, trg_skip_row;
// For System Versioning (may need to insert new fields to a table).
ha_rows rows_inserted= 0;
@@ -977,7 +978,7 @@ update_begin:
if (unlikely(returning_result->send_result_set_metadata(
thd->lex->returning()->returning_list,
Protocol::SEND_NUM_ROWS | Protocol::SEND_EOF)))
error= 1;
goto error;
}
while (!(error=info.read_record()) && !thd->killed)
@@ -996,7 +997,7 @@ update_begin:
cut_fields_for_portion_of_time(thd, table,
table_list->period_conditions);
bool trg_skip_row= false;
trg_skip_row= false;
if (fill_record_n_invoke_before_triggers(thd, table, *fields, *values, 0,
TRG_EVENT_UPDATE,
&trg_skip_row))
@@ -1011,8 +1012,8 @@ update_begin:
found++;
bool record_was_same= false;
bool need_update= !can_compare_record || compare_record(table);
record_was_same= false;
need_update= !can_compare_record || compare_record(table);
if (need_update)
{
@@ -3262,7 +3263,10 @@ bool Sql_cmd_update::execute_inner(THD *thd)
/* This is UPDATE ... RETURNING. It will return output to the client */
if (thd->lex->analyze_stmt)
{
returning_result= new (thd->mem_root) select_send_analyze(thd);
if (!(returning_result= new (thd->mem_root) select_send_analyze(thd)))
{
return true;
}
save_protocol= thd->protocol;
thd->protocol= new Protocol_discard(thd);
}
@@ -3294,6 +3298,7 @@ bool Sql_cmd_update::execute_inner(THD *thd)
{
delete thd->protocol;
thd->protocol= save_protocol;
save_protocol= nullptr;
}
if (unlikely(res))
{

2
sql/sql_update.h
View File

@@ -48,7 +48,7 @@ public:
ha_rows found{0}, updated{0};
Sql_cmd_update(bool multitable_arg)
: orig_multitable(multitable_arg), multitable(multitable_arg),
save_protocol(nullptr)
returning_result(nullptr), save_protocol(nullptr)
{}
enum_sql_command sql_command_code() const override

2
sql/sql_yacc.yy
View File

@@ -9935,6 +9935,7 @@ expr:
lex->sql_command == SQLCOM_UPDATE_MULTI))
{
my_error(ER_WRONG_USAGE, MYF(0), "OLD_VALUE", "non-UPDATE");
MYSQL_YYABORT;
}
$$= new (thd->mem_root)
Item_old_field(thd,
@@ -14583,6 +14584,7 @@ opt_returning:
{
my_error(ER_NOT_SUPPORTED_YET, MYF(0),
"RETURNING for multi-table UPDATE");
MYSQL_YYABORT;
}
/*