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Bug#26020: User-Defined Variables are not consistent with

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columns data types

The "SELECT @lastId, @lastId := Id FROM t" query returns
different result sets depending on the type of the Id column
(INT or BIGINT).

Note: this fix doesn't cover the case when a select query
references an user variable and stored function that
updates a value of that variable, in this case a result
is indeterminate.


The server uses incorrect assumption about a constantness of
an user variable value as a select list item: 

The server caches a last query number where that variable
was changed and compares this number with a current query
number. If these numbers are different, the server guesses,
that the variable is not updating in the current query, so
a respective select list item is a constant. However, in some
common cases the server updates cached query number too late.


The server has been modified to memorize user variable
assignments during the parse phase to take them into account
on the next (query preparation) phase independently of the
order of user variable references/assignments in a select
item list.
This commit is contained in:
Gleb Shchepa 2008-09-18 13:38:44 +05:00
commit db1d38c910
8 changed files with 107 additions and 12 deletions
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15
sql/item_func.h
View file

@ -1294,6 +1294,17 @@ class Item_func_set_user_var :public Item_func
{
enum Item_result cached_result_type;
user_var_entry *entry;
/*
The entry_thd variable is used:
1) to skip unnecessary updates of the entry field (see above);
2) to reset the entry field that was initialized in the other thread
(for example, an item tree of a trigger that updates user variables
may be shared between several connections, and the entry_thd field
prevents updates of one connection user variables from a concurrent
connection calling the same trigger that initially updated some
user variable it the first connection context).
*/
THD *entry_thd;
char buffer[MAX_FIELD_WIDTH];
String value;
my_decimal decimal_buff;
@ -1309,7 +1320,8 @@ class Item_func_set_user_var :public Item_func
public:
LEX_STRING name; // keep it public
Item_func_set_user_var(LEX_STRING a,Item *b)
:Item_func(b), cached_result_type(INT_RESULT), name(a)
:Item_func(b), cached_result_type(INT_RESULT),
entry(NULL), entry_thd(NULL), name(a)
{}
enum Functype functype() const { return SUSERVAR_FUNC; }
double val_real();
@ -1340,6 +1352,7 @@ public:
}
void save_org_in_field(Field *field) { (void)save_in_field(field, 1, 0); }
bool register_field_in_read_map(uchar *arg);
bool set_entry(THD *thd, bool create_if_not_exists);
};