In the last episode (Oct 16), Kailash R said:
> Nice input Dan. Let me run some checks. My query is as follows:
>
> select group_concat(Field1), field2, field3 from table1 group by field2,
> field3 into str;
> @sql = concat("select blah ... where field1 in ' ,str);
> prepare stmt from @sql;
> execute stmt;
> deallocate prepare stmt;
Did you maybe get a warning on your first SELECT statement? On a test table
of dictionary words:
mysql> select group_concat(word) from words into @a;
Query OK, 1 row affected, 1 warning (0.70 sec)
mysql> show warnings;
+---------+------+-----------------------------------+
| Level | Code | Message |
+---------+------+-----------------------------------+
| Warning | 1260 | Row 146 was cut by GROUP_CONCAT() |
+---------+------+-----------------------------------+
1 row in set (0.00 sec)
mysql> select length(@a);
+------------+
| length(@a) |
+------------+
| 1024 |
+------------+
1 row in set (0.01 sec)
>From the documentation, GROUP_CONCAT has a default 1024-byte limit:
http://dev.mysql.com/doc/refman/5.5/en/group-by-functions.html#function_group-concat
The result is truncated to the maximum length that is given by the
group_concat_max_len system variable, which has a default value of 1024.
The value can be set higher, although the effective maximum length of
the return value is constrained by the value of max_allowed_packet. The
syntax to change the value of group_concat_max_len at runtime is as
follows, where val is an unsigned integer:
SET [GLOBAL | SESSION] group_concat_max_len = val;
--
Dan Nelson
dnel...@allantgroup.com
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