WHy Flush Tables don't worK ? I can INSERT /SELECT into TABLE.
mysql> FLUSH TABLES;
Query OK, 0 rows affected (0.00 sec)
mysql> SELECT COUNT(*) FROM big_table;
+----------+
| COUNT(*) |
+----------+
| 1054155 |
+----------+
1 row in set (1.13 sec)
mysql> INSERT INTO exept VALUES(1);
Query OK, 1 row affected (0.02 sec)
I have all privileges.
When I use FLUSH TABLES WITH READ LOCK I can't insert but can select queries:
mysql> FLUSH TABLES WITH READ LOCK;
Query OK, 0 rows affected (0.00 sec)
mysql> INSERT INTO exept VALUES(1);
ERROR 1223 (HY000): Can't execute the query because you have a conflicting read lock
mysql> SELECT * FROM exept;
+----+
| id |
+----+
| 1 |
+----+
1 row in set (0.03 sec)
How disabled INSERT/SELECT queries ?
Related
I have table_a with and auto_increment column named id and string column named name.
Running the statement:
INSERT INTO table_a(id, name)VALUES(DEFAULT, 'test');
Results to (MySQL):
+----+------+
| id | name |
+----+------|
| 1 | test |
+----+------+
Running the similar statement in MariaDB results to:
+----+------+
| id | name |
+----+------|
| 0 | test |
+----+------+
Other scenario:
I tried editing the AUTO_INCREMENT value of the table to 30. MySQL inserts 30 while MariaDB inserts 0.
What is the difference of DEFAULT value in INSERT statement of MySQL and MariaDB? Is this a bug in MariaDB or it is working as intended?
This behavior is controlled by SQL_MODE='NO_AUTO_VALUE_ON_ZERO', both in MySQL and MariaDB. If you observe the difference, it's most likely because you have different sql_mode on the instances.
MariaDB [test]> CREATE TABLE t (id BIGINT(20) UNSIGNED NOT NULL AUTO_INCREMENT PRIMARY KEY);
Query OK, 0 rows affected (0.20 sec)
MariaDB [test]> SET SQL_MODE='';
Query OK, 0 rows affected (0.00 sec)
MariaDB [test]> INSERT INTO t (id) VALUES (DEFAULT);
Query OK, 1 row affected (0.05 sec)
MariaDB [test]> SELECT * FROM t;
+----+
| id |
+----+
| 1 |
+----+
1 row in set (0.00 sec)
MariaDB [test]> DROP TABLE t;
Query OK, 0 rows affected (0.14 sec)
MariaDB [test]> CREATE TABLE t (id BIGINT(20) UNSIGNED NOT NULL AUTO_INCREMENT PRIMARY KEY);
Query OK, 0 rows affected (0.30 sec)
MariaDB [test]> SET SQL_MODE='NO_AUTO_VALUE_ON_ZERO';
Query OK, 0 rows affected (0.00 sec)
MariaDB [test]> INSERT INTO t (id) VALUES (DEFAULT);
Query OK, 1 row affected (0.03 sec)
MariaDB [test]> SELECT * FROM t;
+----+
| id |
+----+
| 0 |
+----+
1 row in set (0.00 sec)
I have a project in which I insert a lot if info to a table with an auto increment primary key per second and do that with multi-threading which means that there are many threads that tries to insert a new row to that table. Because there is a lock on the table for insert queries, I cant perform inserts concurrently and therefore I cant get maximum performance from the threads...
Is there a way to overcome this lock?
You can set the innodb_autoinc_lock_mode to 1 in the my.cnf. Then there is no LOCK for Auto_increment. Then it is possible that you have holes in the Values if one Thead rollback an see sample
MariaDB [test]> show variables like 'innodb_autoinc_lock_mode';
+--------------------------+-------+
| Variable_name | Value |
+--------------------------+-------+
| innodb_autoinc_lock_mode | 1 |
+--------------------------+-------+
1 row in set (0.00 sec)
sample 1
MariaDB [test]> start transaction;
Query OK, 0 rows affected (0.00 sec)
MariaDB [test]> insert into autoinc VALUES(NULL,'hello');
Query OK, 1 row affected (0.01 sec)
thread 2 ------------------> MariaDB [test]> start transaction;
thread 2 ------------------> Query OK, 0 rows affected (0.00 sec)
thread 2 ------------------> MariaDB [test]> insert into autoinc VALUES(NULL,'world');
thread 2 ------------------> Query OK, 1 row affected (0.00 sec)
thread 2 ------------------> MariaDB [test]> commit;
thread 2 ------------------> Query OK, 0 rows affected (0.00 sec)
thread 2 ------------------> MariaDB [test]>
MariaDB [test]> commit;
Query OK, 0 rows affected (0.00 sec)
MariaDB [test]> select * from autoinc;
+----+-------+
| id | d |
+----+-------+
| 1 | hello |
| 2 | world |
+----+-------+
2 rows in set (0.00 sec)
MariaDB [test]>
sample 2 with rollback
MariaDB [test]> start transaction;
Query OK, 0 rows affected (0.00 sec)
MariaDB [test]> insert into autoinc VALUES(NULL,'Guten');
Query OK, 1 row affected (0.00 sec)
thread 2 ------------------> MariaDB [test]> start transaction;
thread 2 ------------------> Query OK, 0 rows affected (0.00 sec)
thread 2 ------------------> MariaDB [test]> insert into autoinc VALUES(NULL,'Tag');
thread 2 ------------------> Query OK, 1 row affected (0.00 sec)
thread 2 ------------------> MariaDB [test]> commit;
thread 2 ------------------> Query OK, 0 rows affected (0.01 sec)
MariaDB [test]> rollback;
Query OK, 0 rows affected (0.00 sec)
MariaDB [test]> select * from autoinc;
+----+-------+
| id | d |
+----+-------+
| 1 | hello |
| 2 | world |
| 4 | Tag |
+----+-------+
3 rows in set (0.00 sec)
MariaDB [test]>
When I use CREATE TABLE tbl_name I can only specify a table in database I currently use.
Is there any way to CREATE TABLE tbl_name in database1 without a prior USE database1?
Try:
mysql> CREATE DATABASE `test_1`;
Query OK, 1 row affected (0.00 sec)
mysql> CREATE DATABASE `test_2`;
Query OK, 1 row affected (0.00 sec)
mysql> SELECT DATABASE();
+------------+
| DATABASE() |
+------------+
| NULL |
+------------+
1 row in set (0.00 sec)
mysql> CREATE TABLE `test_1`.`table_1` (`column_1` BOOL);
Query OK, 0 rows affected (0.00 sec)
mysql> CREATE TABLE `test_2`.`table_2` (`column_1` BOOL);
Query OK, 0 rows affected (0.01 sec)
mysql> USE `test_1`;
Database changed
mysql> SHOW TABLES;
+------------------+
| Tables_in_test_1 |
+------------------+
| table_1 |
+------------------+
1 row in set (0.00 sec)
mysql> USE `test_2`;
Database changed
mysql> SHOW TABLES;
+------------------+
| Tables_in_test_2 |
+------------------+
| table_2 |
+------------------+
1 row in set (0.00 sec)
I think I read that the delete trigger doesn't know what data was deleted and loops over the whole table applying the trigger. Is that true?
Does that mean that the before delete loops over the whole table before the data is deleted and after delete loops over the whole table after the delete occurs?
Is there no way to loop over just the deleted records? So If 10 records are deleted loop over them?
DELIMITER $$
DROP TRIGGER `before_delete_jecki_triggername`$$
CREATE TRIGGER before_delete_triggername
BEFORE DELETE ON table
FOR EACH ROW
BEGIN
/*do stuff*/
END$$
DELIMITER ;
Thanks,
Mat
I think it was due to a confusion with FOR EACH ROW statement.
It is only for "matched records for the statement issued before trigger is invoked."
If there exists N number of records in a table and matches records for where id=x,
assuming x causes a result of less than N records, say N-5, then
FOR EACH ROW causes a loop for N-5 times only.
UPDATE:
A sample test run on the rows affected due to FOR EACH ROW statement is shown below.
mysql> -- create a test table
mysql> drop table if exists tbl; create table tbl ( i int, v varchar(10) );
Query OK, 0 rows affected (0.01 sec)
Query OK, 0 rows affected (0.06 sec)
mysql> -- set test data
mysql> insert into tbl values(1,'one'),(2,'two' ),(3,'three'),(10,'ten'),(11,'eleven');
Query OK, 5 rows affected (0.02 sec)
Records: 5 Duplicates: 0 Warnings: 0
mysql> select * from tbl;
+------+--------+
| i | v |
+------+--------+
| 1 | one |
| 2 | two |
| 3 | three |
| 10 | ten |
| 11 | eleven |
+------+--------+
5 rows in set (0.02 sec)
mysql> select count(*) row_count from tbl;
+-----------+
| row_count |
+-----------+
| 5 |
+-----------+
1 row in set (0.00 sec)
mysql>
mysql> -- record loop count of trigger in a table
mysql> drop table if exists rows_affected; create table rows_affected( i int );
Query OK, 0 rows affected (0.02 sec)
Query OK, 0 rows affected (0.05 sec)
mysql> select count(*) 'rows_affected' from rows_affected;
+---------------+
| rows_affected |
+---------------+
| 0 |
+---------------+
1 row in set (0.00 sec)
mysql>
mysql> set #cnt=0;
Query OK, 0 rows affected (0.00 sec)
mysql>
mysql> -- drop trigger if exists trig_bef_del_on_tbl;
mysql> delimiter //
mysql> create trigger trig_bef_del_on_tbl before delete on tbl
-> for each row begin
-> set #cnt = if(#cnt is null, 1, (#cnt+1));
->
-> /* for cross checking save loop count */
-> insert into rows_affected values ( #cnt );
-> end;
-> //
Query OK, 0 rows affected (0.00 sec)
mysql>
mysql> delimiter ;
mysql>
mysql> -- now let us test the delete operation
mysql> delete from tbl where i like '%1%';
Query OK, 3 rows affected (0.02 sec)
mysql>
mysql> -- now let us see what the loop count was
mysql> select #cnt as 'cnt';
+------+
| cnt |
+------+
| 3 |
+------+
1 row in set (0.00 sec)
mysql>
mysql> -- now let us see the table data
mysql> select * from tbl;
+------+-------+
| i | v |
+------+-------+
| 2 | two |
| 3 | three |
+------+-------+
2 rows in set (0.00 sec)
mysql> select count(*) row_count from tbl;
+-----------+
| row_count |
+-----------+
| 2 |
+-----------+
1 row in set (0.00 sec)
mysql> select count(*) 'rows_affected' from rows_affected;
+---------------+
| rows_affected |
+---------------+
| 3 |
+---------------+
1 row in set (0.00 sec)
mysql>
Can there any way to insert a hex value into MYSQL?
I also want to be able to retreive it in hex form.
For example, something like:
INSERT INTO table ( hexTag )
VALUES ( HEX(0x41) );
And if I do this, I want it to put an 'A' into the table
For that particular use case, you can either insert the hex value directly and it will be interpreted as a string, or use HEX() to input and UNHEX() to output
mysql> create table hexTable(pseudoHex varchar(50));
Query OK, 0 rows affected (0.01 sec)
mysql> insert into hexTable values (0x41);
Query OK, 1 row affected (0.00 sec)
mysql> select * from hexTable;
+-----------+
| pseudoHex |
+-----------+
| A |
+-----------+
1 row in set (0.00 sec)
mysql> select HEX(pseudoHex) from hexTable;
+----------------+
| HEX(pseudoHex) |
+----------------+
| 41 |
+----------------+
1 row in set (0.00 sec)
mysql> delete from hexTable;
Query OK, 1 row affected (0.00 sec)
mysql> insert into hexTable values (HEX('A'));
Query OK, 1 row affected (0.00 sec)
mysql> select UNHEX(pseudoHex) from hexTable;
+------------------+
| UNHEX(pseudoHex) |
+------------------+
| A |
+------------------+
1 row in set (0.00 sec)
mysql> select * from hexTable;
+-----------+
| pseudoHex |
+-----------+
| 41 |
+-----------+
1 row in set (0.00 sec)
See these links.