English is not my native language; please excuse typing errors.
Im using 5.5.38-MariaDB.
Mysql statement：
SELECT CAST(11111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111
AS char);
I get result is 99999999999999999999999999999999999999999999999999999999999999999,why?
Update:
MariaDB [(none)]> SELECT CAST(199999999999999999999999999999999999999999999999999999999999999999999999999999999 AS char);
+-------------------------------------------------------------------------------------------------+
| CAST(199999999999999999999999999999999999999999999999999999999999999999999999999999999 AS char) |
+-------------------------------------------------------------------------------------------------+
| 199999999999999999999999999999999999999999999999999999999999999999999999999999999 |
+-------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)
MariaDB [(none)]> SELECT CAST(1999999999999999999999999999999999999999999999999999999999999999999999999999999999 AS char);
+--------------------------------------------------------------------------------------------------+
| CAST(1999999999999999999999999999999999999999999999999999999999999999999999999999999999 AS char) |
+--------------------------------------------------------------------------------------------------+
| 99999999999999999999999999999999999999999999999999999999999999999 |
+--------------------------------------------------------------------------------------------------+
1 row in set, 1 warning (0.01 sec)
MariaDB [(none)]> SHOW WARNINGS;
+---------+------+--------------------------------------------------------------+
| Level | Code | Message |
+---------+------+--------------------------------------------------------------+
| Warning | 1916 | Got overflow when converting '' to DECIMAL. Value truncated. |
+---------+------+--------------------------------------------------------------+
1 row in set (0.00 sec)
The 1111... is parsed as a number, specifically as DECIMAL(65, ...). 65 is the max; since the thing is bigger than that, it gave you 65 9's. And it gave you a warning (that was probably ignored):
mysql> SELECT CAST(11111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111 AS CHAR) AS too_big;
+-------------------------------------------------------------------+
| too_big |
+-------------------------------------------------------------------+
| 99999999999999999999999999999999999999999999999999999999999999999 |
+-------------------------------------------------------------------+
1 row in set, 1 warning (0.00 sec)
mysql> SHOW WARNINGS;
+---------+------+---------------------------------------+
| Level | Code | Message |
+---------+------+---------------------------------------+
| Warning | 1292 | Truncated incorrect DECIMAL value: '' |
+---------+------+---------------------------------------+
1 row in set (0.00 sec)
What were you hoping to get?
Related
I need your help. I am trying to transform a text field (containing: 2020-09-11T08:32:50Z) into a date field. I have tried with TIMESTAMP statement and I get the warning: 1292 Truncated incorrect datetime value.
I have also tried with STR_TO_DATE statement and I get another warning: 1411 Incorrect datetime value.
I have entered SET ##SESSION.sql_mode='ALLOW_INVALID_DATES' to avoid some configuration error, but the error remains.
Thanks a lot!
MySQL understands the format up to the 'Z'. If you remove the 'Z' it will work fine.
Demo:
mysql> select date('2020-09-11T08:32:50Z');
+------------------------------+
| date('2020-09-11T08:32:50Z') |
+------------------------------+
| 2020-09-11 |
+------------------------------+
1 row in set, 1 warning (0.01 sec)
mysql> show warnings;
+---------+------+------------------------------------------------------------+
| Level | Code | Message |
+---------+------+------------------------------------------------------------+
| Warning | 1292 | Truncated incorrect datetime value: '2020-09-11T08:32:50Z' |
+---------+------+------------------------------------------------------------+
1 row in set (0.00 sec)
mysql> select date('2020-09-11T08:32:50');
+-----------------------------+
| date('2020-09-11T08:32:50') |
+-----------------------------+
| 2020-09-11 |
+-----------------------------+
1 row in set (0.00 sec)
No warning is returned if the 'Z' is removed.
I have a table that has nullable columns:
+-------+--------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+--------------+------+-----+---------+-------+
| id | int(11) | YES | | NULL | |
| name | varchar(255) | YES | | NULL | |
+-------+--------------+------+-----+---------+-------+
I insert a row with name set to NULL;
INSERT INTO some_table (id, name) VALUES (1, NULL);
Query OK, 1 row affected (0.02 sec)
SELECT * FROM some_table;
+------+------+
| id | name |
+------+------+
| 1 | NULL |
+------+------+
1 row in set (0.01 sec)
If I alter the table's name column to be not-nullable it apparently converts NULL to an empty string:
ALTER TABLE some_table CHANGE COLUMN name name VARCHAR(255) NOT NULL;
Query OK, 1 row affected, 1 warning (0.02 sec)
Records: 1 Duplicates: 0 Warnings: 1
SELECT * FROM some_table;
+------+------+
| id | name |
+------+------+
| 1 | |
+------+------+
1 row in set (0.02 sec)
At this point I would expect an exception to be raised telling me that I have NULL in my dataset and I can not set the column name to NOT NULL.
Is this a configurable option in SQL/MariaDB?
Why is NULL being converted to an empty string?
There is a warning being invoked when altering the table:
SHOW WARNINGS;
+---------+------+-------------------------------------------+
| Level | Code | Message |
+---------+------+-------------------------------------------+
| Warning | 1265 | Data truncated for column 'name' at row 1 |
+---------+------+-------------------------------------------+
1 row in set (0.01 sec)
Version:
SELECT version();
+----------------+
| version() |
+----------------+
| 5.5.62-MariaDB |
+----------------+
1 row in set (0.02 sec)
Apparently, from the documentation for ALTER TABLE, enabling strict mode would prevent your alter statement from succeeding:
This conversion may result in alteration of data. For example, if you shorten a string column, values may be truncated. To prevent the operation from succeeding if conversions to the new data type would result in loss of data, enable strict SQL mode before using ALTER TABLE.
One way to enable strict mode from within MySQL:
SET GLOBAL sql_mode='STRICT_TRANS_TABLES';
See here for other options.
Using 10.3.15-MariaDB-1 on Debian Buster, I cannot reproduce the problem:
MariaDB [foo]> CREATE TABLE some_table(id int(11), name varchar(255));
Query OK, 0 rows affected (0.009 sec)
MariaDB [foo]> INSERT INTO some_table (id, name) VALUES (1, NULL);
Query OK, 1 row affected (0.003 sec)
MariaDB [foo]> SELECT * FROM some_table;
+------+------+
| id | name |
+------+------+
| 1 | NULL |
+------+------+
1 row in set (0.000 sec)
MariaDB [foo]> ALTER TABLE some_table CHANGE COLUMN name name VARCHAR(255) NOT NULL;
ERROR 1265 (01000): Data truncated for column 'name' at row 1
MariaDB [foo]> SELECT * FROM some_table;
+------+------+
| id | name |
+------+------+
| 1 | NULL |
+------+------+
1 row in set (0.000 sec)
MariaDB [foo]> SELECT version();
+-------------------+
| version() |
+-------------------+
| 10.3.15-MariaDB-1 |
+-------------------+
1 row in set (0.000 sec)
If possible, I suggest you update your MariaDB version. It seems very old to me.
DATE field type has limitations '1000-01-01' -'9999-12-31'.
BUT Why inserted '987-10-10' not '1000-01-01' ?
mysql> INSERT INTO DATE12(datas) VALUES('987-10-10');
Query OK, 1 row affected (0.03 sec)
mysql> SELECT * FROM DATE12;
+------+------------+
| id | datas |
+------+------------+
| NULL | 1987-11-04 |
| NULL | 0987-10-10 |
+------+------------+
2 rows in set (0.00 sec)
incorrect data format
mysql> INSERT INTO DATE12(datas) VALUES('10001-13-12');
Query OK, 1 row affected, 1 warning (0.03 sec)
mysql> SELECT * FROM DATE12;
+------+------------+
| id | datas |
+------+------------+
| NULL | 1987-11-04 |
| NULL | 0987-10-10 |
| NULL | 0000-00-00 |
But for time type all good
mysql> INSERT INTO time1(t) VALUE('-1112:45:12');
Query OK, 1 row affected, 1 warning (0.02 sec)
mysql> SELECT * FROM time1;
+------+------------+
| id | t |
+------+------------+
| NULL | NULL |
| NULL | -12:45:12 |
| NULL | -838:59:59 |
+------+------------+
3 rows in set (0.00 sec)
mysql> INSERT INTO time1(t) VALUE('11112:45:12');
Query OK, 1 row affected, 1 warning (0.02 sec)
mysql> SELECT * FROM time1;
+------+------------+
| id | t |
+------+------------+
| NULL | NULL |
| NULL | -12:45:12 |
| NULL | -838:59:59 |
| NULL | 838:59:59 |
+------+------------+
4 rows in set (0.00 sec)
mysql>
...Why insered '987-10-10' not '1000-01-01' ?
As per documentation on The DATE, DATETIME, and TIMESTAMP Types
For the DATE and DATETIME range descriptions, “supported” means that although earlier values might work, there is no guarantee.
Meaning, the dates prior to '1000-01-01' may also be accepted, but not guaranteed.
And hence, in your case the date entry '987-10-10' is accepted with no errors.
And you claim that '1000-01-01' is not inserted. But you actually tried '10001-13-12'.
And even if you try with '1000-13-12', it will fail, because, value '13' for 'month' part is meaning less.
As per documentation on Date and Time Literals
As a string with no delimiters in either 'YYYYMMDD' or 'YYMMDD' format, provided that the string makes sense as a date. For example, '20070523' and '070523' are interpreted as '2007-05-23', but '071332' is illegal (it has nonsensical month and day parts) and becomes '0000-00-00'.
Though not seen in the documentation, the above statement is also valid for format like 'YYYY-MM-DD' and others. And the same is shown in the following example:
mysql> insert into vdt(dt) values( '1001-13-32' );
ERROR 1292 (22007): Incorrect date value: '1001-13-32' for column 'dt' at row 1
mysql> select date_format( '2013-13-32', '%Y-%m-%d' ); show warnings;
+-----------------------------------------+
| date_format( '2013-13-32', '%Y-%m-%d' ) |
+-----------------------------------------+
| NULL |
+-----------------------------------------+
1 row in set, 1 warning (0.00 sec)
+---------+------+----------------------------------------+
| Level | Code | Message |
+---------+------+----------------------------------------+
| Warning | 1292 | Incorrect datetime value: '2013-13-32' |
+---------+------+----------------------------------------+
1 row in set (0.00 sec)
mysql> select str_to_date( '20131232', '%Y%m%d' ); show warnings;
+-------------------------------------+
| str_to_date( '20131232', '%Y%m%d' ) |
+-------------------------------------+
| NULL |
+-------------------------------------+
1 row in set, 1 warning (0.00 sec)
+---------+------+---------------------------------------------------------------+
| Level | Code | Message |
+---------+------+---------------------------------------------------------------+
| Warning | 1411 | Incorrect datetime value: '20131232' for function str_to_date |
+---------+------+---------------------------------------------------------------+
There is an article about SQL injection: Abusing MySQL string arithmetic for tiny SQL injections
The question is, what is the meaning of select ''-'' ? I try it with MySQL, and it returns:
mysql> select ''-'';
+-------+
| ''-'' |
+-------+
| 0 |
+-------+
1 row in set (0.00 sec)
What happend? What means that 0?
And the result of select '-':
mysql> select '-';
+---+
| - |
+---+
| - |
+---+
1 row in set (0.00 sec)
I am very confused about these result.
You are minus - from one empty string '' to other:
See following:
mysql> select '';
+--+
| |
+--+
| |
+--+
1 row in set (0.00 sec)
mysql> select '3'-'2';
+---------+
| '3'-'2' |
+---------+
| 1 |
+---------+
1 row in set (0.00 sec)
But warning if its not a number string:
mysql> select 'a'-'b';
+---------+
| 'a'-'b' |
+---------+
| 0 |
+---------+
1 row in set, 2 warnings (0.00 sec)
Two warnings:
mysql> SHOW WARNINGS LIMIT 2
-> ;
+---------+------+---------------------------------------+
| Level | Code | Message |
+---------+------+---------------------------------------+
| Warning | 1292 | Truncated incorrect DOUBLE value: 'a' |
| Warning | 1292 | Truncated incorrect DOUBLE value: 'b' |
+---------+------+---------------------------------------+
2 rows in set (0.00 sec)
Why no warning for empty string?
Where as there is no warning for empty string because its(casted something) 0 see below:
mysql> SELECT 0 = '';
+--------+
| 0 = '' |
+--------+
| 1 |
+--------+
1 row in set (0.00 sec)
hence by doing ''-'' you are doing 0 - 0
mysql> SELECT '' - '';
+---------+
| '' - '' |
+---------+
| 0 |
+---------+
1 row in set (0.00 sec)
To be more clear I am adding following example (I feels will be helpful to you):
How conversion happen:
mysql> SELECT '0' = 0
-> ;
+---------+
| '0' = 0 |
+---------+
| 1 |
+---------+
1 row in set (0.00 sec)
notice its conversion:
mysql> SELECT '' = '0'
-> ;
+----------+
| '' = '0' |
+----------+
| 0 |
+----------+
1 row in set (0.00 sec)
'' converted into 0, '0' converted into 0 but '' not equals to '0'
mysql> SELECT '1' = 1
-> ;
+---------+
| '1' = 1 |
+---------+
| 1 |
+---------+
1 row in set (0.00 sec)
mysql> SELECT '' = 1
-> ;
+--------+
| '' = 1 |
+--------+
| 0 |
+--------+
1 row in set (0.00 sec)
I'd explain select ''-'', which is the same as select '' - '', as select cast('' as int) - cast('' as int) which is select 0-0..
With select '-' you just get a string. Hope that makes sense...
'' is an empty string; - is subtraction. So you're subtracting one empty string from another. Subtraction is a numeric operator, so its result is a number, and mysql converts its arguments into numbers before subtracting them. The numeric value of '' is zero — but it doesn't matter very much, since any number subtracted from itself is going to give zero anyway.
mysql> select 28/4;
+--------+
| 28/4 |
+--------+
| 7.0000 |
+--------+
1 row in set (0.00 sec)
Is there a way I can set something system-wide to be more clever about this, or at least to automatically round every float to 2 places?
That's controlled by the div_precision_increment variable:
http://dev.mysql.com/doc/refman/5.1/en/server-system-variables.html#sysvar_div_precision_increment
MySQL> select ceiling(28/4);
+---------------+
| ceiling(28/4) |
+---------------+
| 7 |
+---------------+
1 row in set (0.00 sec)
MySQL> select format(28/4,0);
+----------------+
| format(28/4,0) |
+----------------+
| 7 |
+----------------+
1 row in set (0.00 sec)
I GOT IT !!!
set div_precision_increment = 0;
MySQL> select 28/4;
+------+
| 28/4 |
+------+
| 7 |
+------+
1 row in set (0.00 sec)
You could also set it globally:
set global div_precision_increment = 0;
or add this to /etc/my.cnf
div_precision_increment=0
I think your answer, if it exists, lies on this page
I have to be honest, I read through the rules about how precision is applied and don't really understand how you end up with 5 digits of precision by diving 28 by 4.
Good luck!