Today I encountered a retention problem which is rather weird:
Execute the SQL statement insert into test.COLUMNS select * from information_schema.COLUMNS; error: ERROR 1406 (22001): Data Too Long, field len 30, data len 48
The background of the problem is probably like this:
1. In TiDB4.0 distributed database system, go to information_schema.TABLES to copy a table structure, and then create an identical empty table to a temporary database csdn.
2. Execute insert into test.COLUMNS select * from information_schema.COLUMNS in the command line of tidb;
3. Try mysqldump to export data from the TABLES table of information_schema and import it into the TABLES table on the csdn library, but it still reports an error.
4. Checked the two libraries information_schema and csdn library, the table structure is the same.
Look at the error, it should be that the field is only 30 in length, but the entered data lacks 48 strings, then carefully check the table structure
CREATE TABLE `TABLES` (
`TABLE_CATALOG` varchar(512) DEFAULT NULL,
`TABLE_SCHEMA` varchar(64) DEFAULT NULL,
`TABLE_NAME` varchar(64) DEFAULT NULL,
`COLUMN_NAME` varchar(64) DEFAULT NULL,
`ORDINAL_POSITION` bigint(64) DEFAULT NULL,
`COLUMN_DEFAULT` text DEFAULT NULL,
`IS_NULLABLE` varchar(3) DEFAULT NULL,
`DATA_TYPE` varchar(64) DEFAULT NULL,
`CHARACTER_MAXIMUM_LENGTH` bigint(21) DEFAULT NULL,
`CHARACTER_OCTET_LENGTH` bigint(21) DEFAULT NULL,
`NUMERIC_PRECISION` bigint(21) DEFAULT NULL,
`NUMERIC_SCALE` bigint(21) DEFAULT NULL,
`DATETIME_PRECISION` bigint(21) DEFAULT NULL,
`CHARACTER_SET_NAME` varchar(32) DEFAULT NULL,
`COLLATION_NAME` varchar(32) DEFAULT NULL,
`COLUMN_TYPE` text DEFAULT NULL,
`COLUMN_KEY` varchar(3) DEFAULT NULL,
`EXTRA` varchar(30) DEFAULT NULL,
`PRIVILEGES` varchar(80) DEFAULT NULL,
`COLUMN_COMMENT` varchar(1024) DEFAULT NULL,
`GENERATION_EXPRESSION` text NOT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_bin;
Seeing that there is a field EXTRA is `EXTRA` varchar(30) DEFAULT NULL, then check the value of the data in this field to see if it exceeds.
mysql-17:31:41> select length(EXTRA) l,EXTRA from information_schema.TABLES order by l desc limit 50;
+----+--------------------------------------------------+
| l | EXTRA |
+----+--------------------------------------------------+
| 48 | DEFAULT_GENERATED on update CURRENT_TIMESTAMP(3) |
| 48 | DEFAULT_GENERATED on update CURRENT_TIMESTAMP(3) |
| 48 | DEFAULT_GENERATED on update CURRENT_TIMESTAMP(3) |
| 48 | DEFAULT_GENERATED on update CURRENT_TIMESTAMP(3) |
| 48 | DEFAULT_GENERATED on update CURRENT_TIMESTAMP(3) |
| 48 | DEFAULT_GENERATED on update CURRENT_TIMESTAMP(3) |
| 48 | DEFAULT_GENERATED on update CURRENT_TIMESTAMP(3) |
| 48 | DEFAULT_GENERATED on update CURRENT_TIMESTAMP(3) |
Check to get length (extra), the maximum length is indeed 48, is it because of the character set, because the character set is different in a database like mysql, and the space occupied is different.
First look at the character set of the library, it is the same:
+----------+------------------------------------------------------------------+
| Database | Create Database |
+----------+------------------------------------------------------------------+
| csdn | CREATE DATABASE `csdn` /*!40100 DEFAULT CHARACTER SET utf8mb4 */ |
+----------+------------------------------------------------------------------+
+--------------------+--------------------------------------------------------------------------------+
| Database | Create Database |
+--------------------+--------------------------------------------------------------------------------+
| INFORMATION_SCHEMA | CREATE DATABASE `INFORMATION_SCHEMA` /*!40100 DEFAULT CHARACTER SET utf8mb4 */ |
+--------------------+--------------------------------------------------------------------------------+
Let's look at the definition of the character set in the following table, whether it is the same or not, it is also the same:
use information_schema;
CREATE TABLE `TABLES` (
`TABLE_CATALOG` varchar(512) DEFAULT NULL,
`TABLE_SCHEMA` varchar(64) DEFAULT NULL,
`TABLE_NAME` varchar(64) DEFAULT NULL,
`COLUMN_NAME` varchar(64) DEFAULT NULL,
`ORDINAL_POSITION` bigint(64) DEFAULT NULL,
`COLUMN_DEFAULT` text DEFAULT NULL,
`IS_NULLABLE` varchar(3) DEFAULT NULL,
`DATA_TYPE` varchar(64) DEFAULT NULL,
`CHARACTER_MAXIMUM_LENGTH` bigint(21) DEFAULT NULL,
`CHARACTER_OCTET_LENGTH` bigint(21) DEFAULT NULL,
`NUMERIC_PRECISION` bigint(21) DEFAULT NULL,
`NUMERIC_SCALE` bigint(21) DEFAULT NULL,
`DATETIME_PRECISION` bigint(21) DEFAULT NULL,
`CHARACTER_SET_NAME` varchar(32) DEFAULT NULL,
`COLLATION_NAME` varchar(32) DEFAULT NULL,
`COLUMN_TYPE` text DEFAULT NULL,
`COLUMN_KEY` varchar(3) DEFAULT NULL,
`EXTRA` varchar(30) DEFAULT NULL,
`PRIVILEGES` varchar(80) DEFAULT NULL,
`COLUMN_COMMENT` varchar(1024) DEFAULT NULL,
`GENERATION_EXPRESSION` text NOT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_bin;
use csdn;
CREATE TABLE `TABLES` (
`TABLE_CATALOG` varchar(512) DEFAULT NULL,
`TABLE_SCHEMA` varchar(64) DEFAULT NULL,
`TABLE_NAME` varchar(64) DEFAULT NULL,
`COLUMN_NAME` varchar(64) DEFAULT NULL,
`ORDINAL_POSITION` bigint(64) DEFAULT NULL,
`COLUMN_DEFAULT` text DEFAULT NULL,
`IS_NULLABLE` varchar(3) DEFAULT NULL,
`DATA_TYPE` varchar(64) DEFAULT NULL,
`CHARACTER_MAXIMUM_LENGTH` bigint(21) DEFAULT NULL,
`CHARACTER_OCTET_LENGTH` bigint(21) DEFAULT NULL,
`NUMERIC_PRECISION` bigint(21) DEFAULT NULL,
`NUMERIC_SCALE` bigint(21) DEFAULT NULL,
`DATETIME_PRECISION` bigint(21) DEFAULT NULL,
`CHARACTER_SET_NAME` varchar(32) DEFAULT NULL,
`COLLATION_NAME` varchar(32) DEFAULT NULL,
`COLUMN_TYPE` text DEFAULT NULL,
`COLUMN_KEY` varchar(3) DEFAULT NULL,
`EXTRA` varchar(30) DEFAULT NULL,
`PRIVILEGES` varchar(80) DEFAULT NULL,
`COLUMN_COMMENT` varchar(1024) DEFAULT NULL,
`GENERATION_EXPRESSION` text NOT NULL,
KEY `idx_pri` (`TABLE_SCHEMA`,`TABLE_NAME`,`COLUMN_KEY`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_binOf course, the solution is very simple, which is to modify the character length in the TABLES table on the csdn library:
alter table csdn.TABLES modify `EXTRA` varchar(128) DEFAULT NULL;
But why in the TABLES table of the information_schema library, why can there be access to 48 characters in `EXTRA` varchar(30) DEFAULT NULL, this question is worthy of follow-up research.