问题
Is it possible to select entire row in a table and get sort of checksum? I am looking for a way to tell my code to update data only if at least one record has been changed. From perspective of data changes tracking it would help me to size down a number of changes noted in history table. - Thanks.
回答1:
You can combine the MD5() and CONCAT() functions to generate an MD5 checksum for the row:
SELECT MD5(CONCAT(col1, col2, col3, ...)) as MD5_checksum FROM table;
If one of the columns is nullable, be sure you wrap it in IFNULL(col, ''), as a null will make the result of the CONCAT() also null.
Also be aware that this is not 100% safe. If you remove the 1 character from a column and add it as the first character of the next column, the outcome of the CONCAT() and thus of the MD5 hash will be the same.
回答2:
You can check changes by comparing your old checksum value with current checksum.
CHECKSUM TABLE tbl_name
回答3:
yes you can use the mentioned code
SELECT ROW_COUNT();
and then use the condition of like if Row_Count()>1 then you can process the data Hope it works
回答4:
Extending Ivars answer for a more robust MD5 checksum of columns;
If concating a NULL field you will not get any result. If its NULL replace the field with the letter 'A'.
SELEECT MD5(concat(IFNULL(col1, "A"), IFNULL(col2, "A"), IFNULL(col3, "A")))
AS md5_checksum FROM tbl_name;
回答5:
This one worked very well to me, in order to make sure database structure at all tables are the same as before:
SET SESSION group_concat_max_len = 1000000;
SELECT MD5( GROUP_CONCAT( CONCAT( TABLE_NAME, COLUMN_NAME, DATA_TYPE, COLUMN_TYPE ) ) ) AS md5 FROM INFORMATION_SCHEMA.COLUMNS WHERE TABLE_SCHEMA = '{your_database_name}';
来源：https://stackoverflow.com/questions/35196807/mysql-rows-checksum