MYSQL - set default as NULL to all columns, where default is not set

问题

I have about 12 databases, each with 50 tables and most of them with 30+ columns; the db was running in strict mode as OFF, but now we had to migrate the db to cleardb service which by default has strict mode as ON. all the tables that had "Not Null" constraint, the inserts have stopped working, just because the default values are not being passed; while in case of strict mode as OFF if the value are not provided, the MYSQL will presume the default value of the column datatype. Is there a script I can use to get the metadata about all the columns of all tables and generate a script to alter all the tables with such columns to change the default to "Null"

回答1:

You should consider using the information_schema tables to generate DDL statements to alter the tables. This kind of query will get you the list of offending columns.

SELECT CONCAT_WS('.',TABLE_SCHEMA, TABLE_NAME, COLUMN_NAME) col  
  FROM information_schema.COLUMNS
 WHERE IS_NULLABLE = 0
   AND LENGTH(COLUMN_DEFAULT) = 0 
   AND TABLE_SCHEMA IN ('db1', 'db2', 'db3')

You can do similar things to generate ALTER statements to change the tables. But beware, MySQL likes to rewrite tables when you alter certain things. It might take time.

DO NOT attempt to UPDATE the information_schema directly!

You could try changing the strict_mode setting when you connect to the SaaS service, so your software will work compatibly.

This is a large project and is probably important business for cleardb. Why not ask them for help in changing the strict_mode setting?

回答2:

This is what I came up with on the base of @Ollie-jones script

https://gist.github.com/brijrajsingh/efd3c273440dfebcb99a62119af2ecd5

SELECT CONCAT_WS('.',TABLE_SCHEMA, TABLE_NAME, COLUMN_NAME) col,CONCAT('alter table ',TABLE_NAME,' MODIFY COLUMN ', COLUMN_NAME,' ',DATA_TYPE,'(',CHARACTER_MAXIMUM_LENGTH,') NULL DEFAULT NULL') as script_col
  FROM information_schema.COLUMNS
 WHERE is_nullable=0 
 and length(COLUMN_DEFAULT) is NULL and
 CHARACTER_MAXIMUM_LENGTH is not NULL and 
 table_schema = 'immh' 
 Union
 SELECT CONCAT_WS('.',TABLE_SCHEMA, TABLE_NAME, COLUMN_NAME) col,CONCAT('alter table ',TABLE_NAME,' MODIFY COLUMN ', COLUMN_NAME,' ',DATA_TYPE,' NULL DEFAULT NULL') as script_col
  FROM information_schema.COLUMNS
 WHERE is_nullable=0 
 and length(COLUMN_DEFAULT) is NULL and
 CHARACTER_MAXIMUM_LENGTH is NULL and 
 table_schema = 'immh'

来源：https://stackoverflow.com/questions/39079165/mysql-set-default-as-null-to-all-columns-where-default-is-not-set

标签

mysql

cleardb