Find all those columns which have only null values, in a MySQL table

Question

The situation is as follows:

I have a substantial number of tables, with each a substantial number of columns. I need to deal with this old and to-be-deprecated data

Answer 1

I am not an expert in SQL procedures, hence giving general idea using SQL queries and a PHP/python script.

• use SHOW TABLES or some other query on INFORMATION_SCHEMA database to get all tables in your database MY_DATABASE

• do a query to generate a statement to get all column names in a particular table, this will be used in next query.

 SELECT Group_concat(Concat( "MAX(", column_name, ")" ))
         FROM   information_schema.columns
         WHERE  table_schema = 'MY_DATABSE'
                AND table_name = 'MY_TABLE'
         ORDER  BY table_name,ordinal_position

• You will get an output like MAX(column_a),MAX(column_b),MAX(column_c),MAX(column_d)

• Use this output to generate final query :

SELECT Max(column_a), Max(column_b), Max(column_c), Max(column_d) FROM MY_DATABASE.MY_TABLE

The output would be :

   MAX(column_a)    MAX(column_b)   MAX(column_c)   MAX(column_d)
     NULL            1           NULL                1

• All the columns with Max value as NULL are the ones which have all values NULL