sql - How can I get count of nulls per database on a MySQL server? -

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i count of nulls on columns , tables each database on mysql server. result table should like:

+---------------+------------+ | database_name | null_count | +---------------+------------+ | database1     |          0 | | database2     |       5643 | | database3     |         72 | +---------------+------------+

however, wasn't able beyond count of nulls single table:

select concat('select', group_concat(' count(*) - count(', column_name, ') '  separator ' + '), 'from ', max(table_schema), '.', max(table_name)) @sql information_schema.columns table_schema = 'accidents' , table_name = 'nesreca';  prepare stmt @sql; execute stmt; deallocate prepare stmt;

do have idea?

ps: able result matlab code. however, solution within mysql preferred.

i think on right track dynamic sql. because want entire database , not single table, structure of query like:

select table_schema, sum(cnt) (select "table_schema", count(*) cnt "table_name" "column_name" null union       . . .      ) t group table_schema;

you can construct as:

set group_concat_max_len=1500000; set @subsql = '(select "@table_schema" table_schema, count(*) cnt `@table_schema`.`@table_name` `@column_name` null)';  select @subsql := group_concat(replace(replace(replace(@subsql, '@table_schema', table_schema                                                       ), '@table_name', table_name                                               ), '@column_name', column_name                                       ) separator ' union '                               ) information_schema.columns;  set @sql = concat('select table_schema, sum(cnt) numnulls (',                   @subsql,                   ') t group table_schema');  prepare stmt @sql; execute stmt; deallocate prepare stmt;

i should note default length intermediate value group_concat() small query. have adjust it. system variable group_concat_max_len (see here).


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