从多个表中获取所有列的最大值

Question

how do i get the maximum primary key of all tables in my DB (mysql)?

I have following query to retrieve all columns from all tables that are primary key and is INT datatype from my_db database

SELECT 
    table_name, column_name
FROM
    INFORMATION_SCHEMA.COLUMNS
WHERE
    table_schema = 'my_db'
        AND column_key = 'PRI'
        AND data_type LIKE '%int%'
ORDER BY TABLE_NAME , COLUMN_NAME

but now, I'm stucked at getting the maximum values from all these columns across all table. Is there a way to achieve this? My expected output would be single integer number which is the largest across all these columns.

Thank you!

Answer 1

Assuming that all the columns have a compatible type (which you are checking for), then you can construct the query using the metadata:

select group_concat(replace(replace('select max([column_name]) from [table_name]', '[column_name]', column_name), '[table_name]', table_name)
                    separator '\nunion all\n')
from INFORMATION_SCHEMA.COLUMNS
where table_schema = 'my_db' and
     column_key = 'PRI' and
     data_type LIKE '%int%'
order by TABLE_NAME, COLUMN_NAME;

I would just copy the query and run it. But you can automate the process more by assigning the resulting string a variable and using prepare / exec .