Mysql 分析表内容

Question

I forgotten the name of the SQL command to analyse the content of a table. The command I'm looking for shows me for each colum the min/max/avg length of the content. If I remember correctly it starts with a normal select

SELECT * FROM table foo bar

All google searches shows me aggregate functions or "analyse table". But that's not what I'm looking for.

Answer 1

https://dev.mysql.com/doc/refman/5.7/en/procedure-analyse.html

SELECT * FROM mytable PROCEDURE ANALYSE()

Note this is deprecated in MySQL 5.7 and removed in MySQL 8.0.

Hopefully someday there will be some other implementation (perhaps a MySQL Shell plugin) for users of 8.0.

Answer 2

Another way of doing this is to get the histogram of the table. It's more work, though. For example:

create table customer (
  name varchar(20),
  salary int
);

Then insert 1000 random rows in the table:

insert into customer (name, salary)
with recursive
c (it, name, salary) as (
  select 1,  substring(md5(rand()) from 1 for 10), 50000
 union all
  select
    it + 1,
    substring(md5(rand()) from 1 for 10),
    floor(rand() * (120000 - 22000 + 1)) + 22000
  from c
  where it < 1000
)
select name, salary from c;

Now that you have a table with data you can compute a histogram (with a single bucket) and get the value ranges for each column:

analyze table customer 
update histogram on name, salary with 1 buckets;

select column_name,
  histogram->>'$."buckets"[0][0]' as min_value,
  histogram->>'$."buckets"[0][1]' as max_value
from information_schema.column_statistics
where table_name = 'customer'

Result:

COLUMN_NAME  min_value                        max_value                      
-----------  -------------------------------  -------------------------------
name         base64:type254:MDA2NzM2YmUwYQ==  base64:type254:ZmZjNjJlYWNmMg==
salary       22089                            119840