Query related information such as tables and fields in the database (oracle, mysql, Dameng)

1. oracle database:

Query all users

select * from all_users 
-- where USERNAME like 'sys_%' 

Query all table information and query according to user

SELECT * FROM all_tables 
--WHERE OWNER = '' ORDER BY TABLE_NAME;

Count the number of tables and the amount of data recorded in the tables for a certain user

SELECT count(table_name),sum(num_rows) FROM all_tables WHERE OWNER = ''

Statistics table data size (M)

select c.segment_name,b.TABLE_NAME, c.bytes,round(c.bytes / 1024 / 1024, 2 )|| 'M' from 
(SELECT table_name FROM all_tables 
WHERE OWNER = '' ORDER BY TABLE_NAME
 ) b
LEFT JOIN user_segments c on c.segment_name = b.TABLE_NAME and segment_type = 'TABLE'

2.mysql database:

Query all table information

select * 
from 
information_schema.tables 
where 
table_schema='当前数据库'
#table_rows是记录数

Or if you just want to see the table name, you can use

show tables

Query information with empty field annotations

select
column_name,
column_comment,
table_name 
from information_schema.columns
where table_schema = '当前数据库'
and (column_comment  is null or column_comment ='') 

View field annotation information of a single table

show full columns from 表名;

Query table data length size

SELECT
table_comment,
table_name,
    concat( round(DATA_LENGTH / 1024 / 1024, 2 ), 'M' ) 
FROM
    information_schema.TABLES 
WHERE
    table_schema = '当前数据库' 
    

3. Dameng database:

Query table information under a certain mode

select * from sys.dba_tables where owner = '模式名'

--或者
select * from all_tables where owner = '模式名'

Dameng handles CLOB types:

dbms_lob.substr(clobcolumn,4000), intercept the CLOB field;

Dameng handles TEXT type:

convert(varchar(5000),TEXT field), process the TEXT type

Remove the non-numeric decimal point part in heji:

SELECT
  heji,
   REGEXP_REPLACE(heji, '[^0-9\.]+', '') AS stripped_column
FROM
  "test"."test";

4、prostgreSQL

Query table data volume, estimated value, inaccurate, accurate data is only one table statistics

(The statistics collector keeps track of roughly how many rows are "eventful" at any time (not deleted or discarded by later updates). Under heavy events, this value may be slightly off, but is usually a good estimate. , can also show how many rows have expired)

SELECT schemaname,relname,n_live_tup 
  FROM pg_stat_user_tables 
ORDER BY n_live_tup DESC;