How to query all tables in a database

Question

I'm writing MySQL to get all unique IDs from all tables in a database.

The database has tables like record_20181201, record_20181202, ...

The tables are automatically generated based on date (all tables have the same schema, and one column name is visitorId).

The SQL query I made is like,

SELECT UNIQUE(visitorId) FROM databaseName.record_20181201;

I can only query one table at a time using this..

Is there a way to query all tables in the database and select all unique visitorIds there?

Answer 1

SELECT DISTINCT VisitorID FROM DBName.Table1
 UNION 
SELECT DISTINCT VisitorID FROM DBName.Table2 
 UNION 
SELECT DISTINCT VisitorID FROM DBName.Table3

Try this!!!!!!Hope this helps..

Answer 2

You could generate a query string with UNION's from the INFORMATION_SCHEMA.

Then run that query, or put it in a view.

A UNION will return a unique combined result of the unioned queries.
While a UNION ALL would just stick the results together.

SELECT GROUP_CONCAT(Qry ORDER BY TblSchema, TblName SEPARATOR ' UNION ')
FROM
(
  SELECT 
   TABLE_SCHEMA as TblSchema,
   TABLE_NAME as TblName,
   CONCAT('select visitorId from ',TABLE_SCHEMA,'.',TABLE_NAME,'\r\n') as Qry
  FROM INFORMATION_SCHEMA.COLUMNS
  WHERE TABLE_NAME LIKE 'record_201812%' 
    AND COLUMN_NAME = 'visitorId'
) Q;

Answer 3

Run below query you will get a single query that will give unique visitorId from all table.

SELECT 
    CONCAT('SELECT DISTINCT visitorId FROM (',
            REPLACE(query_string, ',', ' UNION '),
            ') union_table') AS final_query
FROM
    (SELECT 
        CONCAT(GROUP_CONCAT('SELECT visitorId FROM ', table_name)) AS query_string
    FROM
        information_schema.tables
    WHERE
        table_name LIKE 'record_%') table_a; 

you will get below query that will fetch unique visitorId from all tables.

SELECT DISTINCT
    visitorId
FROM
    (
    SELECT visitorId FROM record_20181201 
        UNION 
    SELECT visitorId FROM record_20181202 
        UNION 
    SELECT visitorId FROM record_20181203
    ) union_table