Display all data of all tables

DECLARE @sqlText VARCHAR(MAX)
SET @sqlText = ''
SELECT @sqlText = @sqlText + ' SELECT * FROM ' + QUOTENAME(name) + CHAR(13) FROM sys.tables
EXEC(@sqlText)

For mysql:

1. Run SELECT information_schema.TABLES.TABLE_NAME FROM information_schema.TABLES where table_schema='db_name'

2. Create a loop which will run select query for each table gotten from the first query.