MySQL Conclusion

1、Select total count from a table:

select  count(1)  from  'tablename'  where 1=1 ;

2、No where condition delete whole table data method:

SET SQL_SAFE_UPDATES=0 ;

3、How to connect String?

in MySQL: use concat(string1,string2);

4、How to Unique constraint on multiple fields?

alter table Variable_Entries add unique (var_id, value);

5、How to import sql-script to EER-diagram in mysql workbench?

in EER-Diagram perspective, select  FILE-->import-->Reverse Engineer MySQL Create Script,  OK!