1 record(s) selected.

db2 =>  select concat( abc , coalesce(col1,  )) as nullstring from t2

NULLSTRING

abc

  1 record(s) selected.

7.1.9  Record deletion

As some other competitive relational database management systems, MySQL 

introduced in Version V4.0 the TRUNCATE statement. TRUNCATE is used to 

delete all rows from a table when there is no need to recover the deleted records. 

Therefore, there is no ROLLBACK after a TRUNCATE is possible. Example 7 15 

shows how TRUNCATE is used to remove all rows, and does not allow a rollback 

of the deleted rows.

Example 7 15   Using MySQL TRUNCATE to delete all records in a file

mysql> select * from t1;

+      +

| col1 |

+      +

|    5 |

|   10 |

+      +

2 rows in set (0.02 sec)

mysql> truncate table t1;

Query OK, 0 rows affected (0.00 sec)

mysql> select * from t1;

Empty set (0.00 sec)

mysql> rollback

     > ;

ERROR 1196: Warning:  Some non transactional changed tables couldn t be rolled 

back

mysql> select * from t1;

Empty set (0.00 sec)

The TRUNCATE option is primarily used to quickly delete all records from a table 

when no recovery of the deleted rows is required. To achieve a similar behavior 

 Chapter 7. Application porting 

167