1. Oracle SQL query contains several languages?
(1) Data Definition Language (DDL): Used to create, modify and delete database objects.
(2) data manipulation statements (DML): for manipulating data, including INSERT, UPDATE, DELETE, SELECT and the like.
(3) Data Control Language (DCL): for performing the operations and revoke privileges granted privilege, including the GRANT (grant permissions), REVOKE (revoking privileges) two commands. DCL statement is automatically commit the transaction.
(4) Transaction Control Language (TCL): used to maintain the consistency of data, including the COMMIT (commit the transaction), ROLLBACK (roll back the transaction) and SAVEPOINT (save set point) 3 statement.
2. alert graphics operations and the use of
(1) Add a table has been created a new column
(2) modify the data specified in the table column type and length Type
(3) delete the columns specified in the table
3. The significance of the existence of a dummy table?
Dumb single separate table is a table, a query for specific data.
4. The sequence of the meaning of existence? MySQL how to achieve sequence function?
The sequence generator generates a digital sequence, which can be used to automatically generate primary key, and master key can coordinate the operation of the multi-row or multi-table. May generate a unique value, such as: select seq_no.next_val from dual seq_no wherein a sequence object is created
MySQL functions may be used to achieve the sequence "AUTO_INCREMENT = n" option when building a table to specify the initial value of the increment.
5. Paging SQL
