Shulou(Shulou.com)06/01 Report--

1. What is the primary key?

Answer: a combination of data columns and rows that can be uniquely and fully identified in a data table can only have one and cannot be empty.

2. What are foreign keys?

Answer: there is a foreign key for another table in one table.

3. The difference between stored procedures and triggers

A: triggers are very similar to stored procedures. Triggers are also sets of sql statements. The only difference between them is that triggers cannot use execute statements. Instead, they automatically trigger execution when the user executes a Transact-SQL statement.

A trigger is a stored procedure that modifies the execution of the data in the specified table. It is common to create triggers to enforce referential integrity and consistency of logically related data in different tables. Because users cannot bypass triggers, they can be used to enforce complex business rules to ensure data integrity.

Triggers are different from stored procedures, triggers are mainly triggered by event execution, and stored procedures can be called directly through the name of the stored procedure.

4. What are the advantages of using stored procedures to access the database than using SQL statements directly?

Answer: (1) the stored procedure is precompiled and does not need to be compiled again, so it is more efficient to execute

(2) A batch of SQL statements are encapsulated in the stored procedure to facilitate the maintenance of data integrity.

(3) Code reuse can be realized.

5. What is the difference between function and procedure in Oracle?

1)。 It can be understood that function is a kind of stored procedure.

2)。 A function can have no parameters, but must need a return value, and a stored procedure can have no parameters and no need to return a value

3)。 The return value of the function return does not return the parameter mode. The stored procedure returns the value through the out parameter. If you need to return multiple parameters, it is recommended to use the stored procedure.

4)。 In sql data manipulation statements, only functions can be called, not stored procedures.

6. What kinds of files are there in Oracle?

Answer: data file (usually suffixed with .dbf or .ora), log file (suffix .log), control file (suffix .ctl)

7. Simple data manipulation

Select 、 insert 、 update 、 delete 、 create 、 drop 、 truncate

Create a table

Create table table_name (column name, data type [not null])

Query the table

Select * [column name] expression from table name where conditional order by alias

3. Delete

Delete from table name where condition

4. Update

Update table name set column name 1 = value, column name 2 = value.... where condition

5. Add

Insert into table name (column name 1, column name 2...) values (value 1, value 2...)

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