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16 Cards in this Set
- Front
- Back
Define Constraints?
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A contraint allows the database designer to enforce business rules about the data stored in the database's tables and the relationships between tables.
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What are the types of table constraints?
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1- Not Null (needs a value, it doesnot have to be unique)
2- Unique Key (every value in the column must be unique but null values are allowed). 3- Primary Key (unique values in the column but can't have null) 4- Foreign Key (Every value in the column must match with a value in another column in this table or another table, otherwise the value is null) 5- Check (The value must match one of the specified value in this column). |
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Where does the constraint informations are stored?
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They are stored in DD Views
1- DBA_CONSTRAINTS 2- DBA_CONS_COLUMNS. |
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Give SQL Example of adding a Primary Key?
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SQL>ALTER TABLE DEPT add constraint DEPT_PK primary key (DEPTNO);
SQL>CREATE TABLE EMP(empno number(4) constraint EMP_PK primary key, empname varchar2(10), deptno number(2) constraint EMP_PK_DEPTNO references DEPT(deptno)) |
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Define Segment?
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A segment is defined as any entity that consumes physical storage within the database.
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What are the types of segments?
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1- Table (stores data in rows and columns)
2- Index(Improves access to the table data) 3- Rollback (to maintain read consistency and perform transaction recovery) 4- Partition (Divides table into smaller, more manageable pieces for performance purposes) |
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Define Extent?
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Each Oracle segment is made up of continous chun of storage space in the database called extent.
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What is the minimum and maximum size of a segment in terms of extents?
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At least 1 extent per segment but a segment can have as many as 2 Billion extents.
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Define Blocks?
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Each extent is made up of smaller chunks of space called blocks.
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What is the minimum and maximum size of a extent in terms of blocks?
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The minimum size of an extent is 5 blocks.
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What is the size of blocks?
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The default size of a block is determined at the time of database creation.
The common database block sizes are 2KB, 4KB, 8KB and 16KB. |
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What is a block composed of?
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It is made up of Operating System blocks whose size is determined by the operating system, the most common size is 512 bytes.
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What are the types of SQL Statement?
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1-Queries created using SQL
2-DML (Insert, Update and Delete) 3-DDL (Create, Alter, Drop) 4-DCL (Grant and Revoke) |
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What are the benefits of PL/SQL on SQL?
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SQL doesnot support:
1- Condition Testing 2- Looping 3- Exception Handling. |
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What are the types of PL/SQL Objects?
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1- Anonymous Block (a block of PL/SQL code that is not stored in the database, but instead its embedded in a form, webpage, or SQL script)
2-Procedure (the code in the database which performs a specific action) 3- Function (the PL/SQL code that is stored in the database and return a value) 4- Package(collection of related functions and procedures) 5- Trigger(the code which runs whenever some activity occurs). |
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What are the categories of Oracle Server Architecture?
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1- User-related processes
2- Oracle Instance (memory structure) 3- Database (physical file structure). |