Sql Beginners

Front 1

candidate key

Back 1

for every table there is at least one column with the property than no two rows have the same combination of data values for these columns

Front 2

What if a table has more than 1 candidate key

Back 2

If there is more than one candidate key within a table the database designer designates one of them as the primary key of the table

Front 3

The DDL contains three generic SQL statements

Back 3

CREATE object
ALTER object
DROP object
This statements create, alter, and remove database objects (databases, tables, columns, indexes)

Front 4

DML encompasses

Back 4

all operations that manipulate the data.
SELECT - retrieval
INSERT - insertion
DELETE - deletion
UPDATE - updating

Front 5

normalizaton (def)

Back 5

process during which the existing tables of a database are tested to find certain dependencies between the columns of a table.If one of these generated tables till contains data dependencies, the process of normalization must be repeated until all dependencies are resolved.

Front 6

functional dependencie )def_

Back 6

means that by using the known value of one column, the corresponding value of another column can always be uniquely determined

Front 7

Syntaxis to create table and set primary key (used for when we have a single column as primary key)

Back 7

SQL Server

CREATE TABLE Persons
(
P_Id int NOT NULL PRIMARY KEY,
LastName varchar(255) NOT NULL,
FirstName varchar(255),
Address varchar(255),
City varchar(255)
)

Front 8

Create a primary key on multiple columns when creating a table

Back 8

CREATE TABLE Persons
(
P_Id int NOT NULL,
LastName varchar(255) NOT NULL,
FirstName varchar(255),
Address varchar(255),
City varchar(255),
CONSTRAINT pk_PersonID PRIMARY KEY (P_Id,LastName)
)

Front 9

Normalization of data

Back 9

Normalization of data is a process during which the existing tables of a database
are tested to find certain dependencies between the columns of a table. If such
dependencies exist, the table is restructured into multiple (usually two) tables, which
eliminates any column dependencies. If one of these generated tables still contains data
dependencies, the process of normalization must be repeated until all dependencies are
resolved.

Front 10

First Normal Form

Back 10

First normal form (1NF) means that a table has no multivalued attributes or composite
attributes. (A composite attribute contains other attributes and can therefore be divided
into smaller parts.) All relational tables are by definition in 1NF, because the value of
any column in a row must be atomic—that is, single valued

Front 11

Second Normal Form

Back 11

A table is in second normal form (2NF) if it is in 1NF and there is no nonkey column
dependent on a partial primary key of that table. This means if (A,B) is a combination
of two table columns building the key, then there is no column of the table depending
either on only A or only B.

Front 12

Third Normal Form

Back 12

A table is in third normal form (3NF) if it is in 2NF and there are no functional
dependencies between nonkey columns