SQL进阶---第一单元(第七到第十课)、Manipulation


SQL进阶---第一单元、Manipulation

第七课、Update

MANIPULATION 
Update

UPDATE celebsSET age = 22

        WHERE id = 1;

The 

UPDATE

 statement
edits a row in thetable. You can use the 

UPDATE

statement
when you want tochange existing records.
1. 

UPDATE

 is
a clause that edits a rowin the table. 
2. 

celebs

 is
the name of the table. 

3. 

SET

 is
a clause that indicates the column to edit.

age

 is
the name of the column that is going to be updated

22

 is
the new value that is going to be inserted into the 

age

 column.

4. 

WHERE

 is
a clause that indicateswhich row(s) to update with the new column value.
Here the row with a 

1

in
the 

id

 column
is the row that will havethe 

age

 updated
to 

22

.
Instructions
1.Add
a new column to the table.In the code editor type

ALTER TABLE
celebs

       
ADD COLUMN twitter_handle TEXT;

SELECT
* FROM
celebs;
ALTER TABLE celebs

        
ADD COLUMNtwitter_handle TEXT;
SELECT * FROM celebs ;

Query Results

id

name

age

twitter_handle

1

Justin Bieber

22

 

2

Beyonce Knowles

33

 

3

Jeremy Lin

26

 

4

Taylor Swift

26

 

Database Schema

Celebs        
4 rows

Id

INTEGER

name

TEXT

age

INTEGER

twitter_handle

TEXT

第八课、Alter

MANIPULATION 
Alter

ALTER TABLE celebs

        ADD COLUMN twitter_handle TEXT;

The 

ALTER
TABLE

 statement added a new columnto
the table. You can use this command when you want to add columns to a table.
1. 

ALTER
TABLE

 is a clause that lets youmake
the specified changes. 
2. 

celebs

 is
the name of the table that isbeing changed. 

3. 

ADD COLUMN

 is
a clause that lets you add a new column to a table. 

twitter_handle

 is
the name of the new column being added

TEXT

 is
the data type for the new column

4.

NULL

 is a special value in SQLthat represents missing or unknown
data. Here, the rows that existed before thecolumn was added have 

NULL

 values
for 

twitter_handle

.

Instructions

1.Update the table to include Taylor Swift's
twitter handle. Inthe code editor type:

UPDATE celebs

        SET twitter_handle = '@taylorswift13'

        WHERE id = 4;

SELECT * FROM celebs;

UPDATE celebs

SET twitter_handle = '@taylorswift13'

WHERE id = 4;      
SELECT * FROM celebs;

QueryResults

id

name

age

twitter_handle

1

Justin Bieber

22

 

2

Beyonce Knowles

33

 

3

Jeremy Lin

26

 

4

Taylor Swift

26

@taylorswift13

DatabaseSchema

Celebs    
4 rows

Id

INTEGER

name

TEXT

age

INTEGER

twitter_handle

TEXT

2.Delete
all of the rows that have a NULL value
in the twittercolumn. Replace your code in the code editor with the following:

UPDATE
celebs

       
SETtwitter_handle
= '@taylorswift13'

       
WHERE
id = 4;

DELETE FROM
celebs

       
WHERE
twitter_handle ISNULL;

SELECT
* FROM
celebs;
UPDATE celebs

                 
SETtwitter_handle = '@taylorswift13'
                         
WHEREid = 4;
DELETE FROM celebs
        
WHEREtwitter_handle IS NULL;
SELECT * FROM celebs;

QueryResults

id

name

age

twitter_handle

4

Taylor Swift

26

@taylorswift13

DatabaseSchema

Celebs    
1 rows

Id

INTEGER

name

TEXT

age

INTEGER

twitter_handle

TEXT

 

Contacts
  4 rows

id

INTEGER

name

TEXT

birthday

DATE

第九课、Delete

MANIPULATION 
Delete

DELETE FROM celebs WHERE twitter_handle IS NULL;

The 

DELETE
FROM

 statement deletes one or morerows
from a table. You can use the statement when you want to delete existingrecords.

DELETE FROM

 is
a clause that lets youdelete rows from a table.

celebs

 is
the name of the table we want to delete rows from.

WHERE

 is
a clause that lets youselect which rows you want to delete. Here we wantto delete all of the rows where the twitter_handle column 

ISNULL

.

IS NULL

 is
a condition in SQL thatreturns true when the value is 

NULL

 and
false otherwise.

In this lesson we have learned SQL statements that create, edit,and delete data. In the upcoming lessons we will learn how to use SQL to retrieveinformation from a database.

第十课、小结

MANIPULATION 
Generalizations

Congratulations! You've learned six commands commonly used tomanage data stored in a relational database. What can we generalize so far?

SQL is a programming language
designed to manipulate and manage datastored in relational databases.

A relationaldatabase is adatabase that organizes information into one or more tables.

A table is a collection of data organized intorows and columns.

A statement is a string of characters that thedatabase recognizes as a valid command.

CREATE TABLE

 creates
a new table.

INSERT INTO

 adds
a new row to a table.

SELECT

 queries
data from a table.

UPDATE

 edits
a row in a table.

ALTER TABLE

 changes
an existing table.

DELETE FROM

 deletes
rows from a table.