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 celebs SET age = 22 

        WHERE id = 1;

The UPDATE statement edits a row in thetable. You can use the UPDATEstatement 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 1in 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 IS NULL;

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.

1. DELETE FROM is a clause that lets youdelete rows from a table.

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

3. 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 IS NULL.

4. 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.