SQL進階---第一單元(第七到第十課)、Manipulation
SQL進階---第一單元、Manipulation
第七課、Update
MANIPULATIONUpdate
UPDATE celebs SET 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 theage
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
ALTERTABLE 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
Celebs4rows
Id
INTEGER
name
TEXT
age
INTEGER
twitter_handle
TEXT
第八課、Alter
MANIPULATIONAlter
ALTERTABLE 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 column4.
NULL
is a special value in SQLthat represents missing or unknown data. Here, the rows that existed before thecolumn was added haveNULL
values fortwitter_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
Celebs4 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;
DELETEFROM 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
Celebs1 rows
Id
INTEGER
name
TEXT
age
INTEGER
twitter_handle
TEXT
Contacts 4 rows
id
INTEGER
name
TEXT
birthday
DATE
第九課、Delete
MANIPULATIONDelete
DELETEFROM celebs WHERE twitter_handle ISNULL;
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 columnIS NULL
. -
IS NULL
is a condition in SQL thatreturns true when the value isNULL
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.
第十課、小結
MANIPULATIONGeneralizations
Congratulations! You've learned six commands commonly used tomanage data stored in a relational database. What can we generalize so far?
-
SQLis 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.
-