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مثال از چند دستور sql server تاریخ درج: ١٣٩۶/٠۴/٢۶

 در این مقال به بررسی دستورات زیر می پردازیم:

creating a table

creating a view

inserting rows

updating rows

deleting rows

commit -- ـائید انجام تغییرات

rollback -- برگشت تغییرات

 
بررسی مثالهای تعاملی در SQL

create a table to store information about weather observation stations: 
-- No duplicate ID fields allowed

CREATE TABLE STATION 
(ID INTEGER PRIMARY KEY, 
CITY CHAR(20), 
STATE CHAR(2), 
LAT_N REAL, 
LONG_W REAL);

populate the table STATION with a few rows:

INSERT INTO STATION VALUES (13, 'Phoenix', 'AZ', 33, 112); 
INSERT INTO STATION VALUES (44, 'Denver', 'CO', 40, 105); 
INSERT INTO STATION VALUES (66, 'Caribou', 'ME', 47, 68);

query to look at table STATION in undefined order:

SELECT * FROM STATION;

ID CITY STATE LAT_N LONG_W
13 Phoenix AZ 33 112
44 Denver  CO 40 105
66 Caribou ME 47 68

query to select Northern stations (Northern latitude > 39.7): 
-- selecting only certain rows is called a "restriction".

SELECT * FROM STATION 
WHERE LAT_N > 39.7;

ID CITY STATE LAT_N LONG_W
44 Denver  CO 40 105
66 Caribou ME 47 68

query to select only ID, CITY, and STATE columns: 
-- selecting only certain columns is called a "projection".

SELECT ID, CITY, STATE FROM STATION;

ID CITY STATE
13 Phoenix AZ
44 Denver  CO
66 Caribou ME

query to both "restrict" and "project":

SELECT ID, CITY, STATE FROM STATION 
WHERE LAT_N > 39.7;

ID CITY STATE
44 Denver  CO
66 Caribou ME

create another table to store normalized temperature and precipitation data: 
-- ID field must match some STATION table ID 
(so name and location will be known). 
-- allowable ranges will be enforced for other values. 
-- no duplicate ID and MONTH combinations. 
-- temperature is in degrees Fahrenheit. 
-- rainfall is in inches.

CREATE TABLE STATS 
(ID INTEGER REFERENCES STATION(ID), 
MONTH INTEGER CHECK (MONTH BETWEEN 1 AND 12), 
TEMP_F REAL CHECK (TEMP_F BETWEEN -80 AND 150), 
RAIN_I REAL CHECK (RAIN_I BETWEEN 0 AND 100), 
PRIMARY KEY (ID, MONTH));

populate the table STATS with some statistics for January and July:

INSERT INTO STATS VALUES (13, 1, 57.4, 0.31); 
INSERT INTO STATS VALUES (13, 7, 91.7, 5.15); 
INSERT INTO STATS VALUES (44, 1, 27.3, 0.18); 
INSERT INTO STATS VALUES (44, 7, 74.8, 2.11); 
INSERT INTO STATS VALUES (66, 1, 6.7, 2.10); 
INSERT INTO STATS VALUES (66, 7, 65.8, 4.52);

query to look at table STATS in undefined order:

SELECT * FROM STATS;

ID MONTH TEMP_F RAIN_I
13 1 57.4 .31
13 7 91.7 5.15
44 1 27.3 .18
44 7 74.8 2.11
66 1 6.7 2.1
66 7 65.8 4.52
 

query to look at table STATS, picking up location information by joining with table STATION on the ID column: 
-- matching two tables on a common column is called a "join". 
-- the column names often match, but this is not required. 
-- only the column values are required to match.

SELECT * FROM STATION, STATS 
WHERE STATION.ID = STATS.ID;

ID CITY ST LAT_N  LONG_W ID MONTH  TEMP_F RAIN_I
13 Phoenix  AZ 33  112 13 57.4 .31 
13 Phoenix  AZ 33  112 13 91.7 5.15 
44 Denver CO 40  105 44 27.3 .18 
44 Denver CO 40  105 44 74.8 2.11 
66 Caribou  ME 47  68 66 6.7 2.1 
66 Caribou  ME 47  68 66 65.8 4.52 

 

query to look at the table STATS, ordered by month and greatest rainfall, with columns rearranged:

SELECT MONTH, ID, RAIN_I, TEMP_F 
FROM STATS 
ORDER BY MONTH, RAIN_I DESC;

MONTH ID RAIN_I TEMP_F
1 66 2.1 6.7
1 13 .31 57.4
1 44 .18 27.3
7 13 5.15 91.7
7 66 4.52 65.8
7 44 2.11 74.8
 

 

query to look at temperatures for July from table STATS, lowest temperatures first, picking up city name and latitude by joining with table STATION on the ID column:

SELECT LAT_N, CITY, TEMP_F 
FROM STATS, STATION 
WHERE MONTH = 7 
AND STATS.ID = STATION.ID 
ORDER BY TEMP_F;

LAT_N CITY  TEMP_F
47 Caribou  65.8
40 Denver  74.8
33 Phoenix  91.7
 

 

query to show MAX and MIN temperatures as well as average rainfall for each station:

SELECT MAX(TEMP_F), MIN(TEMP_F), AVG(RAIN_I), ID 
FROM STATS 
GROUP BY ID;

MAX(TEMP_F) MIN(TEMP_F) AVG(RAIN_I) ID
91.7 57.4  2.73  13
74.8 27.3  1.145  44
65.8 6.7  3.31  66
 

 

query (with subquery) to show stations with year-round average temperature above 50 degrees: 
-- rows are selected from the STATION table based on related values in the STATS table.

SELECT * FROM STATION 
WHERE 50 < (SELECT AVG(TEMP_F) FROM STATS 
WHERE STATION.ID = STATS.ID);

ID CITY  ST LAT_N LONG_W
13 Phoenix  AZ 33 112
44 Denver  CO 40 105
 

 

create a view (derived table or persistent query) to convert Fahrenheit to Celsius and inches to centimeters:

CREATE VIEW METRIC_STATS (ID, MONTH, TEMP_C, RAIN_C) AS 
SELECT ID, 
MONTH, 
(TEMP_F - 32) * 5 /9, 
RAIN_I * 0.3937 
FROM STATS;

query to look at table STATS in a metric light (through the new view):

SELECT * FROM METRIC_STATS;

ID MONTH TEMP_C RAIN_C
13 1 14.1111111 .122047
13 7 33.1666667 2.027555
44 1 -2.6111111 .070866
44 7 23.7777778 .830707
66 1 -14.055556 .82677
66 7 18.7777778 1.779524
 

 

another metric query restricted to January below-freezing (0 Celsius) data, sorted on rainfall:

SELECT * FROM METRIC_STATS 
WHERE TEMP_C < 0 AND MONTH = 1 
ORDER BY RAIN_C;

ID MONTH TEMP_C RAIN_C
44 1 -2.6111111 .070866
66 1 -14.055556 .82677
 

 

 


 

 

Interactive SQL Update Examples

update all rows of table STATS to compensate for faulty rain gauges known to read 0.01 inches low:

UPDATE STATS SET RAIN_I = RAIN_I + 0.01;

and take a look:

SELECT * FROM STATS;

ID MONTH TEMP_F RAIN_I
13 1 57.4 .32
13 7 91.7 5.16
44 1 27.3 .19
44 7 74.8 2.12
66 1 6.7 2.11
66 7 65.8 4.53
 

 

update one row, Denver's July temperature reading, to correct a data entry error:

UPDATE STATS SET TEMP_F = 74.9 
WHERE ID = 44 
AND MONTH = 7;

and take a look:

SELECT * FROM STATS;

ID MONTH TEMP_F RAIN_I
13 1 57.4 .32
13 7 91.7 5.16
44 1 27.3 .19
44 7 74.9 2.12
66 1 6.7 2.11
66 7 65.8 4.53
 

 

make the above changes permanent: 
-- they were only temporary until now.

COMMIT WORK;

update two rows, Denver's rainfall readings:

UPDATE STATS SET RAIN_I = 4.50 
WHERE ID = 44;

and take a look:

SELECT * FROM STATS;

ID MONTH TEMP_F RAIN_I
13 1 57.4 .32
13 7 91.7 5.16
44 1 27.3 4.5
44 7 74.9 4.5
66 1 6.7 2.11
66 7 65.8 4.53
 

 

Oops! We meant to update just the July reading! Undo that update: 
-- undoes only updates since the last COMMIT WORK.

ROLLBACK WORK;

and take a look:

SELECT * FROM STATS;

ID MONTH TEMP_F RAIN_I
13 1 57.4 .32
13 7 91.7 5.16
44 1 27.3 .19
44 7 74.9 2.12
66 1 6.7 2.11
66 7 65.8 4.53
 

 

now update Denver's July rainfall reading and make it permanent:

UPDATE STATS SET RAIN_I = 4.50 
WHERE ID = 44 
AND MONTH = 7;

COMMIT WORK;

and take a look:

SELECT * FROM STATS;

ID MONTH TEMP_F RAIN_I
13 1 57.4 .32
13 7 91.7 5.16
44 1 27.3 .19
44 7 74.9 4.5
66 1 6.7 2.11
66 7 65.8 4.53
 

 

delete July data and East Coast data from both tables: 
-- note that we use longitude values from the related STATION table to determine which STAT stations were east of 90 degrees.

DELETE FROM STATS 
WHERE MONTH = 7 
OR ID IN (SELECT ID FROM STATION 
WHERE LONG_W < 90);

DELETE FROM STATION WHERE LONG_W < 90;

COMMIT WORK;

and take a look:

SELECT * FROM STATION;

ID CITY  ST LAT_N LONG_W
13 Phoenix  AZ 33 112
44 Denver  CO 40 105
 

SELECT * FROM STATS;

ID MONTH TEMP_F RAIN_I
13 1 57.4 .32
44 1 27.3 .19
 

 

View METRIC_STATS, a Fahrenheit-to-Centigrade and inches-to-centimeters conversion of table STATS, reflects the updates made to the underlying table.

SELECT * FROM METRIC_STATS;

ID MONTH TEMP_C RAIN_C
13 1 14.1111111 .125984
44 1 -2.6111111 .074803
 

 

 

SQL Constraints

SQL enforces data integrity constraints.

Attempt to insert a row for an unknown observation station. 
-- The ID value of 33 does not match a station ID value in the STATION table. 
-- This is a violation of referential integrity.

INSERT INTO STATS VALUES (33,8,27.4,.19);

error message
violation of constraint STATS_FOREIGN1 caused operation to fail 

 

Attempt to update a row with a temperature below the range -80 TO 150.

UPDATE STATS SET TEMP_F = -100 WHERE ID = 44 AND MONTH = 1;

error message
violation of constraint STATS_CHECK2 caused operation to fail 

 

Attempt to insert a row with negative rainfall measurement, outside the range 0 to 100.

INSERT INTO STATS VALUES (44,8,27.4,-.03);

error message
violation of constraint STATS_CHECK3 caused operation to fail 

 

Attempt to insert a row with month 13, outside the range of 1 to 12.

INSERT INTO STATS VALUES (44,13,27.4,.19);

error message
violation of constraint STATS_CHECK1 caused operation to fail 

 

Attempt to insert a row with a temperature above the range -80 TO 150.

INSERT INTO STATS VALUES (44,8,160,.19);

error message
violation of constraint STATS_CHECK2 caused operation to fail 

 

Attempt to insert a row with no constraint violations.

INSERT INTO STATS VALUES (44,8,27.4,.10);

status message
1 row inserted 

 

and take a look:

SELECT * FROM STATS;

ID MONTH TEMP_F RAIN_I
44 8 27.4 .10
13 1 57.4 .32
44 1 27.3 .19

 

Attempt to insert a second row of August statistics for station 44. 
-- This is a violation of the primary key constraint. 
-- Only one row for each station and month combination is allowed.

INSERT INTO STATS VALUES (44,8,160,.19);

error message
violation of constraint STATS_PRIMARY_ID_MONTH caused operation to fail 

تگها: sql   آموزش sql   آموزش دستورات sql server   
 

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