Computational Thinking Exercises - SET 2 Insert, Update & Delete

Transcription

1 Insert, Update & Delete Name: Mark: / 37 Modifying Database Data It is important that any store of information is accurate and up-to-date. Structured Query Language includes syntax that allows programmers to insert new rows (records), update existing information and delete information from one or more tables in a database. Starting with this table, called Hardware, the examples below show how the table can be modified using SQL instructions. Hardware Example 1 INSERT INTO Hardware (StockCode, Manufacturer, Category, Price) VALUES ( MOU667, Microsoft, Mouse,35.00); The INSERT INTO VALUES instruction is used to select the name of the table and the columns (fields) into which new data will be added. If a complete new row is being added there is no need to list the columns. INSERT INTO Hardware would work just as well in the example. Example 2 UPDATE Hardware SET Price = 33.5 WHERE StockCode = MOU667 ; The UPDATE instruction is used to SET or change data in a database (for example SET Price = 33.5). The correct row or rows are identified using the WHERE command. Note: Without the WHERE identifying one or more rows, every value in the price column would be SET to Example 3 DELETE FROM Hardware WHERE Manufacturer = Dell AND Category = Keyboard ; The DELETE FROM instruction is used to remove a row from a database table. The WHERE part of the instruction is used to identify the one or more rows that will be deleted. Although the example only shows one row being deleted from the database, in a larger table (with more data) every Keyboard manufactured by Dell would be removed from the database. Copyright Mr Greg Reid, April

2 Problems 1 - What s Changed? Starting with a table called Bikes you must calculate what SQL instruction has been used to make the changes shown from the original table. Bikes For example WHERE Maker = Boardman ; Modified Bikes Throughout these exercises you will be awarded 1 mark for every correct line in each SQL instruction. Each of your answers in the first set of problems should include one INSERT or UPDATE or DELETE instruction and may involve two or three lines of SQL. Your thinking should be ordered as follows: work out which type of instruction has been used first (INSERT, UPDATE or DELETE) then work out what specifically has changed in the table finally work out how the rows where the changes occurred were identified. a) What SQL instruction has modified the original Bikes WHERE Maker = Raleigh ; b) What SQL instruction has modified the original Bikes WHERE Type = Mountain ; c) What SQL instruction has modified the original Bikes SET Gears = 24 WHERE Model = MB Comp ; 2

3 Bikes d) What SQL instruction has modified the original Bikes SET Type = MBX WHERE Type = Mountain ; e) What SQL instruction has modified the original Bikes INSERT INTO Bikes VALUES ( Raleigh, Hybrid, Edale,21); f) What SQL instruction has modified the original Bikes SET Gears = 1 WHERE Maker = Boardman ; g) What SQL instruction has modified the original Bikes WHERE Gears < 20; 3

4 Problems 2 - Show Your Working These questions will again use the Bikes table. The next set of questions will include two or more SQL instructions. You will be expected to note the effect of executing these instructions on a copy of the Bikes table. For the questions below mark the following on each copy of the bikes table: for a DELETE instruction score out the identified row/rows for an UPDATE instruction score out the previous value and write in the new one for an INSERT instruction write the new values in the space provided For example: WHERE Maker = Boardman AND Type = Road ; SET Type = Hybrid, Model = Duo WHERE Maker = Carerra AND Type = Mountain ; INSERT INTO Bikes VALUES ( Raleigh, Hybrid, Edale,21); Note that a few of these questions include changes that would never actually be made to a Bikes database (for example, changing the Maker of a bike because it has a certain number of Gears). Please ignore this as the questions are designed simply to test your problem solving skills. a) WHERE Type = Road ; SET Maker = Apollo, Gears = 16 WHERE Model = Kraken ; the above table. (2) b) SET Maker = Falcon, Type = Hybrid WHERE Model = Cuckoo ; WHERE Type = Hybrid ; the above table. (2) 4

5 c) INSERT INTO Bikes VALUES ( Viking, Road, Axe,27) SET Type = Road, WHERE Type= Hybrid AND Gears>20; WHERE Type = Road OR Gears > 10; the above table. (3) d) SET Maker = Carerra WHERE Model = Raleigh ; SET Type = Hybrid WHERE Gears > 20; WHERE Maker = Carerra AND Type = Hybrid ; the above table. (3) e) Note that the symbol <> means not equal to SET Type = Road WHERE Gears >= 20; SET Maker = Racer WHERE Type = Road ; WHERE Maker <> Racer ; the above table. (3) 5

6 Problems 3 - Challenging Example These questions will use the Tickets table shown on the right and combine everything you have learned so far. a) The SQL instructions below are executed on the above table. Each instruction modifies the table in some way. As you did in the previous set of questions, use the above copy of the Tickets table to note the changes made by each instruction. UPDATE Tickets SET SeasonTicket = 1488 WHERE Name = Bob AND Surname = Mortimer ; INSERT INTO Tickets VALUES (2655, Matthew, Phair, Junior,#31/03/2030#); UPDATE Tickets SET SeasonTicket = 1522, Type = Senior WHERE Name = Zac AND Surname = Allan ; the above table. (5) UPDATE Tickets SET Type = Junior WHERE SeasonTicket <= 3000; DELETE FROM Tickets WHERE SeasonTicket = 2999; b) A further SQL instruction is used to output a selected list of names from the modified table. Use your notes on the above Tickets table to complete the list of names the SQL instruction would produce as output. SELECT FirstName, Surname FROM Tickets WHERE Type = Junior AND Surname > M ; Expected Output FirstName Surname Cameron McKay Anna Smith Blair Malone Bob Mortimer Matthew Phair 2 marks for all correct, 1 mark for 1 error 6