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Databases Semester 2Week 1 Lab 2

The Delete, grant, revoke and Select Statements

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Firstly…

• Finish lab 1.– You will now have two joined tables.

• VERY IMPORTANT!– If you get an error, SAVE IT in an

ERROR.TXT file. When you find out what it means, type the explanation below it in the ERROR.TXT file. This way, if you come across it again, you’ll know what it means.

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Next…

• Populate the tables.

• The following two slides give a sample of what could be in the tables.

• You need not use these values, but you must keep the values appropriate to the subject.

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Supplier table

SupplierId SName

1001 ‘Chunky Choc’

1002 ‘Juicy Jellies’

1003 ‘Crunchy crisps’

1004 ‘Fizzy drinks’

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Product tableProductCode

ProductName ProductPrice

SupplierId

TCHO Cheese&Onion €.80 1003

TSVN Salt&Vinegar €.80 1003

SOUR Juicy Sours €.75 1002

TBUF Buffalo Crisps €.80 1003

PSTS Fruit Pastilles 50g €.55 1002

COLA Cola flavoured €1.00 1004

LMON Lemonade €1.00 1004

CLAL Large Cola 1litre €1.50 1004

ORNG Orange flavoured €1.00 1004

PSTL Fruit Pastiles 150g €1.50 1002

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Deleting a row

• First try one that has no dependants.Look at the example. If you are using this, then one of the suppliers has no products.

SQL> delete from supplier where supplierId = <you decide>;

1 row deleted.

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Try to delete a row with dependants

• Attempt to delete the supplier row with supplierID 1003

SQL> delete from supplier where supplierId = 1003*ERROR at line 1: ORA-02292: integrity constraint

(POBYRNE.SUPPLIER) violated - child record found

• Because, there is one or more products depending on it:

SQL> select * from product where supplierId = 1003;PRODUCTCODE PRODUCTNAME PRODUCTPRICE SUPPLIERID----------- ----------- ------------ ----------TCHO Cheese&Onion 0.8000000 1003TSVN Salt&Vinegar 0.8000000 1003TBUF Buffalo Crisps 0.8000000 1003

• As with DROP, you cannot delete a row if rows in other tables depend on it.

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Updating

• The Supplier called ‘Juicy Drinks’ has raised the price of all products by 10%.

• Update the price for the appropriate rows in the table.–See lecture week 1 semester 2.

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Granting / revoke access• To grant access to another user:

– Connect to your schema• I connected to builder

– Enter a ‘grant’ for each object.

• I granted each of you access to the tables in the builder schema.

• For a student with a schema called jbloggs in the ft228 database, I entered the following: grant select on customer to jbloggs;grant select on supplier to jbloggs;grant select on staff to jbloggs;grant select on corder to jbloggs;etc.

• To reverse this:– Revoke select on customer from jbloggs;

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Using a table from a different schema

• Any student who has been granted access to the table stock in the schema builder:–Select * from builder.stock;– The builder. Prefix tells the DBMS that

you are looking outside your own schema.

– SEE EXERCISE SLIDE AT THE END.

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Simple selects

• The full syntax of the SELECT statement is complex, but the main clauses can be summarized as:

• SELECT select_list[INTO new_table_name]FROM table_list[WHERE search_conditions][GROUP BY group_by_list][HAVING search_conditions][ORDER BY order_list [ASC | DESC] ]

• In this lesson, we will address only those clauses in black.

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Select list

• Describes the columns of the result set. It is a comma-separated list of expressions.

• Each expression defines both – the format (data type and size) and – the source of the data for the result set column.

• Each select list expression is usually a reference to a column in the source table or view the data is coming from, but can be any other expression, such as a constant or a Transact-SQL function.

• Using the * expression in a select list specifies that all columns in the source table are returned.

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FROM table_list

• Contains a list of the tables from which the result set data is retrieved. These sources can be: – Base tables or views in your own schema.– Base tables or views in schemae to which you

have select access.

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Simplest select

• Select * from <table-name>• E.g. Select * from builder.corderline;

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WHERE search_conditions• The WHERE clause is a filter that defines the conditions each row

in the source tables must meet to qualify for the SELECT. • Only rows that meet the conditions contribute data to the result set. • Data from rows that do not meet the conditions are not used.

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Selection

• Selection picks individual columns from a table:

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Projection

• Projection picks only rows that satisfy a condition:SQL> select * from stock where stock_description like '%block%';STOCK STOCK_DESCRIPTION UNIT_PRICE UNITCOSTPRICE STOCK_LEVEL

REORDER_LEVEL----- -------------------- ---------- ------------- -----------

-------------SUPPLIER_ID-----------A101 Cavity blocks(100) 200 500 300

100 501E101 Cavity blocks(500) 1000 500 172

200 501E141 Cavity blocks(200) 400 130 300

200 501SQL>

• Note that each row wraps around, making it difficult to read.

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Conditions

• And, or not

• Equal, not equal, greater than, less than.

• Like, using % and –– % is a wildcard string of any length– - is a single wildcard character;

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Using likeSQL> select stock_code from stock where stock_code like

'_1%‘;STOCK-----A101A111B101B111C101C121D101D131E101E14110 rows selected.

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Using like and underscore

SQL> select stock_code from stock where stock_code like '_1__‘;

STOCK-----A101A111B101B111C101C121D101D131E101E141

10 rows selected.

• Note the change in position of the ‘1’:

SQL> select stock_code from stock where stock_code like '__1_‘;

STOCK

-----

A111

B111

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CatalogSQL> select * from cat;

TABLE_NAME TABLE_TYPE------------------------------ -----------BIN$diXeGjXrQFi1kU/+ypNLsQ==$0 TABLEBIN$6btY4yriRdic8z2ONHRQrg==$0 TABLEBIN$Suh8BiYvRGuAAEdTnfho0w==$0 TABLEBIN$4DwYo9kfTciwcX3xGgcz3A==$0 TABLECUSTOMER TABLECORDER TABLESUPPLIER TABLESTOCK TABLESORDERLINE TABLESTAFF TABLESORDER TABLE

TABLE_NAME TABLE_TYPE------------------------------ -----------CORDERLINE TABLEBIN$CW8kb+b3Q+WljFuHIBZosQ==$0 TABLEBIN$Jb8z6PBiTL6Hy8yXBB8W3g==$0 TABLEBIN$5AZXhMuMS4mosvy8TqkfqQ==$0 TABLEBIN$hkvkMrD9RrqOMe4W2key9g==$0 TABLEBIN$pFcvgvUlSDmjAyQPR5Gz7A==$0 TABLEBIN$Pk3/ceHkRvOH06D3q/6WeA==$0 TABLEBIN$kZs92llMTwKdMcBRyIwlbg==$0 TABLEBIN$L4P807SFTNm63jXRmPA7XA==$0 TABLEBIN$oV13pVZNQr+ow/hMlzjzww==$0 TABLEBIN$K4j8mchgSh6CseBlwvlJxw==$0 TABLE

TABLE_NAME TABLE_TYPE------------------------------ -----------BIN$w54kQhBiQciAp90csiFiWw==$0 TABLEBIN$E+DmYcaIQxiLOa0euxpTaA==$0 TABLEBIN$WtulD5u9T2CdH/eYXdC6PQ==$0 TABLEBIN$sUogRgsJT221fbL/tFGcCw==$0 TABLEBIN$gCyduUbEQrOk1DVLgPpr2Q==$0 TABLEBIN$/uY2loJiTGu3UFW+NjUBxQ==$0 TABLEBIN$lv9wTq5gRmGK2th8kl4hnw==$0 TABLE

29 rows selected.

• This is unclear and unhelpful. We don’t want to see the dropped tables. See following slide.

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Only get the current tables:

SQL> select * from cat where table_name not like 'BIN$%‘;

TABLE_NAME TABLE_TYPE

------------------------------ -----------

CUSTOMER TABLE

CORDER TABLE

SUPPLIER TABLE

STOCK TABLE

SORDERLINE TABLE

STAFF TABLE

SORDER TABLE

CORDERLINE TABLE

8 rows selected.

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Miscellaneous

• To denote a string, use single quotes. Double quotes are not recognised.

• If you want to embed a single quote (i.e. an apostrophe!) in a string, precede it with another single quote (see slide 3 for example) .– Note: If you copy single quotes from word, they

don’t work, but they work from Notepad.• You do not need to use quotes for numeric fields:

– Select * from Product where UnitPrice <5

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Sorting

• The order by clause will allow you to sort the fields.

• The default order is ascending. To change it to descending, use the keyword desc.

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Select without ordering

SQL> select * from corderline;

QUANTITYREQUIRED CORDERNO STOCK---------------- ---------- ----- 20 101 A101 47 103 B111 1 103 C101 3 103 C121 1 105 D101 2 107 D131 2 103 E101 5 108 E101 200 101 BRK11 20 106 A111

10 rows selected.

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Select with orderingSQL> select * FROM CORDERLINE ORDER BY STOCK_CODE;

QUANTITYREQUIRED CORDERNO STOCK---------------- ---------- ----- 20 101 A101 20 106 A111 47 103 B111 200 101 BRK11 1 103 C101 3 103 C121 1 105 D101 2 107 D131 2 103 E101 5 108 E10110 rows selected.

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Reversing the order:SQL> select * from corderline order by stock_code

desc;QUANTITYREQUIRED CORDERNO STOCK

---------------- ---------- -----

2 103 E101

5 108 E101

2 107 D131

1 105 D101

3 103 C121

1 103 C101

200 101 BRK11

47 103 B111

20 106 A111

20 101 A101

10 rows selected.