Intro to tsql unit 2

Introduction To SQLUnit 2

Modern Business Technology

Introduction To TSQLUnit 2

Developed by

Michael Hotek

Unit 2

Goals• Limit result set with where• Use compound criteria• Grouping conditions• Comparison operators• Ranges• Wildcards• Escape characters• Pattern Matching• Negation

Where

• So far we have returned the entire contents of a table.

• This is usually not very practical

• Suppose we wanted to see the authors that live in California.

• We could do a select * from authors and scroll through the result set looking for those where state = CA

• While feasible for a small table, this is not practical.

Where

• So to limit the result set to just the data you need, we will use the third major SQL clause: where

• The where clause tells the database which rows to retrieve.

• To just retrieve those authors that live in CA, we would use the following:

• select au_lname, aufname, state from authors where state = 'CA'

au_lname au_fname state

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

White Johnson CA

Green Marjorie CA

Carson Cheryl CA

O'Leary Michael CA

...

(15 row(s) affected)

Compound Criteria

• This limited our result set to just those authors in CA

• But our list of authors could begin to get very large and we’re only looking for those authors with a last name of Green.

• We would do this with the following:

• select au_lname, au_fname, state from authors where state = 'CA' and lname = 'Green'


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

Green Marjorie CA

(1 row(s) affected)

Compound Criteria

• Make sure you are careful with the spelling. Our database is case insensitive, but this does not apply to the data values.

• Green does not equal GREEN

Compound Criteria

• Now that we know how to get just those authors who live in CA, how do we get the authors that live in KS also?

• We accomplish this through the use of an OR instead of an AND

• select * from authors where state = 'CA' or state = 'KS'


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

White Johnson CA

Green Marjorie CA

Carson Cheryl CA

O'Leary Michael CA

Straight Dean CA

Smith Meander KS

Bennet Abraham CA

Dull Ann CA

Gringlesby Burt CA

Locksley Charlene CA

...


Compound Criteria

• So, what is the difference between using an AND and an OR?

• The AND is exclusive– This means that the row must meet all of the

conditions in order to be selected

• The OR is inclusive– This means that for a row to be selected, it

has to meet just one of the criteria

Compound Criteria

• Now we are going to get a little more complicated.

• We want to select all authors who live in KS with a last name of Smith and also every author from CA.

• We know how to do the first part

• select au_lname, au_fname, state from authors where state = 'KS' and au_lname = 'Smith'

• We also know how to do the second part

• select au_lname, au_fname, state from authors where state = 'CA'

• We just need to put them together

• select au_lname, au_fname, state from authors where state = 'KS' and au_lname = 'Smith' or state = 'CA'


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

Smith George CA

White Johnson CA

Green Marjorie CA

Carson Cheryl CA

O'Leary Michael CA

Straight Dean CA

Smith Meander KS

Bennet Abraham CA

...


Compound Criteria

Grouping Criteria

• While this SQL statement returns the data we want, it isn’t very clear and is sloppy

• When using compound criteria in a where clause, you should always group the criteria to make it plain exactly what you want.

• You group by using parenthesis

• The proper SQL statement is as follows:

• select * from authors where (state = 'KS' and lname = 'Smith') or state = 'CA'

Comparisons

• Besides using an =, you can also use any of the other comparison operators: >, <, <=, >=.

• Suppose we want to return all of the books with a price greater than $10.00

select title_id, price from titles where price > 10

• We could also write: select title_id, price from titles where price >

$10.00title_id price

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

BU1032 19.99

BU1111 11.95

BU7832 19.99

MC2222 19.99

PC1035 22.95

PC8888 20.00

...


Comparisons

• One other thing you can take advantage of with comparison operators is that they don’t simply apply to numeric types of data.

• They can also be used on character data.

• To select all authors who live in states that come after MA we could use the following

select au_lname, state from authors where state > 'MA'

au_lname state

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

Greene TN

Blotchet-Halls OR

del Castillo MI

Panteley MD

Ringer UT

Ringer UT

(6 row(s) affected)

Range Output

• Suppose we want to select all authors who live in CA, MI, KS, and UT

• We could write the following:select au_lname, state from authors where

state = 'CA' or state = 'MI' or state = 'KS' or state = 'UT'

• With long lists, this get get very tedious and take a lot of typing.

• Fortunately, SQL gives us something much better

IN

• Instead of using multiple ORs, we can use an IN operator

select au_lname, state from authors where state in ('CA','KS','MI','UT')

• This will return the same listau_lname state

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

Smith CA

White CA

...

Straight CA

Smith KS

Bennet CA

...

Yokomoto CA

del Castillo MI

Stringer CA

...

McBadden CA

Ringer UT

Ringer UT


Range Output

• We now want to select all books that have a price greater than or equal to $10, but also less than or equal to $20.

• We could write the following:

select title_id, price from titles where price >= 10 and price <= 20

• But, there is a much simpler way

• SQL has given us a between operator

select title_id, price from titles where price between 10 and 20

Wildcards

• Sometimes we do not know exactly what we are looking for

• Or we are looking for the group of data that match a certain pattern

• In these cases we would use wildcards within our where clause

• SQL has two wildcard characters– The percent (%) symbol designates any

string of zero or more characters– The underscore (_) designates a single

character

Wildcards

• Suppose we wanted to select all authors whose first names start with M

select au_fname, au_lname from authors where au_fname like 'M%'

au_fname au_lname

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

Marjorie Green

Michael O'Leary

Meander Smith

Morningstar Greene

Michel DeFrance

(5 row(s) affected)

Wildcards

• Maybe we want to select all of the authors whose first name is Carl.

• We have to be careful here, because it could be spelled Carl or Karl

select au_fname, au_lname from authors where au_fname like '_arl'

au_fname au_lname

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

Carl Burns

Karl Johnson

(2 row(s) affected)

Wildcards

• You can combine wildcards to retrieve exactly what you need

• Suppose we needed to retrieve all of the Smiths in the database

• The last name could be spelled Smith, Smithe, or Smythe. We want to retrieve all of the spellings

select au_fname, au_lname from authors where au_lname like 'Sm_th%'

au_fname au_lname

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

Meander Smith

Jim Smithe

Patti Smythe

(3 row(s) affected)

Escape characters

• But what happens when we really want to find a % inside of the data

• To find this data we will employ an escape character

select notes from titles where notes like '%@%%' escape '@'

• This tells the DBMS to treat the next character after the escape character (@) as a literal string

notes

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

What happens when the data runs dry?%

(1 row(s) affected)

Pattern Matching

• But what do we do when we know what we are looking for, but know it could have many variations.

• We can employ a technique called pattern matching

• This technique can mix wildcards with sets of characters that required to be present

• These are designated within brackets inside of the string we are matching

Pattern Matching

• Suppose we wanted to retrieve all of the authors whose last names started with either an L, M, or S

select au_lname, au_fname from authors where au_lname like '[LMS]%'

au_lname au_fname

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

Locksley Charlene

MacFeather Stearns

McBadden Heather

Smith George

Smith Meander

Smithe Jim

Smythe Patti

Straight Dean

Stringer Dirk

(9 row(s) affected)

Pattern Matching

• Suppose we want to retrieve all five letter first names where only the first character is uppercase

• We do not want to retrieve name names like McDay

• We also don't want names with special characters like apostrophes

select au_lname, au_fname from authors where au_lname like '[A-Z][a-z][a-z][a-z]'

au_lname au_fname

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

Dull Ann

(1 row(s) affected)

Pattern Matching

• We want to retrieve all books with a title of Life Without Fear, but don't know how the word without was stored (uppercase, lowercase, or mixed case)

select title_id, titles from titles where title

like '%[Ww][Ii][Tt][Hh][Oo][Uu][Tt]%'title_id title

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

PS2106 Life Without Fear

(1 row(s) affected)

Pattern Matching

• We now want to retrieve just those authors whose first name is four characters long

select au_lname, au_fname from authors where au_fname like '____' (That's four underscore characters)

au_lname au_fname

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

Burns Carl

Gringlesby Burt

Johnson Karl

Ringer Ann

Straight Dean

Stringer Dirk

(6 row(s) affected)

Pattern Matching

• But you ask, why do we see the entry for Ann in this list. It only has three characters.

• This is for two reasons– There was a space added to the end– Depending on how the database was set

up, it could pad spaces on to the end (Beyond scope)

Pattern Matching

• To get around this we exclude the space

select * from authors where au_fname

like '[^ ] [^ ] [^ ] [^ ]'au_id au_lname au_fname

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

111-11-1112 Burns Carl

111-11-1113 Johnson Karl

274-80-9391 Straight Dean

472-27-2349 Gringlesby Burt

724-08-9931 Stringer Dirk

(5 row(s) affected)

• The caret is a negation operator. The query above says to retrieve any first names that do not have a space as one of the four characters

Pattern Matching

• Granted, in most real world situations you will not go to these lengths when retrieving data.

• But constructs like this are used extensively to ensure only valid data is entered into tables

• Rules and constraints are beyond the scope of this unit, but the examples below are for demonstrative purposes to give an idea of further applications to pattern matching

Pattern Matching

• Suppose you have a column that will accept 6 characters

• You have to be careful, because numbers and special characters like #,@,& will also go in this column

• To restrict this to just characters, use the following

[A-z] [A-z] [A-z] [A-z] [A-z] [A-z]

Real World Example

• A table we are working with stores social security numbers (complete with dashes)

'[0-9] [0-9] [0-9]- [0-9] [0-9]- [0-9] [0-9]

[0-9] [0-9]'

• Vehicle VIN numbers have a very specific format that conforms to the following VIN: 1G2JB14KOL7569785

' [0-9][A-Z] [0-9][A-Z][A-Z] [0-9] [0-9][A-Z][A-Z][A-Z] [0-9] [0-9] [0-9] [0-9] [0-9] [0-9] [0-9] '

Negation

• We briefly touched on negation a few slides before.

• The negation operator is NOT or in patterns a caret (^)

Negation

• In a query above we extracted all four letter first names that did not have a space in them.

• Now we want to extract everything but these names

select au_fname, au_lname from authors where au_fname not like '[^ ] [^ ] [^ ] [^ ]'

au_fname au_lname

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

Abraham Bennet

Reginald Blotchet-Halls

Carl Burns

Cheryl Carson

Michel DeFrance

Ann Dull

Marjorie Green

Morningstar Greene

Burt Gringlesby

Sheryl Hunter

Karl Johnson

Livia Karsen

...


Negation

• Select all authors who do not live in CA

select * from authors where state <> 'CA'

• Depending on DBMS, this can also be written as

select au_fname, au_lname from authors

where state != 'CA'au_fname au_lname state

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

Carl Burns MA

Karl Johnson MA

Patti Smythe MA

Jim Smithe MA

Meander Smith KS

Morningsta Greene TN

Reginald Blotchet-Halls OR

Innes del Castillo MI

Michel DeFrance IN

Sylvia Panteley MD

Anne Ringer UT

Albert Ringer UT


Review

• A where clause allows us to restrict the result set

• We can combine multiple criteria in a single where clause using and/or

• We can use comparison operators to specify ranges of data

• IN allows us to easily specify a list of values to find

• Between simplifies some range searches and is inclusive (The value specified as the upper and lower bound is also retrieved)

• We can use % and _ as wildcards to do sophisticated searching

• We can use an escape character to cause SQL to ignore a wildcard and treat as a literal

• These can be combined with pattern matching to specify very specific patterns of data

• We can negate our searching by using not, ^, <>, or !=

Unit 2 Exercises

• Time allotted is 30 minutes

Intro to tsql unit 2

Technology

Transcript of Intro to tsql unit 2