haskell-relational-record/examples.md

layout	title
default	Examples

Preparing

We assume that you have read both quick start and tutorial.

Schema of examples

We use the bank example in Learning SQL. Its support page provides a script to create the tables of the bank examples for MySQL. We modified it for SQLite and created a DB file called "examples.db" in the top directory of "relational-record-examples". We deeply thank Alan Beaulieu, the author of "Learning SQL".

Here is a list of tables copied from page 34 of "Learning SQL":

• Account -- a particular product opened for a particular customer
• Business -- a corporate customer (subtype of the Customer table)
• Customer -- a person or corporation known to the bank
• Department -- a group of bank employees implementing a particular banking function
• Employee -- a person working for the bank
• Individual -- a noncorporate customer (subtype of the Customer table)
• Officer -- a person allowed to transact business for a corporate customer
• Product -- a banking function offered to customers
• Product_type -- a group of products having similar function
• Transaction -- a change made to an account balance

The most of the following examples come from "Learning SQL", too. HRR code examples are found in "src/examples.hs".

Select

Descending sort order

SQL:

{% highlight sql %} SELECT account_id, product_cd, open_date, avail_balance FROM account ORDER BY avail_balance DESC; {% endhighlight %}

HRR:

{% highlight haskell %} account_3_7_1 :: Relation () Account account_3_7_1 = relation $ do a <- query account desc $ a ! Account.availBalance' return a {% endhighlight %}

Sorting via numeric placeholders

For backwards compatibility with the SQL92 version of standard, you can use numbers instead of names to specify the columns that should be sorted. With HRR you cannot use numbers for such purpose.

SQL:

{% highlight sql %} SELECT emp_id, title, start_date, fname, lname FROM employee ORDER BY 2,5; {% endhighlight %}

HRR: constructing new records in Applicative-like style.

{% highlight haskell %} employee_3_7_3 :: Relation () Employee1 employee_3_7_3 = relation $ do e <- query employee asc $ e ! Employee.title' asc $ e ! Employee.lname' return $ Employee1 |$| e ! Employee.empId' || e ! Employee.title' || e ! Employee.startDate' || e ! Employee.fname' || e ! Employee.lname'

data Employee1 = Employee1 { e1EmpId :: Int64 , e1Title :: Maybe String , e1StartDate :: Day , e1Fname :: String , e1Lname' :: String } deriving (Show)

$(makeRecordPersistableDefault ''Employee1) {% endhighlight %}

The order by clause

SQL:

SELECT open_emp_id, product_cd
FROM account
ORDER BY open_emp_id, product_cd;

HRR: TBD

Using the is null operator and the date literal

HRR supports date literal of the SQL standard, such like Date '2003-01-01'. However, SQLite has its own date literal without Date keyword, like this: '2003-01-01'. So, you have to define a function to support SQLite's date literal. Here we define 'unsafeSQLiteDayValue' function for that.

SQL:

SELECT *
FROM employee
WHERE end_date IS NULL AND (title = 'Teller' OR start_date < '2003-01-01');

HRR:

employee_4_1_2 :: Relation () Employee
employee_4_1_2 = relation $ do
  e <- query employee
  wheres $ isNothing (e ! Employee.endDate')
  wheres $ e ! Employee.title' .=. just (value "Teller")
     `or'` e ! Employee.startDate' .<. unsafeSQLiteDayValue "2003-01-01"
  return e

unsafeSQLiteDayValue :: SqlProjectable p => String -> p Day
unsafeSQLiteDayValue = unsafeProjectSqlTerms . showConstantTermsSQL

Another way, use a placeholder instead of a date literal. There is no need to define a helper function.

HRR: using placeholder

employee_4_1_2P :: Relation Day Employee
employee_4_1_2P = relation' $ do
  e <- query employee
  wheres $ isNothing (e ! Employee.endDate')
  (phDay,()) <- placeholder (\ph ->
    wheres $ e ! Employee.title' .=. just (value "Teller")
       `or'` e ! Employee.startDate' .<. ph)
  return (phDay, e) 

Range condition with the between operator

SLQ:

SELECT emp_id, fname, lname, start_date FROM employee
WHERE start_date
BETWEEN date('2001-01-01') AND date('2002-12-31');

HRR: TBD

Membership conditions

SQL:

SELECT account_id, product_cd, cust_id, avail_balance
FROM account
WHERE product_cd IN ('CHK', 'SAV', 'CD', 'MM');

HRR: returning raw rows.

account_4_3_3a :: Relation () Account
account_4_3_3a = relation $ do
  a  <- query account
  wheres $ a ! Account.productCd' `in'` values ["CHK", "SAV", "CD", "MM"]
  return a

HRR: constructing new records in Applicative-like style.

data Account1 = Account1
  { a1AccountId :: Int64
  , a1ProductCd :: String
  , a1CustId :: Int64
  , a1AvailBalance :: Maybe Double
  } deriving (Show)

$(makeRecordPersistableDefault ''Account1)

account_4_3_3aR :: Relation () Account1
account_4_3_3aR = relation $ do
  a  <- query account
  wheres $ a ! Account.productCd' `in'` values ["CHK", "SAV", "CD", "MM"]
  return $ Account1 |$| a ! Account.accountId'
                    |*| a ! Account.productCd'
                    |*| a ! Account.custId'
                    |*| a ! Account.availBalance'

Membership conditions using subqueries

SQL:

SELECT account_id, product_cd, cust_id, avail_balance
FROM account
WHERE product_cd IN (SELECT product_cd FROM product
WHERE product_type_cd = 'ACCOUNT');

HRR:

product_4_3_3b :: Relation String String
product_4_3_3b = relation' $ do
  p <- query product
  (phProductCd,()) <- placeholder (\ph -> wheres $ p ! Product.productTypeCd' .=. ph)
  let productCd = p ! Product.productCd'
  return (phProductCd, productCd)

account_4_3_3b :: Relation String Account
account_4_3_3b = relation' $ do
  a <- query account
  (phProductCd,p) <- queryList' product_4_3_3b
  wheres $ a ! Account.productCd' `in'` p
  return (phProductCd, a)

account_4_3_3bR :: Relation String Account1
account_4_3_3bR = relation' $ do
  a <- query account
  (phProductCd,p) <- queryList' product_4_3_3b
  wheres $ a ! Account.productCd' `in'` p
  let ar = Account1 |$| a ! Account.accountId'
                    |*| a ! Account.productCd'
                    |*| a ! Account.custId'
                    |*| a ! Account.availBalance'
  return (phProductCd, ar)

Using type holders:

run conn "ACCOUNT" account_4_3_3bR

Membership conditions using not in

SQL:

SELECT account_id, product_cd, cust_id, avail_balance
FROM account
WHERE product_cd NOT IN ('CHK', 'SAV', 'CD', 'MM');

HRR:

account_4_3_3c :: Relation () Account
account_4_3_3c = relation $ do
  a  <- query account
  wheres $ not' (a ! Account.productCd' `in'` values ["CHK", "SAV", "CD", "MM"])
  return a

Inner join

SQL:

SELECT e.fname, e.lname, d.name
FROM employee e INNER JOIN department d
USING (dept_id);

HRR:

join_5_1_2aT :: Relation () ((String, String), String)
join_5_1_2aT = relation $ do
  e  <- query employee
  d  <- query department
  on $ e ! Employee.deptId' .=. just (d ! Department.deptId')
  return $ e ! Employee.fname' >< e ! Employee.lname' >< d ! Department.name'

Complex join

SQL:

SELECT a.account_id, a.cust_id, a.open_date, a.product_cd
FROM account a INNER JOIN employee e ON a.open_emp_id = e.emp_id
INNER JOIN branch b ON e.assigned_branch_id = b.branch_id
WHERE e.start_date <= date('2004-01-01') AND
     (e.title = 'Teller' OR e.title = 'Head Teller') AND
     b.name = 'Woburn Branch';

HRR: TBD

Self-join

SQL:

SELECT e.fname, e.lname, e_mgr.fname mgr_fname, e_mgr.lname mgr_lname
FROM employee e INNER JOIN employee e_mgr
ON e.superior_emp_id = e_mgr.emp_id

HRR:

selfJoin_5_3aT :: Relation () ((String, String), (String, String))
selfJoin_5_3aT = relation $ do
  e  <- query employee
  m  <- query employee
  on $ e ! Employee.superiorEmpId' .=. just (m ! Employee.empId')
  let emp = e ! Employee.fname' >< e ! Employee.lname'
  let mgr = m ! Employee.fname' >< m ! Employee.lname'
  return $ emp >< mgr

####Sorting compound query results

SQL:

SELECT emp_id, assigned_branch_id
FROM employee
WHERE title = 'Teller'
UNION
SELECT open_emp_id, open_branch_id
FROM account
WHERE product_cd = 'SAV'
ORDER BY emp_id;

HRR:

employee_6_4_1a :: Relation () (Maybe Int64, Maybe Int64)
employee_6_4_1a = relation $ do
  e  <- query employee
  wheres $ e ! Employee.title' .=. just (value "Teller")
  return $ just (e ! Employee.empId') >< e ! Employee.assignedBranchId'

account_6_4_1a :: Relation () (Maybe Int64, Maybe Int64)
account_6_4_1a = relation $ do
  a  <- query account
  wheres $ a ! Account.productCd' .=. value "SAV"
  return $ a ! Account.openEmpId' >< a ! Account.openBranchId'

union_6_4_1a_Nest :: Relation () (Maybe Int64, Maybe Int64)
union_6_4_1a_Nest = relation $ do
  ea <- query $ employee_6_4_1a `union` account_6_4_1a
  asc $ ea ! fst'
  return ea

HRR:

union_6_4_1a_Flat :: Relation () (Maybe Int64, Maybe Int64)
union_6_4_1a_Flat = relation (do
    e  <- query employee
    wheres $ e ! Employee.title' .=. just (value "Teller")
    return $ just (e ! Employee.empId') >< e ! Employee.assignedBranchId'
  ) `union` relation (do
    a  <- query account
    wheres $ a ! Account.productCd' .=. value "SAV"
    return $ a ! Account.openEmpId' >< a ! Account.openBranchId'
  )

Grouping

SQL:

SELECT open_emp_id, COUNT(*) how_many
FROM account
GROUP BY open_emp_id
ORDER BY open_emp_id;

HRR:

group_8_1a :: Relation () (Maybe Int64, Int64)
group_8_1a = aggregateRelation $ do
  a  <- query account
  g  <- groupBy $ a ! Account.openEmpId'
  asc $ g ! id'
  return $ g >< count (a ! Account.accountId')

insert

TBD

update

TBD

delete

TBD