SQL_Blocks

1 - You can assemble a simple object that will then be converted into an SQL command:

a = Select('Actor') # --> SELECT * FROM Actor act

Note that an alias "act" has been added.

You can specify your own alias: a = Select('Actor a')

2 - You can also add a field, contains this...

• a = Select('Actor a', name=Field)

• Here are another ways to add a field:

  • Select('Actor a', name=Distinct )

  • Select('Actor a', name=NamedField('actors_name'))

  • Select( 'Actor a', name=NamedField('actors_name', Distinct) )

  2.1 -- Using expression as a field:

    Select(
        'Product',
        due_date=NamedField(
            'YEAR_ref',
            ExpressionField('extract(year from {f})') #  <<---
        )
    )

...should return: SELECT extract(year from due_date) as YEAR_ref...

3 - To set conditions, use Where:

• For example, a = Select(... age=gt(45) )

  Some possible conditions:

  • field=eq(value) - ...the field is EQUAL to the value;
  • field=gt(value) - ...the field is GREATER than the value;
  • field=lt(value) - ...the field is LESS than the value;

You may use Where.eq, Where.gt, Where.lt ... or simply eq, gt, lt ... 😉

3.1 -- If you want to filter the field on a range of values:

a = Select( 'Actor a', age=Between(45, 69) )

3.2 -- Sub-queries:

query = Select('Movie m', title=Field,
    id=SelectIN(
        'Review r',
        rate=gt(4.5),
        movie_id=Distinct
    )
)

>> print(query)

    SELECT
        m.title
    FROM
        Movie m
    WHERE
        m.id IN (
            SELECT DISTINCT r.movie
            FROM Review r WHERE r.rate > 4.5
        )

3.3 -- Optional conditions:

    OR=Options(
        genre=eq("Sci-Fi"),
        awards=contains("Oscar")
    )
    AND=Options(
        ..., name=contains(
            'Chris',
            Position.StartsWith
        )
    )

3.4 -- Negative conditions use the Not class instead of Where

based_on_book=Not.is_null()

3.5 -- List of values

hash_tag=inside(['space', 'monster', 'gore'])

4 - A field can be two things at the same time:

• m = Select('Movie m' release_date=[Field, OrderBy])
  • This means that the field will appear in the results and also that the query will be ordered by that field.
• Applying GROUP BY to item 3.2, it would look contains this:

  SelectIN(
      'Review r', movie=[GroupBy, Distinct],
      rate=Having.avg(gt(4.5))
  )
  

5 - Relationships:

    query = Select('Actor a', name=Field,
        cast=Select('Cast c', id=PrimaryKey)
    )

>> print(query)

SELECT
    a.name
FROM
    Actor a
    JOIN Cast c ON (a.cast = c.id)    

6 - The reverse process (parse):

text = """
        SELECT
                cas.role,
                m.title,
                m.release_date,
                a.name as actors_name
        FROM
                Actor a
                LEFT JOIN Cast cas ON (a.cast = cas.id)
                LEFT JOIN Movie m ON (cas.movie = m.id)
        WHERE
                (
                    m.genre = 'Sci-Fi'
                    OR
                    m.awards LIKE '%Oscar%'
                )
                AND a.age <= 69 AND a.age >= 45
        ORDER BY
                m.release_date DESC
"""

a, c, m = Select.parse(text)

6.1 --- print(a)

    SELECT
            a.name as actors_name
    FROM
            Actor a
    WHERE
            a.age <= 69
            AND a.age >= 45

6.2 --- print(c)

SELECT
        c.role
FROM
        Cast c

6.3 --- print(m)

SELECT
        m.title,
        m.release_date
FROM
        Movie m
WHERE
        ( m.genre = 'Sci-Fi' OR m.awards LIKE '%Oscar%' )
ORDER BY
        m.release_date DESC

6.4 --- print(a+c)

SELECT
        a.name as actors_name,
        cas.role
FROM
        Actor a
        JOIN Cast cas ON (a.cast = cas.id)
WHERE
        a.age >= 45
        AND a.age <= 69

6.5 --- print(c+m)

... or print(m+c)

SELECT
        cas.role,
        m.title,
        m.release_date,
        m.director
FROM
        Cast cas
        JOIN Movie m ON (cas.movie = m.id)
WHERE
        ( m.genre = 'Sci-Fi' OR m.awards LIKE '%Oscar%' )
        AND m.director LIKE '%Coppola%'
ORDER BY
        m.release_date,
        m.director

7 - You can add or delete attributes directly in objects:

• a(gender=Field)
• m.delete('director')

8 - Defining relationship on separate objects:

a = Select...
c = Select...
m = Select...

a + c => ERROR: "No relationship found between Actor and Cast"

8.1 - But...

a( cast=ForeignKey('Cast') )
c(id=PrimaryKey)

a + c => Ok!

8.2

c( movie=ForeignKey('Movie') )
m(id=PrimaryKey)

c + m => Ok!

m + c => Ok!

9 - Comparing objects

9.1

        a1 = Select.parse('''
                SELECT gender, Max(act.age) FROM Actor act
                WHERE act.age <= 69 AND act.age >= 45
                GROUP BY gender
            ''')[0]

        a2 = Select('Actor',
            age=[ Between(45, 69), Max ],
            gender=[GroupBy, Field]
        )       

a1 == a2 # --- True!

9.2

    m1 = Select.parse("""
        SELECT title, release_date FROM Movie m ORDER BY release_date 
        WHERE m.genre = 'Sci-Fi' AND m.awards LIKE '%Oscar%'
    """)[0]

    m2 = Select.parse("""
        SELECT release_date, title
        FROM Movie m
        WHERE m.awards LIKE '%Oscar%' AND m.genre = 'Sci-Fi'
        ORDER BY release_date 
    """)[0]

m1 == m2 # --- True!

9.3

best_movies = SelectIN(
    Review=Table('role'),
    rate=[GroupBy, Having.avg(gt(4.5))]
)
m1 = Select(
    Movie=Table('title,release_date'),
    id=best_movies
)

sql = "SELECT rev.role FROM Review rev GROUP BY rev.rate HAVING Avg(rev.rate) > 4.5"
m2 = Select(
    'Movie', release_date=Field, title=Field,
    id=Where(f"IN ({sql})")
)

m1 == m2 # --- True!

10 - CASE...WHEN...THEN

Select(
    'Product',
    label=Case('price').when(
        lt(50), 'cheap'
    ).when(
        gt(100), 'expensive'
    ).else_value(
        'normal'
    )
)

11 - optimize method

p1 = Select.parse("""
        SELECT * FROM Product p
        WHERE (p.category = 'Gizmo'
                OR p.category = 'Gadget'
                OR p.category = 'Doohickey')
            AND NOT price <= 387.64
            AND YEAR(last_sale) = 2024
        ORDER BY
            category
    """)[0]
    p1.optimize() #  <<===============
    p2 = Select.parse("""
        SELECT category FROM Product p
        WHERE category IN ('Gizmo','Gadget','Doohickey')
            and p.price > 387.64
            and p.last_sale >= '2024-01-01'
            and p.last_sale <= '2024-12-31'
        ORDER BY p.category LIMIT 100
    """)[0]
    p1 == p2 # --- True!

This will...

• Replace OR conditions to SELECT IN ...
• Put LIMIT if no fields or conditions defined;
• Normalizes inverted conditions;
• Auto includes fields present in ORDER/GROUP BY;
• Replace YEAR function with date range comparison.

The method allows you to select which rules you want to apply in the optimization...Or define your own rules!

NOTE: When a joined table is used only as a filter, it is possible that it can be changed to a sub-query:

query = Select(
    'Installments i', due_date=Field,  customer=Select(
        'Customer c', id=PrimaryKey,
        name=contains('Smith', Position.EndsWith)
    )
)
print(query)
print('-----')
query.optimize([RuleReplaceJoinBySubselect])
print(query)

SELECT
        i.due_date
FROM
        Installments i
        JOIN Customer c ON (i.customer = c.id)
WHERE
        c.name LIKE '%Smith'
-----
SELECT
        i.due_date
FROM
        Installments i
WHERE
        i.customer IN (SELECT c.id FROM Customer c WHERE c.name LIKE '%Smith')

12 - Adding multiple fields at once

    query = Select('post p')
    query.add_fields(
        'user_id, created_at',
        order_by=True, group_by=True
    )

...is the same as...

    query = Select(
        'post p',
        user_id=[Field, GroupBy, OrderBy],
        created_at=[Field, GroupBy, OrderBy]
    )

13 - Change parser engine

a, c, m = Select.parse(
    """
        Actor(name, id ?age = 40)
        <- Cast(actor_id, movie_id) ->
        Movie(id ^title)
    """,
    CypherParser
    # ^^^ recognizes syntax like Neo4J queries
)

print(a+c+m)

SELECT
        act.name,
        mov.title
FROM
        Cast cas
        JOIN Movie mov ON (cas.movie_id = mov.id)
        JOIN Actor act ON (cas.actor_id = act.id)
WHERE
        act.age = 40
ORDER BY
        mov.title

Separators and meaning:

• ( ) Delimits a table and its fields
• , Separate fields
• ? For simple conditions (> < = <>)
• <- connects to the table on the left
• -> connects to the table on the right
• ^ Put the field in the ORDER BY clause
• @ Immediately after the table name, it indicates the grouping field.
• $ For SQL functions like avg$field, sum$field, count$field...

detect function

It is useful to write a query in a few lines, without specifying the script type (cypher, mongoDB, SQL, Neo4J...)

Examples:

13.1 - Relationship

query = detect(
    'MATCH(c:Customer)<-[:Order]->(p:Product)RETURN c, p'
)
print(query)

output:

SELECT * FROM
    Order ord
    LEFT JOIN Customer cus ON (ord.customer_id = cus.id)
    RIGHT JOIN Product pro ON (ord.product_id = pro.id)

13.2 - Grouping

query = detect(
    'People@gender(avg$age?region="SOUTH"^count$qtde)'
)
print(query)

output:

SELECT
        peo.gender,
        Avg(peo.age),
        Count(*) as qtde
FROM
        People peo
WHERE
        peo.region = "SOUTH"
GROUP BY
        peo.gender
ORDER BY
        peo.qtde

13.3 - Many conditions...

    print( detect('''
        db.people.find({
            {
                $or: [
                    {status:{$eq:"B"}},
                    age:{$lt:50}
                ]
            },
            age:{$gte:18},  status:{$eq:"A"}
        },{
            name: 1, user_id: 1
        }).sort({
            user_id: -1
        })
    ''') )

output:

SELECT
        peo.name,
        peo.user_id
FROM
        people peo
WHERE
        ( peo. = 'B' OR peo.age < 50 ) AND
        peo.age >= 18 AND
        peo.status = 'A'
ORDER BY
        peo.user_id DESC

13.4 - Relations with same table twice (or more)

Automatically assigns aliases to each side of the relationship (In this example, one user invites another to add to their contact list)

    print( detect(
        'User(^name,id) <-Contact(requester,guest)-> User(id,name)'
       # ^^^ u1                                        ^^^ u2
    ) )

SELECT
        u1.name,
        u2.name
FROM
        Contact con
        RIGHT JOIN User u2 ON (con.guest = u2.id)
        LEFT JOIN User u1 ON (con.requester = u1.id)
ORDER BY
        u1.name

translate_to method

It consists of the inverse process of parsing: From a Select object, it returns the text to a script in any of the languages ​​below:

• QueryLanguage - default
• MongoDBLanguage
• Neo4JLanguage

14 - Window Function

Aggregation functions (Avg, Min, Max, Sum, Count) -- or Window functions (Lead, Lag, Row_Number, Rank) -- have the over method...

query=Select(
    'Enrollment e',
    payment=Sum().over(
        student_id=Partition, due_date=OrderBy,
        # _=Rows(Current(), Following(5)), 
           # ^^^-------> ROWS BETWEEN CURRENT ROW AND 5 FOLLOWING
        # _=Rows(Preceding(3), Following()),
           # ^^^-------> ROWS BETWEEN 3 PRECEDING AND UNBOUNDED FOLLOWING
        # _=Rows(Preceding(3)) 
           # ^^^-------> ROWS 3 PRECEDING
    ).As('sum_per_student')
)

...that generates the following query:

SELECT
        Sum(e.payment) OVER(
                PARTITION BY student_id
                ORDER BY due_date
        ) as sum_per_student
FROM
        Enrollment e

15 - The As method:

query=Select(
    'Customers c',
    phone=[
        Not.is_null(),
        SubString(1, 4).As('area_code', GroupBy)
    ],
    customer_id=[
        Count().As('customer_count', OrderBy),
        Having.count(gt(5))
    ]
)

You can use the result of a function as a new field -- and optionally use it in ORDER BY and/or GROUP BY clause(s):

SELECT
        SubString(c.phone, 1, 4) as area_code,
        Count(c.customer_id) as customer_count
FROM
        Customers c
WHERE
        NOT c.phone IS NULL
GROUP BY
        area_code HAVING Count(c.customer_id) > 5
ORDER BY
        customer_count

16 - Function classes

You may use this functions:

• SubString
• Round
• DateDiff
• Year
• Current_Date
• Avg
• Min
• Max
• Sum
• Count
• Lag
• Lead
• Row_Number
• Rank
• Coalesce
• Cast

Some of these functions may vary in syntax depending on the database. For example, if your query is going to run on Oracle, do the following:

Function.dialect = Dialect.ORACLE