SELECT

Contents

• Supported clauses
  • Example per clause
• Two forms of select statements
• Table aliasing
• Sub-query

SELECT statement is used to retrieve records from one or more tables in PostgreSQL.
More about SELECT statement can be found at:
PostgreSQL - https://www.postgresql.org/docs/11/sql-select.html
MySQL - https://dev.mysql.com/doc/refman/8.0/en/select.html
MariaDB - https://mariadb.com/kb/en/library/select/

Supported clauses

• SELECT(expressions...) - expressions to form output rows of the SELECT statement.
• OPTIMIZER_HINTS(hints...) - provides a way to optimize query execution per-statement basis (MySQL only)
• DISTINCT() - remove all duplicate rows from result set
• FROM(tableSource...) - specifies one or more source tables for the SELECT.
• WHERE(condition) - only rows for which condition returns true will be selected.
• GROUP BY(groupingElement, ...) - will condense into a single row all selected rows that share the same values for the grouped expressions.
• HAVING(condition) - eliminates group rows that do not satisfy the condition
• WINDOW(name) - starts composing name window definition
• ORDER BY(orderBy, ...) - causes the result rows to be sorted according to the specified expression(s)
• LIMIT(count) - specifies the maximum number of rows to return
• OFFSET(start) - specifies the number of rows to skip before starting to return rows
• FOR(lockMode) - how SELECT will lock rows as they are obtained from the table
  PostgreSQL lock mode can be: UPDATE(), NO_KEY_UPDATE(), SHARE() and KEY_SHARE(), with optional clauses: NOWAIT() and SKIP_LOCKED().
  MySQL lock modes can be: UPDATE() and SHARE(), with optional clauses: NOWAIT() and SKIP_LOCKED().
• UNION(select) / UNION_ALL(select) - computes the set union of the rows returned by the involved SELECT statements
• INTERSECT(select) / INTERSECT_ALL(select) - computes the set intersection of the rows returned by the involved SELECT statements
• EXCEPT(select) / EXCEPT_ALL(select) - computes the set of rows that are in the result of the left SELECT statement but not in the result of the right one

This list might be extended with feature Jet releases.

Example per clause

SELECT clause

Sample SELECT clause written in Go:

   // dot "." import implied
   SELECT(
        Int(1).ADD(Int(12)).SUB(Int(21)),                           // arbitrary expression
        Film.Name,                                                  // column
        Customer.FirstName.CONCAT(Customer.LastName).AS("FullName") // alias
   )

Above SQL clause in go will produce following raw SQL:

SELECT 1 + 12 - 21,
       film.name AS "film.name",  
       customer.first_name || customer.last_name AS "FullName"                                  

film.name AS "film.name" - column names are aliased by default. Alias is used during execution to map row result to appropriate model structure.

OPTIMIZER_HINTS (MySQL only)

SELECT(Actor.ActorID).
OPTIMIZER_HINTS(MAX_EXECUTION_TIME(1), QB_NAME("mainQueryBlock"), "NO_ICP(actor)")

SELECT /*+ MAX_EXECUTION_TIME(1) QB_NAME(mainQueryBlock) NO_ICP(actor) */ actor.actor_id AS "actor.actor_id"

DISTINCT clause

// Go:

SELECT(Film.Name).
DISTINCT().

// PostgreSQL only
SELECT(Film.Duration, Film.Rating, Film.Name).
DISTINCT(Film.Duration, Film.Rating)

-- SQL:

SELECT DISTINCT film.name AS "film.name"

// PostgreSQL only
SELECT DISTINCT ON (film.duration, film.rating) 
     film.duration AS "film.duration"
     film.rating AS "film.rating"
     film.name AS "film.name"

FROM clause

The FROM clause specifies one or more source tables for the SELECT.

Go:
1) .FROM(Film)
2) .FROM(
      Film.
        INNER_JOIN(Language, Langauge.LanguageID.EQ(Film.FilmID))
   )
3) .FROM(Film, Language, Artist) // implicit CROSS JOIN

SQL:
1) FROM dvds.film
2) FROM Film 
       INNER JOIN Language ON (Language.LanguageID = Film.FilmID)
3) FROM Film, Language, Artists

WHERE clause

Go:
.WHERE(Film.Length.GT(Int(150)))

SQL:
WHERE film.length > 150

GROUP BY clause

Go:
1) .GROUP_BY(Film.Length)
// postgres
2) .GROUP_BY(
	GROUPING_SETS(
		WRAP(Inventory.FilmID, Inventory.StoreID),
		WRAP(Inventory.FilmID),
		WRAP(),
	),
   )
3) .GROUP_BY(
	CUBE(Country.Country, City.City),
   )
4) .GROUP_BY(
	ROLLUP(Country.Country, City.City),
   )
// mysql
5) .GROUP_BY(
	WITH_ROLLUP(Inventory.FilmID, Inventory.StoreID),
)	

SQL:
1) GROUP BY film.length
-- postgres
2) GROUP BY GROUPING SETS((inventory.film_id, inventory.store_id), (inventory.film_id), ())
3) GROUP BY CUBE(country.country, city.city)
4) GROUP BY ROLLUP(country.country, city.city)
-- mysql
5) GROUP BY inventory.film_id, inventory.store_id WITH ROLLUP

WINDOW

SELECT(
    AVG(Payment.Amount).OVER(),
    MINf(Payment.Amount).OVER(PARTITION_BY(Payment.CustomerID).ORDER_BY(Payment.PaymentDate.DESC())),
    ROW_NUMBER().OVER(Window("w1")),
    RANK().OVER(
       Window("w2").
       ORDER_BY(Payment.CustomerID).
       RANGE(PRECEDING(UNBOUNDED), FOLLOWING(UNBOUNDED)),
    ),
    AVG(Payment.Amount).OVER(Window("w3").ROWS(PRECEDING(1), FOLLOWING(2))),
).
FROM(Payment).
WINDOW("w1").AS(PARTITION_BY(Payment.PaymentDate)).
   WINDOW("w2").AS(Window("w1")).
   WINDOW("w3").AS(Window("w2").ORDER_BY(Payment.CustomerID)).

SELECT AVG(payment.amount) OVER (),
     MIN(payment.amount) OVER (PARTITION BY payment.customer_id ORDER BY payment.payment_date DESC),
     ROW_NUMBER() OVER (w1),
     RANK() OVER (w2 ORDER BY payment.customer_id RANGE BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING),
     AVG(payment.amount) OVER (w3 ROWS BETWEEN 1 PRECEDING AND 2 FOLLOWING)
FROM dvds.payment
WINDOW w1 AS (PARTITION BY payment.payment_date), w2 AS (w1), w3 AS (w2 ORDER BY payment.customer_id);

HAVING clause

Go:
.HAVING(SUMi(Film.Length).GT(Int(150))

SQL:
HAVING SUM(film.length) > 150

ORDER BY clause

Go:
.ORDER_BY(Film.Length)

SQL:
ORDER BY film.length

LIMIT clause

Go:
.LIMIT(11)

SQL:
LIMIT 11

OFFSET clause

Go:
.OFFSET(11)

SQL:
OFFSET 11

FOR clause

Go:
.FOR(NO_KEY_UPDATE().SKIP_LOCKED())

SQL:
FOR NO KEY UPDATE SKIP LOCKED

10. Set clauses (UNION, UNION_ALL, INTERSECT, INTERSECT_ALL, EXCEPT, EXCEPT_ALL)

Go:
SELECT(Payment.Amount).FROM(Payment)
UNION_ALL(SELECT(Payment.Amount).FROM(Payment))

Sql:
(
     SELECT payment.amount AS "payment.amount"
     FROM dvds.payment
)
UNION
(
     SELECT payment.amount AS "payment.amount"
     FROM dvds.payment
);

Two forms of select statements

1. Classical select statement

Columns selected are before table sources(FROM clause)

SELECT(
    Payment.AllColumns,
    Customer.AllColumns,
).
FROM(
    Payment.
        INNER_JOIN(Customer, Payment.CustomerID.EQ(Customer.CustomerID)),
).
ORDER_BY(Payment.PaymentID.ASC()).
LIMIT(30)

2. Jet select statement

Table sources are before columns selected. There is no FROM clause.

Payment.
    INNER_JOIN(Customer, Payment.CustomerID.EQ(Customer.CustomerID))
SELECT(
    Payment.AllColumns,
    Customer.AllColumns,
).
ORDER_BY(Payment.PaymentID.ASC()).
LIMIT(30)

Note

Jet form is added, because sometimes feels more natural to first think about the tables of interest, and then about the columns. Although the second form feels more natural, the first form is preferred because it looks and feels more like a native SQL.
Both forms produce exactly the same raw SQL.

Table aliasing

// alias first
manager := Employee.AS("Manager")

// then aliased table can be used in a statement
stmt := SELECT(
	manager.AllColumns,
).FROM(
	manager,
)

SELECT "Manager"."EmployeeId" AS "Manager.EmployeeId",
     "Manager"."LastName" AS "Manager.LastName",
     "Manager"."FirstName" AS "Manager.FirstName",
     "Manager"."Title" AS "Manager.Title",
FROM chinook."Employee" AS "Manager";

Note that model.Employee can not be used as a destination for this query. Expected destination type name is now Manager.
To use generated model types with aliased tables there are two options:

1. Define new type

type Manager model.Employee
var dest Manager

err := stmt.Query(db, &dest)

2. Field aliasing

var dest struct {
    Manager model.Employee `alias:"Manager.*"`
}

err := stmt.Query(db, &dest)