Select

Performs a query to retrieve data from a table.

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Methods

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selectDatabase()

→ (database = String) → this

Selects a different database for this query.

Parameters

Parameter	Type	Description
database	String	Name of the database to select

Returns

→ this

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distinct()

→ () → this

Ensures that only unique values are returned in the query results.

Returns

→ this

Example

Scenario: We want to get the EmployeeIDs of the Employees that have open orders in Orders

const empOrders = await instance.select("Orders", "EmployeeID") // Selects "EmployeeID" from "Orders"
                                .distinct() // Ensures unique EmployeeIDs
                                .execute();
console.log(empOrders);
/* Output:
[
    { EmployeeID: 5 },
    { EmployeeID: 6 },
    { EmployeeID: 4 },
    { EmployeeID: 3 },
    { EmployeeID: 9 },
    { EmployeeID: 1 },
    { EmployeeID: 8 },
    { EmployeeID: 2 },
    { EmployeeID: 7 }
]
*/

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where()

→ (string = String, values = Array<any>) → this

Adds a WHERE clause to filter results.

• Use ? as placeholders in the condition string to prevent SQL injection.
• If using joins, specify columns as table.column.

Parameters

Parameter	Type	Description
string	String	WHERE clause with ? placeholders for values.
values	Array<any>	Values to replace ?, in order.

Returns

→ this

Example

Scenario: We only want to get the Orders from the Customers with the id 90 and 34

const filteredOrders = await instance.select("Orders")  // Select "Orders" table
                                     .where("CustomerID = ? OR CustomerID = ?", [90, 34])
                                     .execute();
console.log(filteredOrders);
/* Output:
[
  { OrderID: 10248, CustomerID: 90, EmployeeID: 5, OrderDate: '1996-07-04', ShipperID: 3 },
  { OrderID: 10250, CustomerID: 34, EmployeeID: 4, OrderDate: '1996-07-08', ShipperID: 2 },
  { OrderID: 10253, CustomerID: 34, EmployeeID: 3, OrderDate: '1996-07-10', ShipperID: 2 }
]
*/

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having()

→ (string = String, values = Array<any>) → this

Same as .where(), but allows filtering after aggregation.

Parameters

Parameter	Type	Description
string	String	HAVING clause with ? placeholders..
values	Array<any>	Values to replace ?, in order.

Returns

→ this

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order()

→ (column = String, desc = Boolean, aggregation = Enum) → this

Adds sorting to the query.

Parameters

Parameter	Type	Description
column	String	Column to order by.
desc	Boolean	Sort in descending order? Defaults to false.
aggregation	Enum → MIN/MAX/COUNT/SUM/AVG	Optional aggregation function.

Returns

→ this

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count()

→ (doParse = Boolean) → this

Counts the number of rows in the first selected column.

Parameters

Parameter	Type	Description
doParse	Boolean	If true, returns a number instead of an array. Defaults to false.

Returns

→ this

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sum()

→ (doParse = Boolean) → this

Sums numerical rows of the first selected column.

Parameters

Parameter	Type	Description
doParse	Boolean	If true, returns a number. Defaults to false.

Returns

→ this

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avg()

→ (doParse = Boolean) → this

Calculates the average value of numerical rows in the first selected column.

Parameters

Parameter	Type	Description
doParse	Boolean	If true, returns a number. Defaults to false.

Returns

→ this

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group()

→ (...columns = String) → this

Groups rows by the specified columns.

Parameters

Parameter	Type	Description
...columns	String	Columns to group by.

Returns

→ this

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join()

→ (type = Enum, table = String, onOriginalColumn = String, onJoinedColumn = String, ...columns = String) → this

Performs a SQL JOIN.

Parameters

Parameter	Type	Description
type	Enum → LEFT/INNER/RIGHT/FULL OUTER	Type of join.
table	String	Table to join with.
onOriginalColumn	String	Column from the original table.
onJoinedColumn	String	Column from the joined table.
...columns	String	Columns to select.

Returns

→ this

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limit()

→ (number = Number, offset = Number) → this

Limits the number of returned rows and sets an offset.

Parameters

Parameter	Type	Description
number	Number	Maximum rows to return.
offset	Number	Offset for starting position.

Returns

→ this

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pagination()

→ (page = Number, itemsPerPage = Number) → this

Applies pagination to the query results.

Parameters

Parameter	Type	Description
page	Number	The page number (starting from 1).
itemsPerPage	Number	Number of items per page.

Returns

→ this

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execute()

async → () → Number / Array<Object>

Executes the query.

Returns

→ Number - if (doParse is true)
→ Array<Object> - Query Result

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