How to perform SQL "SELECT SUM(item.cost * item.amount)... " query - kotlin

Question

im trying to write equivalent of SQL query:
SELECT tax.name as tax, SUM(item.cost * item.amount) as total FROM Invoices inv
JOIN InvoiceItems item ON( item.invoice = inv.id )
JOIN Taxes tax ON( tax.id = it.tax )
WHERE inv.id = 1
GROUP BY tax.id
I can't figure out how to "add" total column to the query, my code is as follows
val res = Invoices
.innerJoin(InvoiceItems, { Invoices.id }, { InvoiceItems.invoice })
.innerJoin(Taxes, { InvoiceItems.tax }, { Taxes.id })
.slice( Taxes.name.alias("tax"), InvoiceItems.cost, InvoiceItems.amount )
.select { Invoices.id eq 1 }
Is it even possible to do it this way or i have to do it later in code?

Answer 1

You can use TimesOp within Expression.build{} block, like this:
val total = Expression.build { Invoices.cost * Invoices.amount }
val taxAndTotal = Invoices.innerJoin(InvoiceTaxes).innerJoin(Taxes)
.slice(Taxes.name, total)
.select{ Invoices.id eq 1 }
.groupBy(Taxes.id)
.map { it[Taxes.name] to it[total] }

Answer 2

I did not find how can we use times like InvoiceItems.cost times InvoiceItems.amount, but you can construct your own TimesOp object like this:
val taxAlias = Taxes.alias("tax")
val itemAlias = InvoiceItems.alias("item")
val invoiceAlias = Invoices.alias("inv")
println(invoiceAlias
.innerJoin(itemAlias, { invoiceAlias[Invoices.id] }, { itemAlias[InvoiceItems.invoice] })
.innerJoin(taxAlias, { itemAlias[InvoiceItems.tax] }, { taxAlias[Taxes.id] })
.slice(
taxAlias[Taxes.name].alias("tax"),
TimesOp(
itemAlias[InvoiceItems.cost],
itemAlias[InvoiceItems.amount],
InvoiceItems.amount.columnType
).sum().alias("total"))
.select { invoiceAlias[Invoices.id] eq 1 }
.groupBy(taxAlias[Taxes.id])
.prepareSQL(QueryBuilder(false))
)
Outputs the following sql for h2 syntax:
SELECT TAX.NAME tax, SUM((ITEM.COST) * (ITEM.AMOUNT)) total FROM INVOICES inv
INNER JOIN INVOICEITEMS item ON INV.ID = ITEM.INVOICE
INNER JOIN TAXES tax ON ITEM.TAX_ID = TAX.ID
WHERE INV.ID = 1
GROUP BY TAX.ID