sqlCol

Syntax

sqlCol(colName, [func], [alias], [qualifier])

Arguments

colName is a string scalar/vector indicating column name(s).

func is a unary function. It is optional.

alias is a string scalar/vector indicating column name(s) of the selected column(s) or calculation result(s).

qualifier is a STRING scalar. It is only used in a table join operation when we need to select a column that appears in both tables and that is not a matching column. It indicates the table from which to select the column.

Details

Generate metacode for selecting one or multiple columns with or without calculations. It is generally used together with function sql and eval to generate SQL statements dynamically.

Examples

$ t = table(`GME`AMC`KOSS as symbol, 325 13.26 64 as price);
$ colName="symbol";
$ sql(select=sqlCol(colName), from=t).eval();

symbol
GME
AMC
KOSS

$ colName="price";
$ sql(select=sqlCol(colName, max, `maxPrice), from=t).eval();

maxPrice
325

$ t1 = table(1 2 3 3 as id, 7.8 4.6 5.1 0.1 as value, 4 3 2 1 as x);
$ t2 = table(5 3 1 as id,  300 500 800 as qty, 44 66 88 as x) ;
$ sql(select=(sqlCol(`id),sqlCol(colName=`x, alias="t1_x", qualifier="t1"),sqlCol(colName=`x, alias="t2_x", qualifier=`t2)), from=<ej(t1,t2,`id)>).eval()

id	t1_x	t2_x
1	4	88
3	2	66
3	1	66