union@"union"
The "union" command creates a new table which contains all
or selected columns from two source tables. The resultant
table contains all rows from each source table.
When rows from the two tables
match in all common columns, a single resultant row is created.
When rows from the two tables do not
match in all common columns, a resultant row is created
for each source row, with missing values filling out the rows.
missing value
<"union" <table-1> "with" <table-2> "forming" <table-3> "+"
〈"using" <column-1> <column-2> ...〉
creates <table-3> from the union of <table-1> and <table-2>.