As-of join

Where

• t1 is a table
• t2 is a simple table
• c1…cn is a symbol list of column names, common to t1 and t2, and of matching type
• column cn is of a sortable type (typically time)

returns a table with records from the left-join of t1 and t2. In the join, columns c1…cn-1 are matched for equality, and the last value of cn (most recent time) is taken. For each record in t1, the result has one record with the items in t1, and

• if there are matching records in t2, the items of the last (in row order) matching record are appended to those of t1;
• otherwise the remaining columns are null.

aj, aj0

aj and aj0 return different times in their results:

aj    boundary time from t1
aj0   actual time from t2