LOOKUP(match-value, table-name, match-column, return-column)
LOOKUP() scans the table named by table-name for rows in which the value of the column named by match-column matches match-value, and returns the value of the column named by return-column from one of the matching rows.
match-value will be compared to values of the column named by match-column with = (equals). match-value will be interpreted with DECIMAL(), NUMBER(), or TEXT() as appropriate before comparison if its type differs from that of column match-column.
table-name, match-column, and return-column must be a literal Text values; they cannot be expressions.
Commonly, match-column and return-column are names that have special meanings to AppSheet internals, such as date, n, t, text, time, and others. Whenever AppSheet encounters such a name as literal, unquoted text, it may produce an error indicating the expression "could not be parsed due to exception: #VALUE!". To avoid or fix this problem, enclose the problematic text in quotes.
LOOKUP() is analogous to the VLOOKUP() formula in many spreadsheet applications.
The value from the column named by return-column from one arbitrarily-chosen row of those with a value matching match-value in the column named by match-column of the table named by table-name.