Hi,
Mapping Load: The mapping prefix is used on a load or select statement to create a mapping table, these tables are different from other tables. They will be stored in separate area of memory and used as mapping tables during script execution. After execution they will automatically drop.
Ex. Mapping (Load Statement/Select Statement)
Apply Map: used for mapping data from one source to another at load time.
Ex. Apply map (‘Mapname’, expr,[default expr])
applymap: it is used to add the fields to our table with the help of other table . It is used as joins. The main diff between join and apply map is : If we have to add multiple fields i prefer join if we have to add one or two fields I prefer apply map
Mapping: The mapping prefix is used to create a mapping table that can be used for e.g. replacing field values and field names during the script run.
Preceding Load:
The preceding LOAD feature allows you to load a table in one pass, but still define several
successive transformations. Basically, it is a LOAD statement that loads from the LOAD or SELECT
statement below, without specifying a source qualifier such as From or Resident that you would
normally do.
You can stack any number of LOAD statements this way. The statement at the bottom will be
evaluated first, then the statement above, and so on until the top statement has been evaluated. You
can achieve the same result using Resident, but in most cases a preceding LOAD will be faster.
Another advantage of preceding load is that you can keep a calculation in one place, and reuse it
in LOAD statements placed above.
Lookup:
lookup(fieldname, matchfieldname, matchfieldvalue [, tablename])
Returns the value of fieldname corresponding to the first occurrence of the value matchfieldvalue in the field matchfieldname.
Fieldname, matchfieldname and tablename must be given as strings (e.g. quoted literals).
The search order is load order unless the table is the result of complex operations such as joins, in which case the order is not well defined.
Both fieldname and matchfieldname must be fields in the same table, specified by tablename. If tablename is omitted the current table is assumed.
If no match is found, null is returned.
Hope it will help!!
