Answers to Interview Questions #2

1. What is the difference between a Mapping parameter and a Session Parameter?

Mapping parameters use the following naming convention: $$VARIABLE_NAME, while Session parameters use only one dollar sign ($).

Mapping parameters can have any name ($$Manny_Pacquiao) while Session parameters follow strict naming conventions ($OutputFile_NAME for output files – this will not work for reject files).

Mapping parameters are used within mappings. Session parameters define session settings.

Both mapping and session parameters can be defined within a single parameter file.

2. What is the difference between a Mapping Parameter and a Mapping Variable?

Mapping Parameters are defined via the parameter file and cannot change values within the mapping.

Mapping Variables are defined and can be changed within the mapping.

3. Given a file with 1000 rows, how will you display the 500th row in Unix?

Use the following syntax: head –500 filename | tail –1

4. What is the difference between Unix commands grep and find?

find is used to search keywords in files within a directory.

grep is used to find keywords within contents of a file/files.

5. How does the Unix command wc work?

wc stands for word count. In short, it counts the number of words in a file.

A useful switch for this command is –l. wc –l counts the number of lines/records in a file.

6. How would you show duplicates in a table using SQL?

Use the following syntax:

select key_column, count(*) from table_name
group by key_column
having count(*)>1

7. More Informatica Performance solutions.

Use a sorter before a lookup for very large lookup tables. The sort order in the sorter should match the sort order in the lookup.

This reduces memory-swapping by ensuring that all fields in the cache are used up first before the swap.