Postgres-pgloader-列中的转换

Question

将平面文件加载到postgres表中。读取文件并加载时，我需要做一些转换。

Like
-->Check for characters, if it is present, default some value. Reg_Exp can be used in oracle. How the functions can be called in below syntax?
-->TO_DATE function from text format
-->Check for Null and defaulting some value
-->Trim functions
-->Only few columns from source file should be loaded
-->Defaulting values, say for instance, source file has only 3 columns. But we need to load 4 columns. One column should be defaulted with some value

LOAD CSV
    FROM 'filename'
    INTO postgresql://role@host:port/database_name?tablename
        TARGET COLUMNS  
            (  
                alphanm,alphnumnn,nmrc,dte
            ) 

    WITH truncate,  
         skip header = 0,  
         fields optionally enclosed by '"',  
         fields escaped by double-quote,  
         fields terminated by '|',
         batch rows = 100,
         batch size = 1MB,     
         batch concurrency = 64

    SET work_mem to '32 MB', maintenance_work_mem to '64 MB';

请帮助我，这是如何实现使用pgloader？

谢谢