MySQL: understanding sql code

Question

I'm trying to understand some code created by someone who is not anymore working in this project, but I'm having some difficulties to understand the following line. I thought some one more experienced using mysql would be able to help me with this.

here it goes the line code:

SET price_calc=(REPLACE(@price,',','.') * IF(SUBSTRING(nmu,-1)='I', 1.414819,1.21))";

This SET is part of the LOAF DATA INFILE statement, and the part I don't understand is this expression:

LOAD DATA [LOW_PRIORITY | CONCURRENT] [LOCAL] INFILE 'file_name'
[REPLACE | IGNORE]
INTO TABLE tbl_name
[CHARACTER SET charset_name]
[{FIELDS | COLUMNS}
    [TERMINATED BY 'string']
    [[OPTIONALLY] ENCLOSED BY 'char']
    [ESCAPED BY 'char']
]
[LINES
    [STARTING BY 'string']
    [TERMINATED BY 'string']
]
[IGNORE number LINES]
[(col_name_or_user_var,...)]
[SET col_name = expr,...] -- this corresponds to the line that uses the expression I'm not understanding

Can you help me understanding what it is saying?

Answer 1

SET price_calc=(REPLACE(@price,',','.') * IF(SUBSTRING(nmu,-1)='I', 1.414819,1.21))";

The SET price_calc is going to set the value for a column named "price_calc". It will set it to the result of the calculation on the right-hand side of the "=".

This

(REPLACE(@price,',','.') * IF(SUBSTRING(nmu,-1)='I', 1.414819,1.21))

simplifies to

first-expression * second-expression

The first expression is

REPLACE(@price,',','.')

It replaces commas with periods in @price . Some locales use a comma as a decimal point; your database apparently does not.

The second expression is

IF(SUBSTRING(nmu,-1)='I', 1.414819,1.21)

That means you multiply first-expression by either 1.414819 or 1.21, depending on the value of SUBSTRING(nmu,-1) .