I use a Luhn algorithm to generete random number, inserted below sql code to column 'SKU"

ALTER TABLE m_product ALTER sku SET DEFAULT ltrim(to_char(luhn_generate(round(random()*10000)::int), '00000'))

as a result on record saving random number is generated, but my problem is the numbers are not unique.

Somone sugest that I should write a function to encapsulate "ltrim(to_char(luhn_generate(

round(random()*10000)::int), '00000'))" and at the same time, check if the value is already used in the table.

in pseudo code it would look something like this:

generateMProductSKU(){
    skuGen=""
    needToGenerate = true
    while(needToGenerate){
      skuGen = ltrim(to_char(luhn_generate(round(random()*10000)::int), '00000'))
      if((Select count(*) from M_Product where sku =skuGen) = 0
         needToGenerate = false
   }
   return skuGen
}

Culd somebody help me tu structure code into right sql format so it could be inserted into database.

Thank you very much.

Peter