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Tag: unique

Generating never used before random number in SQL

I am using the function below to generate a random number between 0 and 99999999999. However, I need to make sure that the returned number has never been used before in the same app. In .net I would create a while loop and keep looping until the returned value is not found in a table that stores previously used values.

non UNIQUE constraints

So, I got in this situation: I create a table (let say model_a), in this table I have 2 cols (let say col1 and col2). I need a constraint that satisfy this reality: It’s not UNIQUE constraint, you can duplicate the first row. The only one time this constraint active is col1 is the same but col2 is different. Need


I have a table for storing coupons/discounts, and I want to use the coupon_code column as the primary key, which is a VARCHAR. My rationale is that, each coupon will have a unique code, and the only commands I will be running are SELECT … FROM … WHERE coupon_code=’..’ I won’t be doing any joins or indexing, and I don’t

Get number of values that only appear once in a column

Firstly, if it is relevant, I’m using MySQL, though I assume a solution would work across DB products. My problem is thus: I have a simple table with a single column. There are no constraints on the column. Within this column there is some simple data, e.g. I need to get the number/count of values that only appear once. From