How can I set a column to be an \"\" (the empty string, equivalent to NULL in Oracle), when that column is part of a multiple-column primary key? This is the motivation...
For an application similar to URL shortener services, I want to create non guessable id\'s, which you\'re all familiar with I presume. Here\'s an example of such an id:
I will use a field named ID; an integer primary key. Is it any point to also specify a second unique field, to be able to reconstruct the tables if some ID f开发者_如何学运维ields/relationships are me
Database type: mysql Columns: Date,time,price1,qty1,price2,qty2 time will be in milliseconds number of records approx 5.5 million for a month.
I\'m looking for some guidance as to how to set up a database I am creating.I think the best way to ask the question is to describe the specific scenario:
This question already has answers here: INT vs Unique-Identifier for ID field in database 开发者_如何学运维(6 answers)
What is the limit of the length of primary key column? I\'m going to use varchar as primary key. I\'ve found no info, how long it can be, since PostgreSQL does not require to specify varchar limit whe
i write this alghorithm a and it\'s correct: Tables were : create table PrimKeyTest (primarykeycolumn varchar(8), nextcolumn int)
i 开发者_Python百科have table. which has 5 columns in that 3 of the columns makes primary key combinations.
I have a table with a Description field.I want to ensure that no two rows have the same \"Description,\" but I can\'t make Description into my identity column (my ID column is an int).
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