The following statement: CONSTRAINT pk_UserID PRIMARY KEY (U_Id) Is the same as this one: CONSTRAINT pk_UserID PRIMARY KEY CLUSTERED (U_Id) You can only have the table data physicality ordered by one of the indexes, and by default that index is the one used for the primary key (the primary key unique constraint is always supported … Read more
UUID returns a universal unique identifier (hopefuly also unique if imported to another DB as well). To quote from MySQL doc (emphasis mine): A UUID is designed as a number that is globally unique in space and time. Two calls to UUID() are expected to generate two different values, even if these calls are performed … Read more
Is it bad to have text as a primary key in an SQLite database? I heard that it’s bad for performance reasons, is this true? From correctness point of view, TEXT PRIMARY KEY is all right. From performance point of view, prefer INTEGER keys. But as with any performance issue, measure it yourself to see … Read more
I also faced with similar problem and found the following solution // Entity Framework Core public virtual int GetKey<T>(T entity) { var keyName = Context.Model.FindEntityType(typeof (T)).FindPrimaryKey().Properties .Select(x => x.Name).Single(); return (int)entity.GetType().GetProperty(keyName).GetValue(entity, null); }
Converting an int to a serial more or less only means adding a sequence default to the value, so to make it a serial; Pick a starting value for the serial, greater than any existing value in the table SELECT MAX(id)+1 FROM mytable Create a sequence for the serial (tablename_columnname_seq is a good name) CREATE … Read more
For MS SQL Server: SCOPE_IDENTITY() will return you the last generated identity value within your current scope: SELECT SCOPE_IDENTITY() AS NewID
There can only be one primary key per table – as indicated by the word “primary”. You can have additional UNIQUE columns like: CREATE TABLE test( sl_no int PRIMARY KEY, — NOT NULL due to PK emp_id int UNIQUE NOT NULL, emp_name text, emp_addr text ); Columns that are (part of) the PRIMARY KEY are … Read more
Yes. The only way would be to drop the constraint with an Alter table then recreate it. ALTER TABLE <Table_Name> DROP CONSTRAINT <constraint_name> ALTER TABLE <Table_Name> ADD CONSTRAINT <constraint_name> PRIMARY KEY (<Column1>,<Column2>)
Technically yes, but if a string makes sense to be the primary key then you should probably use it. This all depends on the size of the table you’re making it for and the length of the string that is going to be the primary key (longer strings == harder to compare). I wouldn’t necessarily … Read more
In Oracle, you could do this: create table D ( ID numeric(1), CODE varchar(2), constraint PK_D primary key (ID, CODE) );