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How to get the primary key of a table?
{TABLENAME} = your table name from which you want to see the primary key. NOTE : enter your database name and table name without brackets. The code I’ll give you works and retrieves not only keys, but a lot of data from a table in SQL Server. Is tested in SQL Server 2k5/2k8, dunno about 2k. Enjoy!
Can a primary key be used as a clustered key?
It’s not recommended to use the primary key as a clustered key without checking whether that is the optimal solution in you scenario first. Also, note the difference between a primary key and clustered index – a primary key can’t have duplicate or null values, while a clustered index can.
How does indexing affect the performance of a query?
But even the indexes that provide better performance for some operations, can add overhead for others. While executing a SELECT statement is faster on a clustered table, INSERTs, UPDATEs, and DELETEs require more time, as not only data is updated, but the indexes are updated also.
Can a table have more than one candidate key?
A table can have multiple candidate keys. Each candidate key is a column or set of columns that are UNIQUE, taken together, and also NOT . Thus, specifying values for all the columns of any candidate key is enough to determine that there is one row that meets the criteria, or no rows at all.
How to count the number of instances of each foreign-key?
In other words, return every column for ALL rows in the Books table, along with a calculated column named ‘number_of_orders’ that counts the number of times each book appears in the Orders table. (If a book does not occur in the orders table, the book should be listed in the result set, but “number_of_orders” should be zero.
How to have multiple pK’s in one table?
Then choose one of the two keys as the PK and put a unique index on the other (the autogenerated field does not have to be a PK). And make sure to add the FK to the field that is in the parent table.