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Why use multiple columns as primary keys (composite primary key)
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Another example of compound primary keys are the usage of Association tables. Suppose you have a person table that contains a set of people and a group table that contains a set of groups. Now you want to create a many to many relationship on person and group. Meaning each person can belong t...
SQL Server Output Clause into a scalar variable
Is there any "simple" way to do this or I need to pass by a table variable with the "OUTPUT ... INTO" syntax?
3 Answers
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An explicit value for the identity column in table can only be specified when a column list is used
...e identity column in tbl_A_archive a regular, non-identity column: If your table is an archive table and you always specify an explicit value for the identity column, why do you even need an identity column? Just use a regular int instead.
Details on Solution 1
Instead of
SET IDENTITY_INSERT archi...
Client-server synchronization pattern / algorithm?
...g every change (insert, update or delete) from any device into a "history" table. So if, for example, someone changes their phone number in the "contact" table, the system will edit the contact.phone field, and also add a history record with action=update, table=contact, field=phone, record=[contact...
Failed to enable constraints. One or more rows contain values violating non-null, unique, or foreign
...is raised:
Then within the command window, call GetErrors method on the table getting the error.
For C#, the command would be ? dataTable.GetErrors()
For VB, the command is ? dataTable.GetErrors
This will show you all datarows which have an error. You can get then look at the RowError for each...
Is there a typical state machine implementation pattern?
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I prefer to use a table driven approach for most state machines:
typedef enum { STATE_INITIAL, STATE_FOO, STATE_BAR, NUM_STATES } state_t;
typedef struct instance_data instance_data_t;
typedef state_t state_func_t( instance_data_t *data );
s...
What is a stored procedure?
...ut the user will not need to have read/write permissions on the underlying tables. This is a good first step against SQL injection.
Stored procedures do come with downsides, basically the maintenance associated with your basic CRUD operation. Let's say for each table you have an Insert, Update, Del...
Cannot insert explicit value for identity column in table 'table' when IDENTITY_INSERT is set to OFF
...tionId that is an identity column.
You can turn on identity insert on the table like this so that you can specify your own identity values.
SET IDENTITY_INSERT Table1 ON
INSERT INTO Table1
/*Note the column list is REQUIRED here, not optional*/
(OperationID,
OpDescription...
How to efficiently build a tree from a flat structure?
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Store IDs of the objects in a hash table mapping to the specific object. Enumerate through all the objects and find their parent if it exists and update its parent pointer accordingly.
class MyObject
{ // The actual object
public int ParentID { get; set; ...
Primary key or Unique index?
...e two equal values in that column in two different rows. Example:
CREATE TABLE table1 (foo int, bar int);
CREATE UNIQUE INDEX ux_table1_foo ON table1(foo); -- Create unique index on foo.
INSERT INTO table1 (foo, bar) VALUES (1, 2); -- OK
INSERT INTO table1 (foo, bar) VALUES (2, 2); -- OK
INSERT ...