- What are the constraints in SQL?
- Is primary key a constraint?
- How do I change primary key?
- How can remove primary key constraint in SQL Server?
- How do I change unique constraints in SQL Server?
- How do I find constraints in SQL Server?
- How do I find unique constraints in SQL Server?
- What are the types of constraints?
- What is difference between unique and primary key constraints?
- Can foreign key be null?
- How can change primary key constraint in SQL Server?
- What is difference between index and primary key?
- Is default a constraint in SQL?
- Which statement is wrong about primary key constraint in SQL?
What are the constraints in SQL?
SQL Constraints are rules used to limit the type of data that can go into a table, to maintain the accuracy and integrity of the data inside table.
Constraints can be divided into the following two types, Column level constraints: Limits only column data..
Is primary key a constraint?
The PRIMARY KEY constraint uniquely identifies each record in a table. Primary keys must contain UNIQUE values, and cannot contain NULL values. A table can have only ONE primary key; and in the table, this primary key can consist of single or multiple columns (fields).
How do I change primary key?
Set the primary key using fields you already have in AccessOpen the database that you want to modify.In the Navigation Pane, right click the table in which you want to set the primary key and, on the shortcut menu, click Design View. … Select the field or fields that you want to use as the primary key.More items…
How can remove primary key constraint in SQL Server?
The syntax to drop a primary key in SQL is: ALTER TABLE table_name DROP PRIMARY KEY; table_name.
How do I change unique constraints in SQL Server?
To modify a unique constraintIn the Object Explorer, right-click the table containing the unique constraint and select Design.On the Table Designer menu, click Indexes/Keys….In the Indexes/Keys dialog box, under Selected Primary/Unique Key or Index, select the constraint you wish to edit.More items…•
How do I find constraints in SQL Server?
To view the source code using SQL Server Management Studio get into the “Object Explorer”. From there you expand the “Master” database, then expand “Programmability”, then “Stored Procedures”, then “System Stored Procedures”. You can then find “sys. sp_helpconstraint” and right click it and select “modify”.
How do I find unique constraints in SQL Server?
Use sys. indexes, join the table, schema, object, and as an added bonus, you get not only unique constraints, but also unique indices, including filter. Here is a better solution, which lists the constraint columns in a proper sort order, with added ASC/DESC flag.
What are the types of constraints?
An informational constraint is an attribute of a certain type of constraint, but one that is not enforced by the database manager.NOT NULL constraints.Unique constraints.Primary key constraints.(Table) Check constraints.Foreign key (referential) constraints.Informational constraints.
What is difference between unique and primary key constraints?
The difference between a UNIQUE constraint and a Primary Key is that per table you may only have one Primary Key but you may define more than one UNIQUE constraints. Primary Key constraints are not nullable. UNIQUE constraints may be nullable. … A UNIQUE constraint will generate a unique NON-CLUSTERED INDEX.
Can foreign key be null?
A foreign key containing null values cannot match the values of a parent key, since a parent key by definition can have no null values. However, a null foreign key value is always valid, regardless of the value of any of its non-null parts. … A table can have many foreign keys.
How can change primary key constraint in SQL Server?
To modify a primary key, execute an ALTER TABLE… DROP PRIMARY KEY statement to drop the existing primary key, and then execute an ALTER TABLE… ALTER column-name column-alteration statement to set the new primary key for the table.
What is difference between index and primary key?
PRIMARY KEY indexes From an indexing perspective, defining a column or columns as a PRIMARY KEY is very similar to creating a UNIQUE index. The main difference is that PRIMARY KEYs cannot hold null values. However, like UNIQUE indexes, PRIMARY KEYs cannot hold duplicates.
Is default a constraint in SQL?
The DEFAULT constraint is used to insert a default value into a column. The default value will be added to all new records, if no other value is specified.
Which statement is wrong about primary key constraint in SQL?
Q. 1. Which statement is wrong about PRIMARY KEY constraint in SQL? Primary keys must contain UNIQUE values.