Add Constraint

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ALTER TABLE Employees
ADD CONSTRAINT DefaultSalary DEFAULT ((100)) FOR [Salary]

This adds a constraint called DefaultSalary which specifies a default of 100 for the Salary column.

A constraint can be added at the table level.

Types of constraints

Primary Key - prevents a duplicate record in the table
Foreign Key - points to a primary key from another table
Not Null - prevents null values from being entered into a column
Unique - uniquely identifies each record in the table
Default - specifies a default value
Check - limits the ranges of values that can be placed in a column

To learn more about constraints, see the Oracle documentation.

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ALTER TABLE:

* ALTER TABLE

* Add Columns

* Drop Column

* Add Primary Key

* Drop Constraint

* Alter Column

* Add Constraint

Table Of Contents

0 Getting started with SQL

1 SELECT

2 JOIN

3 Example Databases and Tables

4 UPDATE

5 Indexes

6 CREATE TABLE

7 UNION, UNION ALL

8 ALTER TABLE

9 CASE

10 INSERT

11 Primary Keys

12 ORDER BY

13 GROUP BY

14 Filter results using WHERE and HAVING

15 Window Fnctions

16 Common Table Expressions

17 Views

18 LIKE operator

19 Functions Aggregate

20 DELETE

21 String Functions

22 Data Types

23 AND OR operators

24 Triggers

25 TRUNCATE

26 MERGE

27 Foreign Keys

28 Finding Duplicates on a Column Subset with Detail

29 Sequence

30 Comments

31 Subqueries

32 Execution blocks

33 Stored Procedures

34 DROP Table

35 Row number

36 Transactions

37 CREATE FUNCTION

38 SQL Group by vs. Distinct

39 Table Design

40 CROSS APPLY and OUTER APPLY

41 Synonyms

42 CREATE database

43 SKIP TAKE pagination

44 EXPLAIN and DESCRIBE

45 Information Schema

46 IN clause

47 NULL

48 SQL Injection

49 Cascading Delete

50 Order of Execution

51 DROP or DELETE database

52 EXCEPT

53 TRYCATCH

54 XML

55 GRANT and REVOKE

56 Functions ScalarSingle Row

57 Relational Algebra

58 EXISTS CLAUSE

59 Materialized Views

60 Functions Analytic

61 SQL CURSOR

62 Identifier

63 Clean Code in SQL

64 Contributors