Typically, you apply the unique constraints to columns when you create the table using the inline constraint syntax as follows: ALTER TABLE table-name DROP UNIQUE constraint-name Dropping this unique constraint invalidates any packages or cached … Thanks for the question, Tomas.
SQL UNIQUE KEY constraint on CREATE TABLE: Important points about UNIQUE CONSTRAINT in Oracle SQL / PLSQL: In Oracle SQL / PLSQL a UNIQUE CONSTRAINT can be created by using maximum of 32 columns / fields. CodeProject, 503-250 Ferrand Drive Toronto Ontario, M3C 3G8 Canada +1 416-849-8900 x 100
A PRIMARY KEY constraint automatically has a UNIQUE constraint defined on it. A unique constraint is a single field … A UNIQUE CONSTRAINT can be dropped, disabled and enabled in ALTER TABLE statement. The unique key and primary key both provide a guarantee for uniqueness for a column or a set of columns. If you need to make a change to a table's constraints (for example to drop an existing single column constraint in order to create a new compound column constraint) then use the following SQL:
UNIQUE constraint vs. PRIMARY KEY constraint. As we know that SHOW INDEX statement is used for this purpose. This SQL Server tutorial explains how to create, add, and drop unique constraints in SQL Server with syntax and examples. If you created the index explicitly with the CREATE INDEX statement, then you can drop the index with the DROP INDEX statement. is alter table drop constraint drop index syntactically valid? The DROP UNIQUE clause of the ALTER TABLE statement drops the definition of the unique constraint constraint-name and all referential constraints that are dependent upon this unique constraint. It is the same command for unique property, property existence and node key constraints. How to you drop a unique row constraint in PostgreSQL? Breadcrumb. Oracle unique constraint syntax A unique constraint is an integrity constraint that ensures the data stored in a column, or a group of columns, is unique among the rows in a table. There may be many unique key constraints for one table, but only one PRIMARY KEY constraint for one table. The following statement drops the emp_ename index: Although both UNIQUE and PRIMARY KEY constraints enforce the uniqueness of data, you should use the UNIQUE constraint instead of PRIMARY KEY constraint when you want to enforce the uniqueness of a column, or a group of columns, that are not the primary key columns. The constraint-name must identify an existing unique constraint. The ‘key_name’ in the result set of SHOW INDEX statement Question and Answer. However, in contrast to the unique index, you cannot specify the IGNORE_DUP_KEY, DROP_EXISTING, PAD_INDEX , and STATISTICS_NORECOMPUTE options for the unique constraint in the ALTER TABLE statements.