Use of Oracle Constraints

--5 constraints, PRIMARY KEY constraints, FOREIGN KEY constraints, UNIQUE constraints, check constraints, non-null constraints.

--Add PRIMARY KEY constraint Alter table table_name add constraints Constraint_name Primary key (column_name);

--Syntax description constraint_name: Constraint name. COLUMN_NAME: PRIMARY KEY constraint specifies the column name in the data table.

--Remove the PRIMARY KEY constraint Alter table table_name Drop constraint constraint_name;

--FOREIGN KEY constraint

--Add a FOREIGN key constraint directly in the table, and you need to add the following statement to the last side as you create it

Constraint constraint_name foreign key (COLUMN_NAME) reference table_name (column_name) on DELETE cascade;

--Syntax Description constraint_name: The name of the foreign KEY constraint.

Foreign KEY (column_name): Specifies the column name of the foreign KEY constraint.

Reference: The table name (column name) that needs to be referenced.

On DELETE CASCADE: Set cascade Delete, when the primary key bullet is deleted, the field corresponding to the foreign key is also deleted.

--Add a FOREIGN key constraint directly after creating the table

Alter table table_name Add constraint constraint_name foreign key (COLUMN_NAME) reference table_name (COLUMN_NAME) on Delet e Cascade;

--delete foreign KEY constraint

Alter table table_name drop constraint constraint_name;

--check constraints

--When creating a table, add a check constraint and add a constraint directly behind the field

Constraint constraint_name Check (condition);

Condition: is the condition for checking constraints.

--alter Table Add Check Constraint

Alter table table_name ADD constraint constraint_name check (condition);

--delete Check constraint Alter

Table table_name Drop constraint constraint_name;

--unique constraints, UNIQUE constraints,

CREATE TABLE adds UNIQUE constraint constraint constraint_name unique (column_name);

--Add a unique constraint when modifying a table

Alter table table_name ADD constraint constraint_name unique (column_name);

--The only constraint to remove a table

Alter table table_name Drop constraint constraint_name;

--Create non-null constraints, add non-null constraints directly when creating tables

... not NULL,

--Add a non-null constraint when modifying a table

Alter Table table_name Modify column_name NOT NULL;

--truncate completely deletes the table and cannot be recovered after deletion.

TRUNCATE TABLE table_name;

--merge statements, batch modification and bulk increment statements

Merge [into] table_name1 using table_name2 on (condition) while matched then merge_update_clause when not matched then Mer    Ge_insert_clause; --Syntax Description table_name1: The table to be modified or added.

Table_name2: Reference to the Update table.  The relationship between CONDITION:TABLE_NAME1 and TABLE_NAME, or some other condition. Merge_update_clause: The update operation is performed if the conditions in the reference table table_name2 are matched. (Update set Column_name1=column_name2) Merge_insert_clause: Performs a new operation if the condition does not match. (INSERT INTO (column_name2,column_name2,...))

Use of Oracle Constraints