sqlite unique constraint code example

Example 1: sqlite make primary key

# SQLite ->
//if the primary key has only one column,
//you use the PRIMARY KEY column constraint 
//to define the primary key as follows: 
  
  CREATE TABLE table_name(
   column_1 INTEGER NOT NULL PRIMARY KEY,
   ...
);

// in case primary key consists of two or 
//more columns, you use the PRIMARY KEY table 
//constraint to define the primary as shown in 
//the following statement.

  CREATE TABLE table_name(
     column_1 INTEGER NOT NULL,
     column_2 INTEGER NOT NULL,
     ...
     PRIMARY KEY(column_1,column_2,...)
  );

Example 2: how to drop a unique constraint in sql

SHOW CREATE TABLE [tableName]
-- Find the constraintID after CONSTRAINT 'constraintID'
ALTER TABLE [tableName] DROP FOREIGN KEY constraintID

Example 3: sqlite unique

sqlite uniue
-------------------------        
CREATE TABLE contacts(
  contact_id INTEGER PRIMARY KEY,
  first_name TEXT,
  last_name TEXT,
  email TEXT NOT NULL UNIQUE
);