SQL UNIQUE constraints ensure data uniqueness in databases, critical for identifiers like emails or SSNs. SELECT DISTINCT queries retrieve unique values, while COUNT DISTINCT counts unique entries, aiding in data analysis and maintaining data integrity. These SQL features are vital for database management.
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SQL UNIQUE constraints ensure the uniqueness of data in a database table
Adding UNIQUE constraints during table creation
UNIQUE constraints can be specified at the time of table creation using the CREATE TABLE statement
Adding UNIQUE constraints to an existing table
UNIQUE constraints can be added to an existing table using the ALTER TABLE statement
The database management system automatically checks for duplicates when inserting or updating data
SELECT DISTINCT is used to retrieve unique values from a table
Generating reports with unique entries
SELECT DISTINCT is useful for creating reports that require unique data
Cleaning up data
SELECT DISTINCT can be used to remove duplicate entries from a dataset
Preparing data for visualization
SELECT DISTINCT is helpful in preparing data for visualization tools
COUNT DISTINCT is used to count the number of unique entries in a column
Tracking user engagement
COUNT DISTINCT can be used to track the number of unique users engaging with a platform
Identifying data irregularities
COUNT DISTINCT is helpful in identifying any irregularities in data
Assessing marketing campaign effectiveness
COUNT DISTINCT can be used to measure the impact of marketing campaigns by counting unique customers
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To maintain data integrity, ______ or ______ can be used to add UNIQUE constraints to new or existing tables respectively.
CREATE TABLE
ALTER TABLE
01
UNIQUE constraint purpose
Prevents duplicate values in a column to maintain data integrity.
02
UNIQUE constraint check timing
Checked during record insertion and update operations.
