sql don't allow duplicates code example

Example 1: t-sql get duplicate rows

SELECT [CaseNumber], COUNT(*) AS Occurrences
FROM [CaseCountry]
GROUP BY [CaseNumber]
HAVING (COUNT(*) > 1)

Example 2: sql delete duplicate rows but keep one

# Step 1: Copy distinct values to temporary table
CREATE TEMPORARY TABLE tmp_user (
    SELECT id, name 
    FROM user
    GROUP BY name
);

# Step 2: Remove all rows from original table
DELETE FROM user;

# Step 3: Remove all rows from original table
INSERT INTO user (SELECT * FROM tmp_user);

# Step 4: Remove temporary table
DROP TABLE tmp_user;