Найдите дубликаты колонки MySQL
SELECT name, COUNT(*) c FROM table GROUP BY name HAVING c > 1;
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SELECT name, COUNT(*) c FROM table GROUP BY name HAVING c > 1;SELECT varchar_col
FROM table
GROUP BY varchar_col
HAVING COUNT(*) > 1;
SELECT
t1.primary_id,
t1.duplicate_id,
t1.data1,
t1.data2
FROM
table_name t1
LEFT JOIN table_name t2
ON (t1.duplicate_id = t2.duplicate_id AND t1.primary_id < t2.primary_id)
WHERE
t2.primary_id IS NULL
## Find ALL duplicate recods by value (without grouping them by value) ##
# to find the duplicate,
# replace all instances of tableName with your table name
# and all instances of duplicateField with the field name where you look for duplicates
SELECT t1.*
FROM tableName AS t1
INNER JOIN(
SELECT duplicateField
FROM tableName
GROUP BY duplicateField
HAVING COUNT(duplicateField) > 1
)temp ON t1.duplicateField = temp.duplicateField
order by duplicateField