encontrar filas duplicadas en mysql con ejemplo de código de múltiples columnas

Ejemplo 1: buscar columnas mysql duplicadas

SELECT name, COUNT(*) c FROM table GROUP BY name HAVING c > 1;

Ejemplo 2: encontrar claves duplicadas en mysql

SELECT col, COUNT(col) FROM table_name GROUP BY col HAVING COUNT(col) > 1;

Ejemplo 3: mysql encuentra duplicados en la misma tabla

## 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

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