Mass updating magento product weights from a csv

Assume you've created a local table from your csv with two columns: sku, weight.

SELECT cped.value, cpe.sku, update.\*
FROM catalog_product_entity_decimal cped
INNER JOIN eav_attribute ea ON ea.attribute_id = cped.attribute_id AND ea.attribute_code = 'weight'
INNER JOIN catalog_product_entity cpe ON cpe.entity_id = cped.entity_id
INNER JOIN \_product_weight_updates update ON update.sku = cpe.sku
LIMIT 20

UPDATE catalog_product_entity_decimal cped
INNER JOIN eav_attribute ea ON ea.attribute_id = cped.attribute_id AND ea.attribute_code = 'weight'
INNER JOIN catalog_product_entity cpe ON cpe.entity_id = cped.entity_id
INNER JOIN \_product_weight_updates update ON update.sku = cpe.sku
SET cped.value = update.weight
WHERE cpe.sku = update.sku
SELECT cped.value, cpe.sku, update.\*
FROM catalog_product_entity_decimal cped
INNER JOIN eav_attribute ea ON ea.attribute_id = cped.attribute_id AND ea.attribute_code = 'weight'
INNER JOIN catalog_product_entity cpe ON cpe.entity_id = cped.entity_id
INNER JOIN \_product_weight_updates update ON update.sku = cpe.sku
LIMIT 20

UPDATE catalog_product_entity_decimal cped
INNER JOIN eav_attribute ea ON ea.attribute_id = cped.attribute_id AND ea.attribute_code = 'weight'
INNER JOIN catalog_product_entity cpe ON cpe.entity_id = cped.entity_id
INNER JOIN \_product_weight_updates update ON update.sku = cpe.sku
SET cped.value = update.weight
WHERE cpe.sku = update.sku