单条和批处理的问题体现。。。至今想不通。。。

方式一单条：
UPDATE new_loan_balance a
SET a.prdt_biz_ctgy = CASE
WHEN a.prdt_biz_ctgy = "01" THEN "对公贷款"
WHEN a.prdt_biz_ctgy = "02" THEN "对私贷款"
WHEN a.prdt_biz_ctgy = "41" THEN "贸易融资"
ELSE NULL
END;

方式二批处理：
update new_loan_balance a set a.prdt_biz_ctgy = ‘对公贷款‘ where a.prdt_biz_ctgy = ‘01‘;
update new_loan_balance a set a.prdt_biz_ctgy = ‘对私贷款‘ where a.prdt_biz_ctgy = ‘02‘;
update new_loan_balance a set a.prdt_biz_ctgy = ‘贸易融资‘ where a.prdt_biz_ctgy = ‘41‘;

为什么方式一非常慢（几小时）， 方式二很快（几毫秒）

原文：https://blog.51cto.com/daxionglaiba/2408703