捕获异常

PostgreSQL 中的事务与错误处理

Jason Myers

Principal Engineer

出错的语句

INSERT INTO sales (name, quantity, cost) 
VALUES 
  ('chocolate chip', 6, null);

ERROR:  null value in column "cost" violates not-null constraint
DETAIL:  Failing row contains 
(1, "chocolate chip", 6, null, 2020-04-28 19:58:55.715886).

通用异常捕获

tryCatch(
  sqrt("a"), 
  error=function(e) 
    print("Boom!")
)

Python

try:
   math.sqrt("a")
except Exception as e:
   print("Boom!")

PL/pgSQL

BEGIN 
SELECT 
  SQRT("a");
EXCEPTION WHEN others THEN RAISE INFO 'Boom!';
END;

结果

     R: Boom!
Python: Boom!
   SQL: INFO: Boom!

PL/pgSQL DO 命令（匿名函数）

DO $$

DECLARE
   some_variable text;

BEGIN
    SELECT text from a table;
END;

$$ language 'plpgsql';

异常处理函数

DO $$
BEGIN
    SELECT SQRT("a");
EXCEPTION
    WHEN others THEN
       INSERT INTO errors (msg) VALUES ('不能对字符串求平方根。');
       RAISE INFO '不能对字符串求平方根。';
END; 
$$ language 'plpgsql';

合理使用异常处理

使用 EXCEPTION 子句会带来明显开销
用 Python 或 R 处理异常更高效

解决异常时不要牺牲正确的上下文
在理解异常前不要过早优化

¹ https://www.postgresql.org/docs/12/plpgsql-control-structures.html {{1}}

切换数据集

patients

column	type
patient_id	integer
a1c	double (float)
glucose	integer
fasting	boolean
created_on	timestamp

errors

column	type
error_id	integer
state	string
msg	string
detail	string
context	string

¡Vamos a practicar!

PostgreSQL 中的事务与错误处理