为什么要创建自定义异常？(Why Create Custom Exceptions? [closed])

 在回答您的问题之前，请先评论您的SQL函数。 
 
 它不会失败，因为语句以错误的顺序执行，但是因为在执行第一个查询之前解析了两个查询。 你得到的错误信息有点像 
 
ERROR:  relation "first_table" does not exist
[...]
CONTEXT:  SQL function "doboth" during startup
 
 请注意“启动期间”。 
 
 Aswers 
 
 
 
 您可能会遇到轻微的性能提升，特别是在SQL语句很复杂的情况下，因为PL / pgSQL函数中的SQL语句计划在数据库会话期间被缓存，或者直到它们失效。 
 如果PL / pgSQL函数缓存了查询计划，但每次都必须计划调用该函数的SQL语句，那么由于执行该函数的开销，实际上可能会更糟糕。 
 
 
 每当使用不同的模式名称调用该函数时，查询计划将失效并且必须重新创建。 因此，如果您为每次调用更改架构名称，您将无法获得任何收益。 
 
 
 SQL函数不缓存查询计划，因此它们的执行效果不如普通的SQL查询。 
 
 
 但请注意，在函数中缓存简单SQL语句的收益并不是很大。 
 
 使用仅作为SQL语句容器的函数，只有这样才能使生活更简单，否则使用纯SQL。 
 
 不仅要关注性能设计，还要关注良好的架构和简单的设计。 
 
 如果相同的语句不断重复，那么使用预处理语句可能比使用函数获得更多性能。 

Before I answer your questions, a remark to your SQL function.
 
It does not fail because the statements are executed in a wrong order, but because both queries are parsed before the first one is executed. The error message you get is somewhat like
 
ERROR:  relation "first_table" does not exist
[...]
CONTEXT:  SQL function "doboth" during startup
 
Note the “during startup”.
 
Aswers
 
 
 
You may experience a slight performance boost, particularly if the SQL statements are complicated, because the plans of SQL statements in a PL/pgSQL function are cached for the duration of a database session or until they are invalidated.
 
If the plan for the query is cached by the PL/pgSQL function, but the SQL statement calling the function has to be planned every time, you might actually be worse of from a performance angle because of the overhead of executing the function.
 
 
Whenever you call the function with a different schema name, the query plan will be invalidated and has to be created anew. So if you change the schema name for every invocation, you won't gain anything.
 
 
SQL function don't cache query plans, so they don't perform better than the plain SQL query.
 
 
Note, however, that the gains from caching simple SQL statements in functions are not tremendous. 
 
Use functions that just act as containers for SQL statements only if it makes life simpler for you, otherwise use plain SQL.
 
Do not only focus on performance uring design, but on a good architecture and a simple design.
 
If the same statements keep repeating over and over, you might gain more performance using prepared statements than using functions.